1
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Coste A, Slejko E, Zavadlav J, Praprotnik M. Developing an Implicit Solvation Machine Learning Model for Molecular Simulations of Ionic Media. J Chem Theory Comput 2024; 20:411-420. [PMID: 38118122 PMCID: PMC10782447 DOI: 10.1021/acs.jctc.3c00984] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Revised: 12/04/2023] [Accepted: 12/04/2023] [Indexed: 12/22/2023]
Abstract
Molecular dynamics (MD) simulations of biophysical systems require accurate modeling of their native environment, i.e., aqueous ionic solution, as it critically impacts the structure and function of biomolecules. On the other hand, the models should be computationally efficient to enable simulations of large spatiotemporal scales. Here, we present the deep implicit solvation model for sodium chloride solutions that satisfies both requirements. Owing to the use of the neural network potential, the model can capture the many-body potential of mean force, while the implicit water treatment renders the model inexpensive. We demonstrate our approach first for pure ionic solutions with concentrations ranging from physiological to 2 M. We then extend the model to capture the effective ion interactions in the vicinity and far away from a DNA molecule. In both cases, the structural properties are in good agreement with all-atom MD, showcasing a general methodology for the efficient and accurate modeling of ionic media.
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Affiliation(s)
- Amaury Coste
- Laboratory
for Molecular Modeling, National Institute of Chemistry, Ljubljana SI-1001, Slovenia
| | - Ema Slejko
- Laboratory
for Molecular Modeling, National Institute of Chemistry, Ljubljana SI-1001, Slovenia
- Department
of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana SI-1000, Slovenia
| | - Julija Zavadlav
- Professorship
of Multiscale Modeling of Fluid Materials, TUM School of Engineering
and Design, Technical University of Munich, Garching Near Munich DE-85748, Germany
| | - Matej Praprotnik
- Laboratory
for Molecular Modeling, National Institute of Chemistry, Ljubljana SI-1001, Slovenia
- Department
of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana SI-1000, Slovenia
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2
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Knab E, Davis CM. Chemical interactions modulate λ 6-85 stability in cells. Protein Sci 2023; 32:e4698. [PMID: 37313657 PMCID: PMC10288553 DOI: 10.1002/pro.4698] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 05/26/2023] [Accepted: 06/06/2023] [Indexed: 06/15/2023]
Abstract
Because steric crowding is most effective when the crowding agent is similar in size to the molecule that it acts upon and the average macromolecule inside cells is much larger than a small protein or peptide, steric crowding is not predicted to affect their folding inside cells. On the other hand, chemical interactions should perturb in-cell structure and stability because they arise from interactions between the surface of the small protein or peptide and its environment. Indeed, previous in vitro measurements of the λ-repressor fragment, λ6-85 , in crowding matrices comprised of Ficoll or protein crowders support these predictions. Here, we directly quantify the in-cell stability of λ6-85 and distinguish the contribution of steric crowding and chemical interactions to its stability. Using a FRET-labeled λ6-85 construct, we find that the fragment is stabilized by 5°C in-cells compared to in vitro. We demonstrate that this stabilization cannot be explained by steric crowding because, as anticipated, Ficoll has no effect on λ6-85 stability. We find that the in-cell stabilization arises from chemical interactions, mimicked in vitro by mammalian protein extraction reagent (M-PER™). Comparison between FRET values in-cell and in Ficoll confirms that U-2 OS cytosolic crowding is reproduced at macromolecule concentrations of 15% w/v. Our measurements validate the cytomimetic of 15% Ficoll and 20% M-PER™ that we previously developed for protein and RNA folding studies. However, because the in-cell stability of λ6-85 is reproduced by 20% v/v M-PER™ alone, we predict that this simplified mixture could be a useful tool to predict the in-cell behaviors of other small proteins and peptides.
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Affiliation(s)
- Edward Knab
- Department of ChemistryYale UniversityNew HavenConnecticutUSA
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3
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Tripathi P, Firouzbakht A, Gruebele M, Wanunu M. Direct Observation of Single-Protein Transition State Passage by Nanopore Ionic Current Jumps. J Phys Chem Lett 2022; 13:5918-5924. [PMID: 35731125 DOI: 10.1021/acs.jpclett.2c01009] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Conformational transitions of proteins are governed by chemical kinetics, often toggled by passage through an activated state separating two conformational ensembles. The passage time of a protein through the activated state can be too fast to be detected by single-molecule experiments without the aid of viscogenic agents. Here, we use high-bandwidth nanopore measurements to resolve microsecond-duration transitions that occur between conformational states of individual protein molecules partly blocking pore current. We measure the transition state passage time between folded and unfolded states of a two-state λ6-85 mutant and between metastable intermediates and the unfolded state of the multistate folder cytochrome c. Consistent with the principle of microscopic reversibility, the transition state passage time is the same for the forward and backward reactions. A passage time distribution whose tail is broader than a single exponential observed in cytochrome c suggests a multidimensional energy landscape for this protein.
