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    Ben Schuler

    Gilad Haran


    Hagen Hofmann

    Next Speaker: Thomas Perkins (August 15)

    Jane Clarke.jpg

    Jane Clarke

    Department of Chemistry, University of Cambridge

    Making Sense of Disorder 

    Monday 04.05.

    7:00 PDT - 10:00 EDT - 14:00 UTC

    15:00 UK - 16:00 CET - 17:00 IL

    Zoom:      Inactive



    Monday 18.05.

    8:00 PDT - 11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Astbury Centre for Structural and Molecular Biology, University of Leeds

    Early Steps in Amyloid Assembly:

    The Achilles Heel of a Disease Mechanism 

    Many amyloid precursors are intrinsically disordered, while others are folded, yet both can assemble into the highly organised cross-bstructures characteristic of amyloid. Understanding how this conformational transition occurs is not clear, with the initiating steps in aggregation being particularly difficult to study because of the dynamics and heterogeneity of the species involved. Focussing on the IDP α-synuclein (αSyn), linked to pathology in Parkinson’s disease, and b2-microglobulin involved in Dialysis Amyloidosis, I will discuss our understanding of the early steps in amyloid formation and describe how we are beginning to target these steps specifically to prevent amyloid formation. 

    Zoom:       Inactive


    Sheena Radford


    Monday 01.06.

    8:00 PDT - 11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Ken A. Dill

    Laufer Center for Physical and Quantitative Biology, Stony Brooks University

    How the forces on proteomes manifest as cell behaviors 

    Cells adapt to their environments.  Adaptive forces in homeostasis or evolution are expressed in terms of growth laws and fitness landscapes.  Some aspects of fitness arise from specific actions of individual proteins.  But other aspects arise from more physical, less specific, more universal actions of all proteins in the proteome.  We are modeling how protein folding, aggregation, diffusion, and chaperoning contribute to cellular adaptations.

    Lewis Kay.jpg

    Monday 15.06.

    8:00 PDT - 11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Lewis E. Kay

    Department of Molecular Genetics, Biochemistry and Chemistry, University of Toronto

    The important role of dynamics in the function and misfunction of molecular machines

    Protein molecules play critical roles in cellular function and they catalyze many of the biochemical reactions that are necessary for life. The three-dimensional shapes of these molecules are crucial for guiding proper function and they can change with time due to interactions with other molecules, various stresses on the cell or simply the result of random fluctuations. Although very detailed static pictures of protein molecules have been produced using traditional biophysical tools, macromolecular function and misfunction is, in many cases, intimately coupled to flexibility and knowledge of molecular motions therefore becomes critical. For the past 3 decades my laboratory has developed biophysical techniques, focusing on solution based Nuclear Magnetic Resonance spectroscopy for the study of biomolecular dynamics. A brief description of some of the methods we have derived will be given along with examples to illustrate the critical importance of dynamics to protein function and misfunction.


    Martin Gruebele

    Department of Chemistry, University of Illinois at Urbana-Champaign

    Protein folding and association dynamics: from in silico to in vitro to in vivo

    Protein folding and binding reactions are generally quite fast and involve small free energy differences. As a result, they can be sensitive to the environment that biases protein energy landscapes. I will discuss molecular dynamics simulations, test-tube experiments, in-cell measurements, and measurements in living animals that highlight the sensitivity of protein dynamics to its solvation environment.

    Monday 29.06.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL


    Monday 13.07.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Jane Dyson

    Department of Integrative Structural and Computational Biology, The Scripps Research Institute

    NMR Dynamics Studies of Protein Folding Intermediates

    Jane Dyson and Peter Wright

    The transient intermediate states that are populated as a protein folds are difficult to access and study. Both kinetic and equilibrium biophysical methods have been used to probe these states, using chemically or physically unfolded and partly folded states as models. NMR gives unique information on the local motions of a protein chain. The ps-ns time scale motions of the polypeptide backbone in unfolded and partly folded states, measured using relaxation rates, can give important insights into the factors that contribute to progress along the folding pathway. In addition, we can study states at low populations within a conformational ensemble using relaxation dispersion measurements that probe ms-ms motions, which are of particular interest in the folding processes of proteins.


    Dave Thirumalai

    Department of Chemistry, The University of Texas at Austin

    Iterative Annealing Mechanism for GroEL

    Most cytosolic proteins fold spontaneously as envisioned by Anfinsen. However, there are number of proteins that require the chaperone machinery to reach their functionally competent states. Using theory, simple arguments, and simulations using coarse-grained models I will describe the workings of the E. Coli. chaperonin GroEL.  A framework based on the Iterative Annealing Mechanism that unifies inefficient folding under non-permissive conditions, GroEL allostery, and function will be presented.  If time permits some open problems will be discussed.

    Monday 27.07.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL


    Peter G. Wolynes

    Department of Chemistry, Rice University

    Protein Dynamics and the Brain

    The brain is a molecular computer. How the brain computes, and feels and learns and remembers remain great mysteries. Neurobiologists have, however, identified some key protein actors in the mechanisms of learning and memory. I will describe some theoretical and computational efforts in understanding some of the molecular aspects of 1) Hebbian learning through the regulatable assembly of the actin cytoskeleton in dendritic spines, 2) the hypothesis that long-term memory involves a functional prion protein and 3) some aspects of the physical chemistry of aggregation processes that are involved in the pathogenesis of Huntington’s disease and Alzheimer’s disease. 

    Monday 10.08.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL


    Robert T. Sauer

    Department of Biology, Massachusetts Institute of Technology

    Protein recognition, unfolding, and translocation by the AAA+ ClpXP protease

    ClpX is a AAA+ unfoldase and translocase that works with the ClpP peptidase to perform ATP-dependent degradation of target proteins in organisms from bacteria to mammals. I will discuss cryo-EM structures of ClpXP with bound substrates, biochemical experiments, and single-molecule optical-trapping studies that provide insight into ClpXP mechanism.

    Monday 24.08.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Zoom:       Inactive



    Taekjip Ha

    Department of Biophysics, Johns Hopkins University

    Conformational Control: From Single Molecules to Biotechnologies

    Cellular functions of biological molecules are often controlled through conformational switching mediated by protein phosphorylation and protein-protein interactions. Single molecule biophysical studies of bacterial enzymes that unwind DNA in an ATP-dependent and ATP-independent manner taught us how their functions are controlled by conformational switching. We exploited these conformal control mechanisms to create new enzyme behaviors suitable for biotechnological applications (rapid pathogen detection, accurate genome-editing and genome imaging,…) and for new research avenues (co-transcriptional RNA folding, very fast DNA repair studies,…).

