Searching for Structure: Characterizing the Protein Conformational Landscape with Clustering-Based Algorithms.

Proteins with intrinsically disordered regions (IDRs) have large hydrodynamic radii, compared with globular proteins of equivalent weight. Recent experiments showed that IDRs with large radii can create steric pressure to drive membrane curvature during Clathrin-mediated endocytosis (CME). Epsin and Eps15 are two CME proteins with IDRs that contain multiple motifs for binding the adaptor protein AP2, but the impact of AP2-binding on these IDRs is unknown. Some IDRs acquire binding-induced function by forming a folded quaternary structure, but we hypothesize that the IDRs of Epsin and/or Eps15 acquire binding-induced function by increasing their steric volume. We explore this hypothesis in silico by generating conformational ensembles of the IDRs of Epsin (4 million structures) or Eps15 (3 million structures), then estimating the impact of AP2-binding on Radius of Gyration (RG). Results show that the ensemble of Epsin IDR conformations that accommodate AP2 binding has a right-shifted distribution of RG (larger radii) than the unbound Epsin ensemble. In contrast, the ensemble of Eps15 IDR conformations has comparable RG distribution between AP2-bound and unbound. We speculate that AP2 triggers the Epsin IDR to function through binding-induced-expansion, which could increase steric pressure and membrane bending during CME.

Structural Ensembles of Intrinsically Disordered Proteins using Molecular Dynamics Simulation

Salts modulate the behavior of intrinsically disordered proteins (IDPs) and influence the formation of membraneless organelles through liquid-liquid phase separation (LLPS). In low ionic strength solutions, IDP conformations are perturbed by the screening of electrostatic interactions, independent of the salt identity. In this regime, insight into the IDP behavior can be obtained using the theory for salt-induced transitions in charged polymers. However, salt-specific interactions with the charged and uncharged residues, known as the Hofmeister effect, influence IDP behavior in high ionic strength solutions. There is a lack of reliable theoretical models in high salt concentration regimes to predict the salt effect on IDPs. We propose a simulation methodology using a coarse-grained IDP model and experimentally measured water to salt solution transfer free energies of various chemical groups that allowed us to study the salt-specific transitions induced in the IDPs conformational ensemble. We probed the effect of three different monovalent salts on five IDPs belonging to various polymer classes based on charged residue content. We demonstrate that all of the IDPs of different polymer classes behave as self-avoiding walks (SAWs) at physiological salt concentration. In high salt concentrations, the transitions observed in the IDP conformational ensembles are dependent on the salt used and the IDP sequence and composition. Changing the anion with the cation fixed can result in the IDP transition from a SAW-like behavior to a collapsed globule. An important implication of these results is that a suitable salt can be identified to induce condensation of an IDP through LLPS.

The conformational ensemble and function of intrinsically disordered proteins (IDPs) are sensitive to their solution environment. The inherent malleability of disordered proteins combined with the exposure of their residues accounts for this sensitivity. One context in which IDPs play important roles that is concomitant with massive changes to the intracellular environment is during desiccation (extreme drying). The ability of organisms to survive desiccation has long been linked to the accumulation of high levels of cosolutes such as trehalose or sucrose as well as the enrichment of IDPs, such as late embryogenesis abundant (LEA) proteins or cytoplasmic abundant heat soluble (CAHS) proteins. Despite knowing that IDPs play important roles and are co-enriched alongside endogenous, species-specific cosolutes during desiccation, little is known mechanistically about how IDP-cosolute interactions influence desiccation tolerance. Here, we test the notion that the protective function of desiccation-related IDPs is enhanced through conformational changes induced by endogenous cosolutes. We find that desiccation-related IDPs derived from four different organisms spanning two LEA protein families and the CAHS protein family, synergize best with endogenous cosolutes during drying to promote desiccation protection. Yet the structural parameters of protective IDPs do not correlate with synergy for either CAHS or LEA proteins. We further demonstrate that for CAHS, but not LEA proteins, synergy is related to self-assembly and the formation of a gel. Our results demonstrate that functional synergy between IDPs and endogenous cosolutes is a convergent desiccation protection strategy seen among different IDP families and organisms, yet, the mechanisms underlying this synergy differ between IDP families.