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Affiliation(s)
- Prabhat Tripathi
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, United States
| | | | | | - Meni Wanunu
- Department of Physics, Northeastern University, Boston, Massachusetts 02115, United States
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4
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Grünbein ML, Gorel A, Foucar L, Carbajo S, Colocho W, Gilevich S, Hartmann E, Hilpert M, Hunter M, Kloos M, Koglin JE, Lane TJ, Lewandowski J, Lutman A, Nass K, Nass Kovacs G, Roome CM, Sheppard J, Shoeman RL, Stricker M, van Driel T, Vetter S, Doak RB, Boutet S, Aquila A, Decker FJ, Barends TRM, Stan CA, Schlichting I. Effect of X-ray free-electron laser-induced shockwaves on haemoglobin microcrystals delivered in a liquid jet. Nat Commun 2021; 12:1672. [PMID: 33723266 PMCID: PMC7960726 DOI: 10.1038/s41467-021-21819-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Accepted: 02/15/2021] [Indexed: 01/31/2023] Open
Abstract
X-ray free-electron lasers (XFELs) enable obtaining novel insights in structural biology. The recently available MHz repetition rate XFELs allow full data sets to be collected in shorter time and can also decrease sample consumption. However, the microsecond spacing of MHz XFEL pulses raises new challenges, including possible sample damage induced by shock waves that are launched by preceding pulses in the sample-carrying jet. We explored this matter with an X-ray-pump/X-ray-probe experiment employing haemoglobin microcrystals transported via a liquid jet into the XFEL beam. Diffraction data were collected using a shock-wave-free single-pulse scheme as well as the dual-pulse pump-probe scheme. The latter, relative to the former, reveals significant degradation of crystal hit rate, diffraction resolution and data quality. Crystal structures extracted from the two data sets also differ. Since our pump-probe attributes were chosen to emulate EuXFEL operation at its 4.5 MHz maximum pulse rate, this prompts concern about such data collection.
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Affiliation(s)
- Marie Luise Grünbein
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - Alexander Gorel
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - Lutz Foucar
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - Sergio Carbajo
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - William Colocho
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Sasha Gilevich
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Elisabeth Hartmann
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - Mario Hilpert
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - Mark Hunter
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Marco Kloos
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany ,grid.434729.f0000 0004 0590 2900Present Address: European XFEL GmbH, Schenefeld, Germany
| | - Jason E. Koglin
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA ,grid.148313.c0000 0004 0428 3079Present Address: Los Alamos National Laboratory, Los Alamos, NM USA
| | - Thomas J. Lane
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA ,grid.466493.a0000 0004 0390 1787Present Address: Center for Free-Electron Laser Science, DESY, Hamburg, Germany
| | - Jim Lewandowski
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Alberto Lutman
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Karol Nass
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany ,grid.5991.40000 0001 1090 7501Present Address: Paul Scherrer Institut, Villigen, Switzerland
| | - Gabriela Nass Kovacs
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - Christopher M. Roome
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - John Sheppard
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Robert L. Shoeman
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - Miriam Stricker
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany ,grid.4991.50000 0004 1936 8948Present Address: Department of Statistics, University of Oxford, Oxford, UK
| | - Tim van Driel
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Sharon Vetter
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - R. Bruce Doak
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - Sébastien Boutet
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Andrew Aquila
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Franz Josef Decker
- grid.445003.60000 0001 0725 7771SLAC National Accelerator Laboratory, Menlo Park, CA USA
| | - Thomas R. M. Barends
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
| | - Claudiu Andrei Stan
- grid.430387.b0000 0004 1936 8796Department of Physics, Rutgers University Newark, Newark, NJ USA
| | - Ilme Schlichting
- grid.414703.50000 0001 2202 0959Max Planck Institute for Medical Research, Jahnstrasse 29, Heidelberg, Germany
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5
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Xu X, Gagné D, Aramini JM, Gardner KH. Volume and compressibility differences between protein conformations revealed by high-pressure NMR. Biophys J 2021; 120:924-935. [PMID: 33524371 DOI: 10.1016/j.bpj.2020.12.034] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Revised: 11/25/2020] [Accepted: 12/21/2020] [Indexed: 12/12/2022] Open
Abstract