    Monday 07.09.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Zoom:       Inactive



    Matthias Rief

    Department of Physics, Technical University Munich

    Forces in Chaperone-Mediated Protein Unfolding and Cell Adhesion

    Many process in our cells are mechanical. Single molecule methods allow studying the forces involved in those processes. In my talk I will discuss 2 examples. In the first part, I will show how the concerted action of the hsp70 chaperone and its co-chaperones completely unfold the glucocorticoid receptor. In the second part of my talk, I will discuss how the cytoskeletal proteins talin and kindlin co-operate to strengthen their mechanical bond to the cell adhesion protein integrin.

    Monday 21.09.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL


    Monday 05.10.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Susan Marqusee

    Department of Molecular and Cell Biology, University of California Berkeley

    Modulation of the Energy Landscape by Cellular Factors

    The amino acid sequence of a protein encodes more than the native three-dimensional structure; it encodes the entire energy landscape – an ensemble of conformations whose energetics and dynamics are finely tuned for folding, binding, turnover, and function. Small variations in the sequence and environment modulate this landscape and can have effects that range from undetectable to pathological. I will present our recent results probing how cellular factors such as the ribosome, translation and ubiquitination affect the energetics and dynamics of a protein. 

    Zoom:       Inactive



    Monday 19.10.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Henry Chapman

    Deutsches Elektronen-Synchrotron DESY

    A Research Center of the Helmholtz Association

    Serial crystallography and diffraction with X-ray FELs

    Using X-ray free-electron laser pulses it is possible to outrun the effects of radiation damage, allowing room temperature measurements of macromolecular crystals at high resolution with a dose thousands of times higher than usually tolerable. Since an X-ray FEL pulse ultimately destroys the sample, measurements are carried out in a serial fashion, one sample at a time.  This has led to the paradigm of serial crystallography, requiring rapid sample delivery, high frame-rate detectors and software to aggregate data into what is essentially a three-dimensional powder diffraction pattern.  High-resolution room-temperature protein structures have been determined from crystals less than 0.01 micron^3 in volume, and high-resolution diffraction can be recorded from 2D macromolecular crystals or single fibrils. The method is especially useful for time-resolved crystallography, radiation-sensitive samples, small crystals, and studies of the dependence of structure on physical conditions and environments. The opportunities for this method have not been fully explored, and all aspects of the method are still under active development.  I will outline some of these opportunities and developments.

    Zoom:       Inactive



    Monday 02.11.

    8:00 PST -  11:00 EST - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Ivet Bahar

    Department of Computational and Systems Biology, University of Pittsburgh, School of Medicine

    Network models in biology: from molecular machinery and evaluation of missense variants, to chromosomal dynamics

    It is widely established that understanding protein dynamics is essential to bridging structure and function. One major challenge in computational modeling of protein dynamics is the computational cost and time required for viewing events of biological significance, the time scale and cooperative nature of which is often beyond the reach of conventional molecular dynamics simulations. Among coarse-grained models that have been developed for addressing this issue, elastic network models (ENMs) found wide usage in molecular biophysics and structural biology. The global motions predicted by ENMs have proven in numerous applications in the last two decades to provide a good description of molecular machinery and allosteric behavior complementing experimental data, despite the simplicity of the model and the lack of specificity. Application to supramolecular structures, including cryo-EM structures, has been a major utility of these models. More recently, ENMs proved useful to exploring chromosomal dynamics, using data from Hi-C experiments to reconstruct in silico the connectivity of the chromatin and provide a physical basis for gene regulation transcription and cell type differentiation. Finally, we will show how machine learning algorithms that incorporate ENM predictions provide an improved assessment of the effect of mutations on function, compared to those based on sequence and structure exclusively, and we discuss future directions.

    Recent Eaton Picture.jpg

    William A. Eaton

    NIH, NIDDK, Laboratory of Chemical Physics

    Modern Kinetics of Protein Folding; a Retrospective

    Modern kinetics of protein folding began in the early 1990’s with the introduction of nanosecond laser pulses to trigger the folding reaction, providing an almost 10^6-fold improvement in time resolution over the stopped-flow kinetic method being employed at the time. These experiments marked the beginning of the so-called “fast-folding” subfield that investigated the nanosecond-microsecond kinetics of protein structural elements for the first time, as well as the previously inaccessible kinetics of sub-millisecond folding proteins. Using single molecule spectroscopy, the microsecond time for crossing the free energy barrier separating folded and unfolded states (the transition path time) can now also be measured. I will trace the history of the fast-folding subfield using primarily results from my lab and provide a perspective on what I regard as the remaining outstanding problems in the kinetics and mechanism of protein folding.

    Monday 16.11.

    8:00 PST -  11:00 EST - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL


    Monday 30.11.

    8:00 PST -  11:00 EST - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Amnon Horovitz

    Department of Structural Biology, Weizmann Institute of Science

    Dissecting allosteric mechanisms and protein interactions using native mass-spectrometry

    Native mass spectrometry (MS) is an ideal method for studying allosteric systems because it provides a way for measuring the relative concentrations of many co-existing species.  Two applications of this approach will be described.  In the first one, I will show that native MS can be used to distinguish between the classical sequential and concerted allosteric models.  Distinguishing between these models has been difficult because ligand binding curves are insensitive to ligation intermediates.  Using native MS, it was possible to show that the chaperonin GroEL undergoes concerted intra-ring conformational changes.  In the second application, I will show that native MS can be used in conjunction with double-mutant cycles to determine the energetic coupling between residues involved in inter-protein interactions.  Coupling constants for the interaction between wild-type and ALS disease-causing mutant superoxide dismutase 1 subunits were measured using this approach and found to correlate with disease severity.


    Monday 14.12.

    8:00 PST -  11:00 EST - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Steven G. Boxer

    Department of Chemistry, Stanford University

    Electric Fields and Enzyme Catalysis

     We have developed the vibrational Stark effect to probe electrostatics and dynamics in organized systems, in particular in proteins where vibrational probes can report on functionally important electric fields. The strategy involves deploying site-specific vibrational probes whose sensitivity to an electric field is measured in a calibrated external electric field.  Once calibrated, these probes, typically nitriles or carbonyls, can be used to probe changes in electric field due to mutations, ligand binding, pH effects, light-induced structural changes, etc.  We can also obtain information on absolute fields by combining vibrational solvatochromism and MD simulations, checked by the vibrational Stark effect calibration.  This frequency-field calibration can be applied to quantify functionally relevantelectric fields at the active site of enzymes.  Using ketosteroid isomerase as a model system, we correlate the field sensed at the bond involved in enzymatic catalysis with the rate of the reaction it catalyzes, including variations in this rate in a series of mutants and variants using non-canonical amino acids. This provides the first direct connection between electric fields and function: for this system electrostatic interactions are a dominant contribution to catalytic proficiency.  Using the vibrational Stark effect, we can now consistently re-interpret results already in the literature and provide a framework for parsing the electrostatic contribution to catalysis in both biological and non-biological systems.  Extensions of this approach to other classes of enzymes, to effects of electrostatics on pathways of photoisomerization in proteins, and to the evolutionary trajectories of enzymes responsible for antibiotic resistance will be described if time permits.