Structural Ensembles of Intrinsically Disordered Proteins Depend Strongly on Force Field

Intrinsically unstructured proteins (IUPs) lack a well defined three-dimensional structure under physiological conditions. They constitute a significant fraction of various proteomes, but only a handful of them have so far been identified. Here we report the development of a two-dimensional electrophoresis technique for their de novo recognition and characterization. This technique consists of the combination of native and 8 m urea electrophoresis of heat-treated proteins where IUPs are expected to run into the diagonal, whereas globular proteins either precipitate upon heat treatment or unfold and run off the diagonal in the second dimension. This behavior was born out by a collection of 10 known IUPs and four globular proteins. By running Escherichia coli and Saccharomyces cerevisiae extracts, several novel IUPs were also identified by mass spectrometric analysis of spots at or near the diagonal. By comparing this novel method to several other techniques, such as the PONDR(R) predictor, hydrophobicity-net charge plot, CD analysis, and gel filtration chromatography, it was shown to provide dependable global assessment of disorder even in dubious cases. Overall the reproducibility and ease of performance of this technique may promote the proteomic scale recognition and characterization of protein disorder.

A set of cross-correlated relaxation experiments to probe the correlation time of two different and complementary spin pairs

Effects of pH on Conformational Equilibria of Intrinsically Disordered Proteins

In this study, we explore the overall structural ensembles and transitions of a biomimetic, multi-stimuli-responsive, intrinsically disordered protein (IDP), Rec1-resilin. The structural transition of Rec1-resilin with change in molecular crowding and environment is evaluated using small-angle neutron scattering and small-angle X-ray scattering. The quantitative analyses of the experimental scattering data using a combination of computational models allowed comprehensive description of the structural evolution, organization, and conformational ensembles of Rec1-resilin in response to the changes in concentration, pH, and temperature. Rec1-resilin in uncrowded solutions demonstrates the equilibrium intrinsic structure quality of an IDP with radius of gyration Rg ∼ 5 nm, and a scattering function for the triaxial ellipsoidal model best fit the experimental dataset. On crowding (increase in concentration >10 wt %), Rec1-resilin molecules exert intermolecular repulsive force of interaction, the Rg value reduces with a progressive increase in concentration, and molecular chains transform from a Gaussian coil to a fully swollen coil. It is also revealed that the structural organization of Rec1-resilin dynamically transforms from a rod (pH 2) to coil (pH 4.8) and to globular (pH 12) as a function of pH. The findings further support the temperature-triggered dual-phase-transition behavior of Rec1-resilin, exhibiting rod-shaped structural organization below the upper critical solution temperature (∼4 °C) and a large but compact structure above the lower critical solution temperature (∼75 °C). This work attempted to correlate unusual responsiveness of Rec1-resilin to the evolution of conformational ensembles.

The heart adapts to cardiac demand via chemical modifications of contractile myofilament proteins. Many of these modifications, such as phosphorylation, occur in proteins' intrinsically disordered regions (IDRs). These IDRs, though challenging to study, are recognized as dynamic, tunable regulators of protein function. Since cardiac dysfunction often involves altered posttranslational modifications (PTMs) in myofilament proteins, understanding how IDR changes affect protein and myofilament behavior is crucial. We hypothesized that PTMs, primarily phosphorylation, regulate ABLIM1 (a myofilament protein) by altering its IDR conformational ensemble, thereby modulating its binding to other myofilament proteins. We tested this using multiscale modeling (including molecular dynamics simulations) to predict ABLIM1's conformational ensembles pre- and postphosphorylation at sites altered in a canine model of heart failure with reduced GSK3β activity. A state-based contraction model then rationalized the physiological consequences. Our data show that local physicochemical alterations from phosphorylation in ABLIM1's IDRs significantly affect its conformational ensemble. This ensemble change subsequently influences the ability of its LIM domains to interact with titin. Furthermore, using the contraction model, we show that a reduced ability to recruit myosin heads for cross-bridge formation, resulting from the modified LIM domain/titin interactions, provides a mechanism that elucidates previous findings of diminished length-dependent activation. These findings offer critical molecular insights, reframing IDRs not merely as structural noise but as key, tunable elements that control protein interactions and ultimately impact mechanical behavior in the sarcomere. This work bridges molecular disorder and biomechanical function, providing a new perspective to understand dynamic control and dysfunction in cardiomyocyte contraction.