Proteins often interconvert between different conformations in ways critical to their function. Although manipulating such equilibria for biophysical study is often challenging, the application of pressure is a potential route to achieve such control by favoring the population of lower volume states. Here, we use this feature to study the interconversion of ARNT PAS-B Y456T, which undergoes a dramatic +3 slip in the β-strand register as it switches between two stably folded conformations. Using high-pressure biomolecular NMR approaches, we obtained the first, to our knowledge, quantitative data testing two key hypotheses of this process: the slipped conformation is both smaller and less compressible than the wild-type equivalent, and the interconversion proceeds through a chiefly unfolded intermediate state. Data collected in steady-state pressure and time-resolved pressure-jump modes, including observed pressure-dependent changes in the populations of the two conformers and increased rate of interconversion between conformers, support both hypotheses. Our work exemplifies how these approaches, which can be generally applied to protein conformational switches, can provide unique information that is not easily accessible through other techniques.
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Affiliation(s)
- Xingjian Xu
- Structural Biology Initiative, CUNY Advanced Science Research Center, New York, New York; Ph.D Program in Biochemistry, The Graduate Center, CUNY, New York, New York
| | - Donald Gagné
- Structural Biology Initiative, CUNY Advanced Science Research Center, New York, New York
| | - James M Aramini
- Structural Biology Initiative, CUNY Advanced Science Research Center, New York, New York
| | - Kevin H Gardner
- Structural Biology Initiative, CUNY Advanced Science Research Center, New York, New York; Department of Chemistry and Biochemistry, City College of New York, New York, New York; Ph.D. Programs in Biochemistry, Chemistry, and Biology, The Graduate Center, CUNY, New York, New York.
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6
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The conformational stability of terminal helices of λ-repressor protein in aqueous dodine and choline-O-sulfate solutions. Int J Biol Macromol 2020; 154:1332-1346. [DOI: 10.1016/j.ijbiomac.2019.11.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 10/31/2019] [Accepted: 11/04/2019] [Indexed: 12/18/2022]
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7
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Gasic AG, Cheung MS. A Tale of Two Desolvation Potentials: An Investigation of Protein Behavior under High Hydrostatic Pressure. J Phys Chem B 2020; 124:1619-1627. [DOI: 10.1021/acs.jpcb.9b10734] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Andrei G. Gasic
- Department of Physics, University of Houston, Houston, Texas 77204, United States
- Center for Theoretical Biological Physics, Rice University, Houston, Texas 77005, United States
| | - Margaret S. Cheung
- Department of Physics, University of Houston, Houston, Texas 77204, United States
- Center for Theoretical Biological Physics, Rice University, Houston, Texas 77005, United States
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8
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Liu C, Li Y, Liu BF. Micromixers and their applications in kinetic analysis of biochemical reactions. Talanta 2019; 205:120136. [DOI: 10.1016/j.talanta.2019.120136] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 07/03/2019] [Accepted: 07/08/2019] [Indexed: 01/11/2023]
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9
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Fast pressure-jump all-atom simulations and experiments reveal site-specific protein dehydration-folding dynamics. Proc Natl Acad Sci U S A 2019; 116:5356-5361. [PMID: 30837309 DOI: 10.1073/pnas.1814927116] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
As theory and experiment have shown, protein dehydration is a major contributor to protein folding. Dehydration upon folding can be characterized directly by all-atom simulations of fast pressure drops, which create desolvated pockets inside the nascent hydrophobic core. Here, we study pressure-drop refolding of three λ-repressor fragment (λ6-85) mutants computationally and experimentally. The three mutants report on tertiary structure formation via different fluorescent helix-helix contact pairs. All-atom simulations of pressure drops capture refolding and unfolding of all three mutants by a similar mechanism, thus validating the nonperturbative nature of the fluorescent contact probes. Analysis of simulated interprobe distances shows that the α-helix 1-3 pair distance displays a slower characteristic time scale than the 1-2 or 3-2 pair distance. To see whether slow packing of α-helices 1 and 3 is reflected in the rate-limiting folding step, fast pressure-drop relaxation experiments captured refolding on a millisecond time scale. These experiments reveal that refolding monitored by 1-3 contact formation indeed is much slower than when monitored by 1-2 or 3-2 contact formation. Unlike the case of the two-state folder [three-α-helix bundle (α3D)], whose drying and core formation proceed in concert, λ6-85 repeatedly dries and rewets different local tertiary contacts before finally forming a solvent-excluded core, explaining the non-two-state behavior observed during refolding in molecular dynamics simulations. This work demonstrates that proteins can explore desolvated pockets and dry globular states numerous times before reaching the native conformation.