    Monday 11.01.

    8:00 PST -  11:00 EST - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Michael Woodside

    Department of Physics, University of Alberta

    Observing misfolding and prion-like conversion in single protein molecules

    Protein misfolding is linked to a wide range of neurodegenerative diseases. In several of these diseases, misfolded isoforms of the disease-linked proteins are infectious, capable of converting natively folded molecules to make new copies of the misfolded isoform and thereby propagate the misfolding, as first seen in prion diseases. However, the mechanisms of prion-like misfolding remain unclear. I will present work using force spectroscopy to observe misfolding in single molecules of PrP and SOD1, related respectively to prion disease and ALS, exploring the mechanisms of misfolding and observing the templated conversion of single molecules into misfolded isoforms.  


    Monday 25.01.

    8:00 PST -  11:00 EST - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Marina Rodnina

    Max Planck Institute for Biophysical Chemistry, Goettingen

    The pathways of co-translational folding

    Protein domains start to fold co-translationally, while they are being synthesized on the ribosome. Co-translational folding is vectorial; it starts in the confined space of the polypeptide exit tunnel of the ribosome and is modulated by the speed of translation. Defects in protein folding cause many human diseases; thus, understanding the co-translational folding is of eminent importance. We mapped the pathways of co-translational folding for two proteins of different topology, a small five-helix domain HemK and a five-stranded beta-barrel protein CspA. In solution, both proteins fold by a concerted two-state mechanism. On the ribosome, HemK and CspA start to fold inside the exit tunnel and undergo several structural rearrangements that are not sampled in solution. HemK folds vectorially as soon as the N-terminal α-helical segments are synthesized. As nascent chain grows, consecutive helical segments dock onto each other and continue to rearrange at the vicinity of the ribosome. CspA forms compact non-native structures inside and at the vestibule of the exit tunnel and adopts the native fold only after the release from the ribosome. These results show how the ribosome defines the folding landscape of protein domains.

    Zoom:       Inactive



    Monday 08.02.

    8:00 PST -  11:00 EST - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Angela Gronenborn

    Department of Structural Biology, University of Pittsburgh

    Not so crystal clear - crystallins and cataract

    Cataracts are the leading cause of blindness in the world, with approximately 17 million cases per year. The disease is caused by protein aggregation in the eye lens, involving its major constituents, the crystallins. While the congenital form of the disease results from crystallin gene mutations, the age-related degenerative disease involves 'aged' crystallin proteins. Currently, the only available treatment is surgery, widely used in the developed world. However, access to surgery is not available to a significant fraction of the world population. Therefore, it is important to provide a structural understanding of cataract formation, if novel therapeutic approaches are to be developed to delay or slow the progression of cataracts. We are investigating the dynamics, structure and folding of human γD and bB crystallins, both WT and mutants that are associated with congenital or age-related cataract. We solved NMR and X-ray crystal structures of several variants and analyzed their dynamic behavior by solution NMR spectroscopy and SAXS. In this lecture I will report on our studies.

    Zoom:       Inactive



    Monday 01.03.

    8:00 PST -  11:00 EST - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Hagen Hofmann

    Department of Chemical and Structural Biology, Weizmann Institute of Science

    Allostery in DNA drives phenotype switching

    Allostery is a pervasive principle to regulate protein function. Here, we show that DNA also transmits allosteric signals over long distances to boost the binding cooperativity of transcription factors. Phenotype switching in Bacillus subtilis requires an all-or-none promoter binding of multiple ComK proteins. Using single-molecule FRET, we find that ComK-binding at one promoter site increases affinity at a distant site. Cryo-EM structures of the complex between ComK and its promoter demonstrate that this coupling is due to mechanical forces that alter DNA curvature. Modifications of the spacer between sites tune cooperativity and show how to control allostery, which paves new ways to design the dynamic properties of genetic circuits.


    Nozomi Ando

    Department of Chemistry and Chemical Biology, Cornell University

    Thinking outside of the lattice

    Correlated motions are essential for protein allostery and function, yet few experimental probes exist. In this talk, I’ll discuss how information on correlated atomic motions exists in the continuous background signal that is discarded in conventional X-ray crystallography. Despite its promise, however, this signal (known as diffuse scattering) has been very difficult to measure and interpret. I’ll discuss these historical challenges and the “making of” story behind our recent work as well as future outlook.

    Monday 08.03.

    8:00 PST -  11:00 EST - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Zoom:       Inactive



    Monday 22.03.

    9:00 PDT -  12:00 EDT - 16:00 UTC

    16:00 UK - 17:00 CET - 18:00 IL

    Joerg Enderlein

    III. Institute of Physics - Biophysics, Georg-August-University Goettingen

    Advanced Fluorescence Correlation Spectroscopy for 
    measuring molecular conformation and dynamics

    The development of single molecule spectroscopy (SMS) had an enormous impact on many biophysical studies by allowing to measure full distributions of molecular parameters, instead of only average values as usually determined by ensemble measurements. One specific technique of SMS is fluorescence correlation spectroscopy (FCS) which evaluates the fluorescence intensity fluctuations observed out of a femotliter-sized confocal detection volume. Thus allows to measure molecular size and concentration of fluorescently tagged molecule at pico- to nanomolar concentrations, but also to resolve conformational dynamics and conformational transitions with a temporal resolution down to a few nanoseconds. I will present a general introduction into FCS and will then focus on several of its advanced variants. In particular, I will introduce dual-focus or 2fFCS, which allows for precise calibration-free molecular sizing. Next, fluorescence lifetime correlation spectroscopy (FLCS) will be presented which is a powerful tool for resolving intramolecular conformational fluctuations. Then, I will discuss photoelectron transfer or PET-FCS, which is a simple but powerful complement to single-molecule Förster resonance energy transfer (smFRET) when studying conformational fluctuations in intrinsically disordered proteins. Finally, I will discuss FCS on a pico- to nanosecond timescale, where it provide valuable information about molecular rotational diffusion and molecular stoichiometry (fluorescence antibunching).


    Eugene I. Shakhnovich

    Department of Chemistry and Chemical Biology, Havard University

    Monday 05.04.

    8:00 PDT -  11:00 EDT - 16:00 UTC

    16:00 UK - 17:00 CEST - 18:00 IL

    Zoom:      Inactive


    Protein biophysics in the cellular context: physics meets evolution.