Photo-induced electron transfer between tryptophan and cysteine: Temperature dependence.

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTPathological Unfoldomics of Uncontrolled Chaos: Intrinsically Disordered Proteins and Human DiseasesVladimir N. Uversky*†‡§, Vrushank Davé∥⊥, Lilia M. Iakoucheva#, Prerna Malaney∥, Steven J. Metallo▽, Ravi Ramesh Pathak∥, and Andreas C. Joerger*▲View Author Information∥ †Department of Molecular Medicine and USF Health Byrd Alzheimer's Research Institute and ∥Department of Pathology and Cell Biology, Morsani College of Medicine, University of South Florida, Tampa, Florida 33612, United States‡ Institute for Biological Instrumentation, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia§ Department of Biological Sciences, Faculty of Science, King Abdulaziz University, Jeddah 22254, Saudi Arabia⊥ Department of Molecular Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, United States# Department of Psychiatry, University of California San Diego, La Jolla, California 92093, United States▽ Department of Chemistry, Georgetown University, Washington, District of Columbia 20057, United States▲ Medical Research Council Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom*Phone 1-813-974-5816; fax 1-813-974-7357; e-mail [email protected]*Phone +44-1223-267290; e-mail [email protected]Cite this: Chem. Rev. 2014, 114, 13, 6844–6879Publication Date (Web):May 15, 2014Publication History Received15 December 2013Published online15 May 2014Published inissue 9 July 2014https://pubs.acs.org/doi/10.1021/cr400713rhttps://doi.org/10.1021/cr400713rreview-articleACS PublicationsCopyright © 2014 American Chemical SocietyRequest reuse permissionsArticle Views3882Altmetric-Citations215LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Cancer,Diseases and disorders,Genetics,Peptides and proteins,Post-translational modification Get e-Alerts

Intrinsically disordered proteins (IDPs) are highly dynamic systems that play an important role in cell signaling processes and their misfunction often causes human disease. Proper understanding of IDP function not only requires the realistic characterization of their three-dimensional conformational ensembles at atomic-level resolution but also of the time scales of interconversion between their conformational substates. Large sets of experimental data are often used in combination with molecular modeling to restrain or bias models to improve agreement with experiment. It is shown here for the N-terminal transactivation domain of p53 (p53TAD) and Pup, which are two IDPs that fold upon binding to their targets, how the latest advancements in molecular dynamics (MD) simulations methodology produces native conformational ensembles by combining replica exchange with series of microsecond MD simulations. They closely reproduce experimental data at the global conformational ensemble level, in terms of the distribution properties of the radius of gyration tensor, and at the local level, in terms of NMR properties including 15N spin relaxation, without the need for reweighting. Further inspection revealed that 10–20% of the individual MD trajectories display the formation of secondary structures not observed in the experimental NMR data. The IDP ensembles were analyzed by graph theory to identify dominant inter-residue contact clusters and characteristic amino-acid contact propensities. These findings indicate that modern MD force fields with residue-specific backbone potentials can produce highly realistic IDP ensembles sampling a hierarchy of nano- and picosecond time scales providing new insights into their biological function.

Towards the physical basis of how intrinsic disorder mediates protein function

The goal of pE-DB (http://pedb.vib.be) is to serve as an openly accessible database for the deposition of structural ensembles of intrinsically disordered proteins (IDPs) and of denatured proteins based on nuclear magnetic resonance spectroscopy, small-angle X-ray scattering and other data measured in solution. Owing to the inherent flexibility of IDPs, solution techniques are particularly appropriate for characterizing their biophysical properties, and structural ensembles in agreement with these data provide a convenient tool for describing the underlying conformational sampling. Database entries consist of (i) primary experimental data with descriptions of the acquisition methods and algorithms used for the ensemble calculations, and (ii) the structural ensembles consistent with these data, provided as a set of models in a Protein Data Bank format. PE-DB is open for submissions from the community, and is intended as a forum for disseminating the structural ensembles and the methodologies used to generate them. While the need to represent the IDP structures is clear, methods for determining and evaluating the structural ensembles are still evolving. The availability of the pE-DB database is expected to promote the development of new modeling methods and leads to a better understanding of how function arises from disordered states.