    I will present recent theoretical and experimental developments aimed at understanding the two-way link between protein stability and protein evolution.  At the heart of these developments are models of evolutionary dynamics that merge molecular mechanisms of protein stability and folding with population genetics. Traditional population genetics models are agnostic to the physical-chemical nature of mutational effects. Rather they operate with an a’priori assumed distributions of fitness effects (DFE) of mutations from which evolutionary dynamics are derived. Alternatively some population genetics models aim to derive DFE from evolutionary observations. In departure with this tradition the novel multiscale models integrate the molecular effects of mutations on physical properties of proteins, most notably their stability, into physically intuitive yet detailed genotype-phenotype relationship (GPR) assumptions. I will present a range of models from simple analytical diffusion-based model on biophysical fitness landscapes to more sophisticated computational models of populations of model cells where genetic changes are mapped into molecular effects using biophysical modeling of proteins and ensuing fitness changes determine the fate of mutations in realistic population dynamics. Examples of insights derived from biophysics-based multiscale models include parameter-free prediction of distribution of protein stabilities in natural proteomes that explains the observation of “marginal stability” of proteins without resorting to unproven stability-activity tradeoffs,  the fundamental limit on mutation rates in living organisms, physics of thermal adaptation, co-evolution of protein interactions and abundances in cytoplasm and related results, some of which I will present and discuss. 

    Next I will describe “bottom-up experimental efforts to establish the relationship between biophysical properties of proteins (stability, activity, interactions with other proteins) and fitness. The approach is based on introducing rational introducing genetic variation on the chromosome of E.coli using genome editing approaches with subsequent concurrent evaluation of biophysical effects of mutations in vitro and fitness effect of strains that have these genetic variants in their chromosome. Carrying out this program for two genes encoding essential metabolic enzymes in E. coli – folA and adk – we obtained deep insights into the relationship between protein stability and fitness. In particular we quantitatively determined how the changes in stability affect the protein turnover in cellular environment resulting in changes in the abundance of functional protein and through that affecting the phenotype (growth rates and lag times). We established fundamental role of protein quality control – chaperone GroEL and certain proteases that modulate the fitness effects of stability-changing mutations in a predictable way. We developed a dynamic steady state theory that describes stability-dependent protein turnover and established the relationship between protein abundance and stability that is different from simple equilibrium Boltzmann distribution. These advances allowed us to get a comprehensive biophysical fitness landscapes for metabolic enzymes. Further we applied these advances to the analysis of antibiotic resistance in DHFR encoded by folA. The theory allowed predicting fitness effect of escape mutations in DHFR and IC50 against antibiotic trimethoprim with very high accuracy based only on biophysical molecular properties of numerous DHFR mutants. Altogether these results provide a clear picture of interplay between biophysical traits and evolutionary dynamics on various time scales – from evolution of modern proteomes to evolution of antibiotic resistance and provides practical tools to address the problem of pathogen escape from stressors from a fundamental physical-chemical perspective.


    Monday 19.04.

    8:00 PDT -  11:00 EDT - 16:00 UTC

    16:00 UK - 17:00 CEST - 18:00 IL

    José Nelson Onuchic

    Center for Theoretical Biological Physics and Departments of Physics

    and Astronomy, Chemistry, and Biosciences

    Rice University

    Protein sequence coevolution, energy landscapes and their connections to structural maintenance of chromosomes (SMC) proteins

    Energy landscape theory has been a powerful approach to study protein folding dynamics and function. The discovery that an accurate estimate of the joint probability distribution of amino acid occupancies in protein families provides insights about residue-residue coevolution and concrete details about protein folding landscapes has also advanced structural biophysics. Our realization that the collection of couplings and local fields as parameters of such distribution is inherently connected with the thermodynamics of sequence selection towards folding and function demonstrates the importance of coevolutionary methods to understand stability and function of biomolecules.  The synergy between structure based models and coevolutionary information has spearheaded the field of structure prediction, including protein and RNA, as well as accelerating the discovery of functional structural states and the prediction of protein complexes. Coevolution signals can also be used to create protein recognition metrics, which led to successful experimental efforts, and the uncovering of novel molecular interactions. This idea has opened the door to encode recognition in protein pairs. Recently this approach has been used to predict extremely large protein assemblies consisting of structural maintenance of chromosomes (SMC) and kleisin subunits which are essential for the process of chromosome segregation across all domains of life. While limited structural data exist for the proteins that comprise the (SMC)–kleisin complex, using an integrative approach combining both crystallographic data and coevolutionary information, we predicted an atomic-scale structure of the whole condensing complex in prokaryotes. Also, leveraging coevolutionary sequence information and molecular simulations with an energy landscape optimized force field, we not only developed complete structural models of several kleisin complexes in different organisms but also their motions. The coiled-coil regions of these complexes braid together. Braiding is controlled by the head domains, which are ATPase motors.


    Robert B. Best

    NIH, NIDDK, Laboratory of Chemical Physics

    From disordered proteins to complexes and assemblies


    Intrinsically disordered proteins are challenging to characterize by experiment owing to the diverse ensemble of structures they populate. This gives molecular simulations a powerful role as a natural complement to experiment. I will discuss how molecular simulations can be integrated with experiments to yield new insights into the properties of individual IDP chains and their complexes with other intrinsically disordered proteins and nucleic acids. Lastly, I will talk about our work developing coarse-grained models to describe phase separation to form biomolecular coacervates.

    Monday 03.05.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT


    Monday 17.05.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT

    Brian Dyer

    Department of Chemistry, Emory University

    Protein mediated membrane fusion studied by time resolved spectroscopy

    The molecular basis of transmission and pathogenesis of the influenza virus is incompletely understood. Key early steps in the viral infection process involve acidification of the viral lumen by the M2 proton channel and membrane fusion mediated by hemagglutinin. These coordinated events are triggered by the low pH of the endosome and together facilitate release of the viral contents into the cytosol of the host cell. M2 is a highly selective and unidirectional proton channel that is activated at low pH, switching on proton conductance and acidifying the viral lumen to enable release of the viral ribonucleoproteins. While the structure of M2 has been determined at neutral and low pH, the dynamics that activate proton conductance are not known. The second essential step of infection is the formation of a fusion pore, mediated by the viral coat protein hemagglutinin (HA). Hemagglutinin has served as an archetype for understanding the general mechanism of membrane fusion and it is also an important target for antiviral drug development. HA is postulated to undergo an astounding series of refolding reactions triggered by lowered pH. The proposed spring-loaded mechanism of HA mediated membrane fusion has been inferred from equilibrium structures of pre- and post-fusion states, despite the highly dynamic nature of its pH dependent structure. As a consequence, the molecular details of HA mediated membrane fusion are not known, particularly with respect to the protein-membrane interactions. We have explored the molecular mechanism of HA mediated membrane fusion and M2 mediated proton transport that enable influenza virus infection, using time-resolved infrared and fluorescence spectroscopies of these proteins reconstituted in lipid vesicles. We have characterized the functional dynamics of HA and M2 induced by low pH using the laser pH-jump as a trigger and time resolved spectroscopy to map the structural dynamics.


    Monday 31.05.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT

    Peter Hamm

    Department of Chemistry, University of Zurich

    A Nonequilibrium Approach to Allosteric Communication

    With the term "allostery" one describes the coupling of two separated sites of a protein, where binding of a ligand at the so-called allosteric site changes the function of the protein at a remote active site. Allostery is one of the fundamental mechanisms of regulatory processes in life. The very question of how these two sites communicate with each other remains an intriguing and controversial problem, with the ultimate question of how an allosteric signal ``propagates'' through a protein. Transient IR spectroscopy provides the time resolution combined with the chemical selectivity necessary to study these nonequilibrium processes. In these experiments, an allosteric protein is light-trigger with the help of a photo-isomerizing azobenzene moiety, which is incorporated into the protein in a way that it mimics an allosteric process, and the response of the protein is recorded by transient IR spectroscopy. I will discuss a variety of protein systems that we have designed for that purpose, as well as ongoing experiments. 

    Zoom:      Inactive


    Elizabeth Rhoades

    Department of Chemistry, Penn Arts & Sciences

    It takes tau to tangle:  functional studies of a dysfunctional protein

    Tau is an intrinsically disordered neuronal protein which is thought to have a role in stabilizing axonal microtubules. We are interested in understanding the tau’s functional mechanisms as relevant to the unique properties of axonal microtubules. Here, we use single molecule fluorescence and fluorescence correlation spectroscopy to characterize the interactions of tau with soluble tubulin.  We identify a novel tubulin-binding domain of tau and demonstrate that it  that it is independently capable of polymerizing tubulin into microtubules. We propose a model for tau function which highlights the role of this novel domain.

    Monday 14.06.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT


    Joan-Emma Shea

    Department of Chemistry and Biochemistry, Department of Physics, UCSB

    Fibrillization and Liquid-Liquid Phase Separation of the Tau Peptide 

    Intrinsically disordered peptides (IDP) are a special class of proteins that do not fold to a unique three-dimensional shape. These proteins play important roles in the cell, from signaling to serving as structural scaffolds. Under pathological conditions, they can self-assemble into structures that are toxic to the cell, and a number of neurodegenerative diseases are associated with this self-assembly process. My talk will focus on the Tau protein, an IDP that binds to microtubules and can form fibrillar aggregates, a process that has been linked with Alzheimer’s disease. In addition to forming fibrils, the Tau protein can also phase separate into a protein rich and a protein depleted phase, a process known as liquid-liquid phase separation (LLPS). This process may play a protective role in the cell against pathological fibrillization. I will present molecular dynamics and field theoretic simulations that map out the phase diagram for Tau LLPS, and use this phase diagram to predict the conditions under which Tau can be driven towards LLPS under cellular conditions. 

    Monday 28.06.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT

    Zoom:       Inactive


    Rohit Pappu

    Department of Biomedical Engineering, Center for Science & Engineering of Living Systems, Washington University in St. Louis

    Emergent structures, functions, and phase behavior driven by charge-rich disordered proteins 

    This talk will focus on new findings that have emerged from our studies of disordered proteins that are enriched in ionizable residues. Features such as differences in Lys vs. Arg contents, charge regulation of Glu-rich regions, the interplay between acidic groups and polar moieties, and the blocky patterning of Lys / Glu rich regions give rise to rich complexities across multiple length scales. The talk will highlight physical principles underlying the evolutionarily conserved sequence features of charge-rich regions, their roles in dictating the functions of polymerizing enzymes, the regulation of thermoresponsive phase transitions, and in determining the compositional specificity of biomolecular condensates. 

    Monday 12.07.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT

    Zoom:       Inactive

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    Monday 26.07.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT

    Mei Hong

    Department of Chemistry, Massachusetts Institute of Technology (MIT)

    Structure and Dynamics of Membrane Proteins in Infectious Diseases 

    Viroporins are small ion channels that are important for the lifecycle and pathogenicity of many enveloped viruses. Elucidating their structure, dynamics and mechanism of action is important for our fundamental understanding of ion channels and for designing channel inhibitors as antiviral drugs. Using solid-state NMR spectroscopy, we have obtained rich insights into the proton conduction mechanism of influenza virus M2 proteins. These insights come from measurement of the proton transfer equilibria and rates of a crucial histidine residue in M2 when bound to cholesterol-containing lipid bilayers. We also measured water dynamics and water orientations in closed and open M2 channels, giving complementary information about the mixed hydrogen-bonded chain between water and histidine for proton transport in these channels. Applying solid-state NMR, we recently determined the structure of the SARS-CoV-2 envelope (E) protein, the equivalent viroporin in coronaviruses. The five-helix bundle structure shows the binding site of the inhibitor hexamethylene amiloride, and provides a framework for understanding the cation conduction mechanism of E.

    Clore photo no copyright.jpg

    Monday 09.08.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT

    Marius Clore

    NIH, NIDDK, Laboratory of Chemical Physics

    Probing transient pre-nucleation oligomerization of huntingtin at atomic resolution by NMR

    Huntington’s disease is a fatal, autosomal, neurodegenerative condition that arises from CAG expansion within exon-1 of the huntingtin gene that encodes a polyglutamine (polyQ) repeat.  Although the huntingtin protein is very large (~350 kDa), proteolysis and/or incomplete mRNA splicing generates mutated N-terminal fragments encoded by exon-1 that aggregate to form neuronal inclusion bodies in pathological states. The N-terminal region of huntingtin encoded by exon 1, httex1, comprises three distinct regions or domains: a 16-residue N-terminal amphiphilic sequence (httNT), a polyQ tract of variable length, and a proline rich domain (PRD) with two polyproline repeats of 11 (P11) and 10 (P10) residues. In this talk we will summarize out work on the earliest pre-nucleation transient oligomerization events involving httex1 using NMR experiments designed to probe rapidly exchanging systems (sub-millisecond time range) involving sparsely-populated excited states. We show that a branched assembly mechanism is involved comprising on- and off-pathways. In the on-pathway branch, the major monomeric species self-associates to form a productive helical coiled-coil dimer of the NT region that goes on to form a four-helix bundle tetramer comprising a dimer-of-dimers. In the off-pathway branch, a “non-productive” dimer ensemble with partially helical character is formed that does not undergo further oligomerization. The importance of pre-nucleation tetramerization is evidenced by the fact that inhibition of tetramer formation blocks fibrillization. Thus on-pathway tetramerization constitutes the prenucleation trigger or molecular switch that hugely increases the probability of occurrence of intermolecular polyQ contacts (by effectively increasing the local concentration of the polyQ tracts) and hence polyQ fibril formation.  It is therefore clear that blocking productive dimer and/or tetramer formation may provide a fruitful avenue for preventing or delaying the onset of Huntington’s disease. Inhibition of pre-nucleation oligomerization can be achieved in a number of ways: (a) perturbing the productive dimer and/or tetramer interface; (b) sequestration of httex1 through binding of the httNT sequence to chaperones; and (c) allosteric, long-range inhibition by interaction of intracellular proline-binding proteins with the proline rich domain (PRD).

    Zoom:       Inactive


    Monday 23.08.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT

    Dmitrii E. Makarov

    Department of Chemistry and Oden Institute for Computational Engineering and Sciences, University of Texas at Austin

    How I plan to study protein folding and dynamics by proving theorems 

    Biophysicists visualize biomolecular folding as motion along one-dimensional “folding coordinates” (aka “reaction coordinates” or “order parameters”) over free energy barriers. Various rate theories, such as transition state theory and Kramers’ theory of diffusive barrier crossing, differ in their assumptions regarding the mathematical specifics of this motion. Direct experimental observation of the motion along reaction coordinates requires single-molecule experiments performed with unprecedented time resolution. Toward this goal, recent single-molecule studies achieved time resolution sufficient to catch biomolecules in the act of crossing free energy barriers as they fold, bind to their targets, or undergo other large structural changes, offering a window into the elusive folding/binding/reaction  “mechanisms”. In this talk, I will discuss how one can use these emerging data to answer several questions of principle. For example, is motion along the folding reaction coordinate diffusive, how heterogeneous is the ensemble of paths leading from the unfolded to the folded state, is there conformational memory, and is reduction to just one degree of freedom to represent the folding mechanism justified? I will show how these questions can be formulated as strict, experimentally testable mathematical inequalities and illustrate their utility in application to experimental and atomistic simulation data. No math beyond freshmen calculus is needed to understand this talk. 

    Zoom:       Inactive


    Monday 04.10.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT

    Peter E. Wright

    Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA

    Role of dynamic protein disorder in the regulation of cellular signaling

    Intrinsically disordered proteins (IDPs) and protein regions (IDRs) are highly abundant in the human proteome and are strongly associated with numerous devastating diseases, including cancers, age-related neurodegenerative disorders, diabetes, cardiovascular and infectious diseases. IDPs mediate critical regulatory functions in the cell, including transcription, translation, the cell cycle, and numerous signal transduction events. The unique features of IDPs and IDRS – lack of stable structure, dynamics, accessibility to posttranslational modification, multiplicity of interaction motifs – confer numerous functional advantages, allowing IDPs and IDRs to exert an exquisite level of control over cellular signaling pathways. The role of IDPs and IDRs in dynamic cellular signaling will be discussed with reference to regulation of DNA binding by p53 and the mechanism of a unidirectional, hypersensitive allosteric switch that downregulates the hypoxic response by displacing the hypoxia inducible factor HIF-1α from the general transcriptional coactivators CBP (CREB binding protein) and p300.


    Monday 18.10.

    8:00 PDT -  11:00 EDT - 15:00 UTC

    16:00 BST - 17:00 CEST - 18:00 IDT

    Victor Muñoz

    Department of Bioengineering, School of Engineering, University of California, Merced

    Molecular mechanisms for gene tracking in eukaryotic transcription: Single-molecule analysis of the interplay between DNA recognition and folding of homeodomains 

    Transcription factors (TF) control gene expression by binding to their target DNA site to recruit, or block, the transcription machinery onto the promoter region of the gene of interest. Their function relies on the ability to find their target site quickly and selectively. The classical mechanism for such tracking is based on two DNA binding modes: high affinity specific to the target site and low-affinity non-specific (sequence independent). Non-specific binding competes for the TF’s occupancy by sheer numbers, but also enables the TF to slide along DNA resulting on facilitated diffusive search for the target along just one dimension. The TF can also transfer between DNA regions in transient spatial proximity as additional search-facilitating mechanism. These elements suffice to explain the homing, selectivity, and occupancy of prokaryotic TFs in living cells. In eukaryotes transcription control is much more complex, and operates in multiple layers, including dynamic control over the chromatin structure and epigenetic factors. However, even at the molecular level there are big unsolved puzzles. For instance, the DNA binding domains (DBD) of eukaryotic TFs recognize much shorter specific sequences (6-10 bp), but the genomes are orders of magnitude longer and hence contain thousands of randomly occurring, competing consensus sites. In addition, eukaryotic DBDs, and particularly homeodomains, are predicted to be intrinsically disordered based on their sequence and found to be flexible and highly dynamic in folding studies, which hints at a possible role for protein disorder in the DNA recognition process. Yet, these DBDs seem to form the same unique 3D structure when alone (by NMR) and bound to DNA (by X-ray crystallography). 


    In my laboratory we are addressing these molecular puzzles using single-molecule methods and the homeodomain from the eukaryotic TF Engrailed (EHD) as model system. Particularly, we are carefully mapping out the folding properties and DNA binding and diffusive behavior of EHD, both at the local level (<50 bp) and in the context of full genes using a combination of advanced sm-FRET methods, optical tweezers coupled to confocal fluorescence microscopy, and computer simulations. In this talk I will provide an overview of our prior work on the discovery of promiscuous DNA binding and transcription antennas, and on the identification of a disordered-enabled fast DNA gliding mode. I will also discuss some of our most recent results in support of a conformational rheostat mechanism for efficiently reading out the DNA sequence.    


    Monday 01.11.

    9:00 PDT -  12:00 EDT - 16:00 UTC

     17:00 CET - 18:00 IST - 0:00 CST

    Kresten Lindorff-Larsen

    Structural Biology and NMR Laboratory, Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen

    Interpreting experiments using simulations and using experiments to improve simulations of intrinsically-disordered proteins

    Intrinsically disordered proteins (IDPs) and flexible regions in multi-domain proteins display substantial conformational heterogeneity. Characterizing the conformational ensembles of these proteins in solution typically requires combining data from one or more biophysical techniques with computational modelling or simulations. Experimental data can either be used to assess the accuracy of a computational model or to refine the computational model to get a better agreement with the experimental data. I will discuss two different approaches to integrate experiments and simulations of IDPs.

    In the first approach we use experimental data to refine conformational ensembles of IDPs in a system-specific manner. I will describe how we use our Bayesian-Maximum Entropy software to refine conformational ensembles of IDPs generated by simulations. I will briefly touch upon a key issue regarding the so-called “forward models” that are used to calculate experimental observables from conformational ensemble and highlight how generating such models for IDPs is important but difficult.

    In the second approach we use the experimental data to refine the force field used the simulations. I will describe a Bayesian formalism we have developed and applied to optimize and parameterize force fields by targeting experimental observables. We have used this method to parameterize a new coarse- grained model for IDPs by targeting data from small-angle scattering experiments and nuclear magnetic resonance spectroscopy on IDPs in solution. I will describe how this model enables us to study interactions between IDPs and their formation of higher-order structures in biomolecular condensates, and discuss initial work towards improving the Martini coarse-grained model for disordered proteins.


    Seminar starts an hour later than usual.

    Monday 22.11.

    9:00 PST -  12:00 EST - 17:00 UTC

     18:00 CET - 19:00 IST - 1:00 CST

    Helmut Grubmüller

    Department of Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry, Goettingen

    Microtubules’ bends, cryo-cool ribosomes, and wet proteins

    In this talk we will survey some of our current work on large biomolecular systems and new methods for atomistic simulations.

    In the first part, we will address the mechanochemical basis of microtubule growth and shortening, driven by GTP hydrolysis -- specifically: Why do post-hydrolysis microtubules not grow? Through non-equilibrium atomistic simulations of entire plus-end microtubule tips we show that the average nucleotide state of the plus-end MT tip determines the heights of energy barriers between tip conformations, such that the post-hydrolysis MT tip is exposed to higher activation energy barriers, which translates into its inability to elongate.

    The second part addresses the question: How much of the ambient temperature ensemble of biomolecules is preserved during cryo-electron microscopy shock freezing? In shock cooling atomistic simulations of fully solvated ribosomes at realistic time scales we observed, depending on cooling rates, a marked decrease of structural heterogeneity. The observation that a kinetic two-state model improves the prediction of the decrease in heterogeneity compared to the cooling-rate independent thermodynamic model suggests that kinetic effects do contribute markedly. Small barriers between the states (<10 kJ/mol) are overcome during cooling and do not contribute to the heterogeneity of the structural ensemble obtained by cryo-EM, whereas conformational states separated by barriers above 10 kJ/mol are expected to be trapped during plunge-freezing. Our results will allow one to quantify the heterogeneity of biologically relevant room-temperature ensembles from cryo-EM structures.

    We will, in the third part, quantify the enthalpy/entropy tug-of-war of the first few solvent layers of proteins. Effects such as cold denaturation of proteins show that the solvent shell contributes decisively to protein stability. For the example protein crambin, we quantified the local effects on the solvent free-energy difference at each amino acid and identified strong dependencies of the local enthalpy and entropy on the protein curvature. Remarkably, more than half of the solvent entropy contribution arises from induced water correlations.


    Monday 06.12.

    8:00 PST -  11:00 EST - 16:00 UTC

     17:00 CET - 18:00 IST - 0:00 CST

    Martin Blackledge

    Protein dynamics and flexibility by NMR, Institut de Biologie Structurale UGA-CEA-CNRS, Grenoble, France

    Complex dynamics and dynamic complexes: NMR studies of highly dynamic viral replication assemblies

    Proteins are inherently dynamic, exhibiting conformational freedom on many timescales, implicating structural rearrangements that play a major role in molecular interaction, thermodynamic stability and biological function. Intrinsically disordered proteins (IDPs) represent extreme examples where flexibility defines molecular function. In spite of the ubiquitous presence of IDPs throughout biology, the molecular mechanisms regulating their interactions remain poorly understood. We use NMR spectroscopy to develop a unified description of the dynamics of IDPs as a function of environmental conditions, and to map these complex molecular recognition trajectories at atomic resolution, from the highly dynamic free-state equilibrium to the bound state ensemble.

    Examples include the nuclear pore, where weak interactions between the nuclear transporter and highly flexible chains containing multiple ultra-short recognition motifs, facilitate fast passage into the nucleus, and the replication machinery of Measles virus, where we use NMR to characterize the 92 kDa complex formed between the highly disordered phosphoprotein and the nucleoprotein prior to nucleocapsid assembly – a process that we can also follow in real-time. These proteins undergo liquid-liquid phase separation upon mixing and we are currently using NMR and fluorescence to describe the molecular basis and functional advantages of this phenomenon. NMR also shed new light on the molecular basis of host adaptation of influenza polymerase, via a highly dynamic interaction.


    Monday 20.12.

    8:00 PST -  11:00 EST - 16:00 UTC

     17:00 CET - 18:00 IST - 0:00 CST

    Birthe Kragelund

    Department of Biology, University of Copenhagen

    Folding and binding in context

    Complex formation between proteins where one partner is intrinsically disordered is often associated with folding, but the degree of folding varies depending on the complex type and the interactions involved, and even fully disordered complexes exist. Interactions by intrinsically disordered proteins are in many cases driven by conserved short linear motifs, SLiMs, and emerging studies have shown that the disordered flanking regions surrounding the SLiM can contribute both positively and negatively to binding. Focusing on two different folded hub domains that each interacts with a large set of disordered binding partners, we have addressed how and in which ways context contribute to binding. In particular, we find that temperature dependent ITC, embedded in an intrinsically disordered-optimized Spolar-Record (SRID) approach combined with NMR spectroscopy provides complementary methods to deciphering context properties and contributions to binding.


    Monday 31.01.

    8:00 PST -  11:00 EST - 16:00 UTC

     17:00 CET - 18:00 IST - 0:00 CST

    Felix Ritort

    Small Biosystems Lab, Departament de Física de la Matèria Condensada, Facultat de Física, Universitat de Barcelona

    Calorimetric force spectroscopy of nucleic acids and proteins

    DNA, RNA, and proteins are polymers that fold into three-dimensional structures to perform their biological function. How these molecules fold is, however, not fully understood. Although some models advocate for funnel-like energy landscapes, others envision folding as a cooperative process mediated by the sequential formation of intermediates. In this talk, I introduce calorimetric force spectroscopy in a temperature jump optical trap as a powerful tool to understand the folding of nucleic acids and proteins. While cooperativity in nucleic acids arises from base stacking interactions in proteins, it is determined by the low configurational entropy of the transition state along the folding pathway. Here, I show how accurate measurements of heat capacity changes during the folding of protein barnase permit us to characterize the transition state's enthalpy, entropy, and heat capacity. We find that the transition state has the properties of a molten globule, i.e., high-free energy and low configurational entropy, being structurally similar to the native state.

    Zoom:       Inactive


    Monday 14.02.

    8:00 PST -  11:00 EST - 16:00 UTC

     17:00 CET - 18:00 IST - 0:00 CST

    Ad Bax

    NIH, NIDDK, Laboratory of Chemical Physics

    Folding and misfolding of polypeptides probed by simple and more advanced NMR experiments  


    Chemical denaturation is a well-established approach for shifting the equilibrium between folded and unfolded states of globular proteins. However, as demonstrated for Ab1-42 the approach is equally suitable for identifying small populations of transiently folded structural element in IDPs.  More interesting are experiments that rapidly and reversibly shift the thermodynamic equilibrium between folded and unfolded states of a protein by jumping the hydrostatic pressure.  As demonstrated for ubiquitin, NMR experiments then can provide detailed structural information on transient on-pathway folding intermediates, and they can be used to probe the properties of misfolded oligomeric states of systems such as Ab.


    Monday 14.03.

    9:00 PDT -  12:00 EDT - 16:00 UTC

     17:00 CET - 18:00 IST - 0:00 CST

    David Nesbitt

    Joint Institute for Laboratory Astrophysics (JILA), University of Colorado Boulder

    Kinetics and Thermodynamics of Nucleic Acid Folding: Temperature/Pressure Dependent Studies at the Single Molecule Level


    The ability to look with laser microscopy at single biomolecules has led to a revolution in research opportunities for chemistry, physics and molecular biology. This talk will present three examples of recent activities from our group, all with the common theme of confocal microscopy, fluorescence resonance energy transfer (FRET), and single photon counting methods for single molecule kinetics and thermodynamics of conformational RNA folding into competent biostructures. As a first example, exquisite temperature control in single molecule “nanobathtubs” is used to allow systematic deconstruction of free energies landscapes (DG0) into enthalpic (DH0) and entropic (-TDS0) components, as well as elucidate properties of transition state barriers (e.g., DH‡, DS‡) for folding/unfolding. A second topic is the effect of molecular “crowding” on RNA/DNA loop/stem formation and hybridization at the single molecule level, in order to explore conditions relevant to in vivo crowding in the cellular cytoplasm. Finally, I will discuss recent extensions of these methods into the kinetics and thermodynamics of folding/unfolding at high hydrostatic pressures (Pext = 1-4000 bar), which allows one to interrogate the impact of sequence, mono/divalent cations, ligands, osmolytes, etc. on stabilities and free volumes (DV0DV‡) for nucleic acid folding. One unifying goal is to provide quantitative thermodynamic and kinetic data for benchmark comparison with theoretical predictions, as well as the development of simple physical models to help interpret, explain, and potentially control the underlying biophysics of nucleic acid folding at the single molecule level.


    Monday 11.04.

    8:00 PDT -  11:00 EDT - 15:00 UTC

     17:00 CEST - 18:00 IST - 23:00 CST

    Catherine Royer

    Biological Sciences, Rensselaer Polytechnic Institute

    Pushing proteins into excited states: Structural, energetic and dynamic mapping of protein conformational landscapes using high pressure


    The mechanisms underlying biomolecular function often implicate structurally “excited” states that are higher in energy and less ordered than those observed in crystallographic studies. Characterization of functionally relevant excited states in terms of their conformations, energetics and dynamics is necessary for understanding and for modulating function. Hydrostatic pressure has proven useful towards this end as it destabilizes biomolecular structure due to differences in system volume between ordered and disordered states, leading to the population of protein excited states. Coupling pressure perturbation with NMR, fluorescence, small angle x-ray scattering and simulations allows for their characterization. We have applied this approach on a model leucine-rich repeat protein domain, pp32, to map its conformational and energetic landscape, and to assess the consequences of the destabilizing introduction of cavities in different structural contexts. More recently we have begun to apply this approach to a family of small GTPases, the Arf proteins, with the goal of tracing their GDP/GTP switch transitions, and revealing the molecular basis for their functional specificity.


    Monday 16.05.

    8:00 PDT -  11:00 EDT - 15:00 UTC

     17:00 CEST - 18:00 IST - 23:00 CST

    Gabriela Schlau-Cohen

    Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts

    Why don't plants get sunburn?


    In photosynthesis, chlorophyll-containing proteins capture solar energy and funnel it to the downstream molecular machinery. In green plants, excess energy absorbed beyond the capacity of this molecular machinery can cause damage. Thus, plants have evolved a feedback loop that triggers photoprotective energy dissipation under high light (i.e., sunny days), solving the so-called “intermittency problem” in solar energy but at the expense of overall biomass production. While many open questions remain about the mechanism of dissipation, a long-standing proposal has been that conformational changes of the photosynthetic proteins are responsible for activating dissipative photophysical pathways in the chlorophyll. However, these conformations are difficult to resolve in ensemble measurements, which average over all proteins and their dynamics. Using single-molecule spectroscopy, we identified and characterized two distinct photoprotective conformational changes that switched photosynthetic proteins into dissipative conformations. We found that the equilibrium for one of the conformational changes is controlled in response to fast changes sunlight and the equilibrium for the other is controlled in response to slow increases. Thus, the multi-timescale protein dynamics can regulate energy on the multiple timescales of fluctuations in solar intensity.  

    Zoom:       Inactive


    Monday 13.06.

    8:00 PDT -  11:00 EDT - 15:00 UTC

     17:00 CEST - 18:00 IST - 23:00 CST

    Michele Vendruscolo

    Department of Chemistry, University of Cambridge

    Protein aggregation kinetics and its application to drug discovery for protein misfolding diseases 


    The process of protein aggregation is linked to a wide range of human disorders that include Alzheimer’s and Parkinson’s diseases. The oligomeric intermediates produced during this process are increasingly recognized as highly cytotoxic. It has been very challenging, however, to target these oligomers with therapeutic compounds, because of their dynamic and transient nature. To overcome this problem, I will describe a kinetics-based approach, which enables the discovery and systematic optimization of compounds that reduce the number of oligomers produced during an aggregation reaction. I will illustrate this strategy for the amyloid beta peptide, which is closely associated with Alzheimer's disease. As this strategy is general, it can be applied to oligomers of other proteins in drug discovery programmes. 

    Zoom:       Inactive


    Monday 11.07.

    8:00 PDT -  11:00 EDT - 15:00 UTC

     17:00 CEST - 18:00 IST - 23:00 CST

    Roland R. Netz

    Department of Physics, Free University Berlin, Germany

    Non-Markovian modeling of protein folding 


    Protein-folding kinetics is often described as Markovian (i.e., memoryless) diffusion in a one-dimensional free energy landscape, governed by an instantaneous friction coefficient that is fitted to reproduce experimental or simulated folding times. For a few different examples, I demonstrate that the friction extracted from molecular dynamics simulations exhibits significant memory with a decay time that is of the same order as the folding and unfolding times. Non-Markovian modeling not only reproduces the molecular dynamics simulations accurately but also demonstrates that memory friction effects lead to anomalous and drastically modified protein kinetics.


    Thomas Perkins

    Department of Molecular, Cellular, and Developmental Biology, University of Colorado Boulder

    Probing the energetics and hidden dynamics of bacteriorhodopsin by AFM


    The forces and energetics that stabilize membrane proteins remain elusive to precise quantification. Single-molecule force spectroscopy can yield kinetic rate constants, energetics, intermediate states, unfolding pathways, and even a projection of the underlying free-energy landscape. Using recently developed micromachined AFM cantilevers, we reexamined the unfolding of individual molecules of bacteriorhodopsin (bR) embedded in its native lipid bilayer with a 100-fold improvement in time resolution and a 10-fold improvement in force precision. Numerous newly detected intermediates—many separated by as few as 2–3 amino acids—exhibited complex dynamics, including frequent refolding and state occupancies of <10 µs. Rapid and reversible dynamics in the initial unfolding of bR allowed us to measure the equilibrium energetics of a membrane protein in its native lipid bilayer, an advance over traditional results obtained by chemical denaturation in nonphysiological mixed micelles.

    Monday 15.08.

    8:00 PDT -  11:00 EDT - 15:00 UTC

     17:00 CEST - 18:00 IST - 23:00 CST

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