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10
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Schneider S, Paulsen H, Reiter KC, Hinze E, Schiene-Fischer C, Hübner CG. Single molecule FRET investigation of pressure-driven unfolding of cold shock protein A. J Chem Phys 2018; 148:123336. [DOI: 10.1063/1.5009662] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Affiliation(s)
- Sven Schneider
- Institute of Physics, University of Lübeck, Lübeck D-23562, Germany
| | - Hauke Paulsen
- Institute of Physics, University of Lübeck, Lübeck D-23562, Germany
| | - Kim Colin Reiter
- Institute of Physics, University of Lübeck, Lübeck D-23562, Germany
| | - Erik Hinze
- Max Planck Research Unit for Enzymology of Protein Folding Halle, Halle/Saale D-06120, Germany
| | - Cordelia Schiene-Fischer
- Department of Enzymology, Institute for Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, Halle/Saale D-06120, Germany
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11
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Alderson TR, Charlier C, Torchia DA, Anfinrud P, Bax A. Monitoring Hydrogen Exchange During Protein Folding by Fast Pressure Jump NMR Spectroscopy. J Am Chem Soc 2017; 139:11036-11039. [PMID: 28766333 DOI: 10.1021/jacs.7b06676] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A method is introduced that permits direct observation of the rates at which backbone amide hydrogens become protected from solvent exchange after rapidly dropping the hydrostatic pressure inside the NMR sample cell from denaturing (2.5 kbar) to native (1 bar) conditions. The method is demonstrated for a pressure-sensitized ubiquitin variant that contains two Val to Ala mutations. Increased protection against hydrogen exchange with solvent is monitored as a function of time during the folding process. Results for 53 backbone amides show narrow clustering with protection occurring with a time constant of ca. 85 ms, but slower protection is observed around a reverse turn near the C-terminus of the protein. Remarkably, the native NMR spectrum returns with this slower time constant of ca. 150 ms, indicating that the almost fully folded protein retains molten globule characteristics with severe NMR line broadening until the final hydrogen bonds are formed. Prior to crossing the transition state barrier, hydrogen exchange protection factors are close to unity, but with slightly elevated values in the β1-β2 hairpin, previously shown to be already lowly populated in the urea-denatured state.
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Affiliation(s)
- T Reid Alderson
- Laboratory of Chemical Physics, NIDDK, National Institutes of Health , Bethesda, Maryland 20892-0520, United States
| | - Cyril Charlier
- Laboratory of Chemical Physics, NIDDK, National Institutes of Health , Bethesda, Maryland 20892-0520, United States
| | - Dennis A Torchia
- Laboratory of Chemical Physics, NIDDK, National Institutes of Health , Bethesda, Maryland 20892-0520, United States
| | - Philip Anfinrud
- Laboratory of Chemical Physics, NIDDK, National Institutes of Health , Bethesda, Maryland 20892-0520, United States
| | - Ad Bax
- Laboratory of Chemical Physics, NIDDK, National Institutes of Health , Bethesda, Maryland 20892-0520, United States
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12
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Best RB, Miller C, Mittal J. Role of solvation in pressure-induced helix stabilization. J Chem Phys 2015; 141:22D522. [PMID: 25494793 DOI: 10.1063/1.4901112] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In contrast to the well-known destabilization of globular proteins by high pressure, recent work has shown that pressure stabilizes the formation of isolated α-helices. However, all simulations to date have obtained a qualitatively opposite result within the experimental pressure range. We show that using a protein force field (Amber03w) parametrized in conjunction with an accurate water model (TIP4P/2005) recovers the correct pressure-dependence and an overall stability diagram for helix formation similar to that from experiment; on the other hand, we confirm that using TIP3P water results in a very weak pressure destabilization of helices. By carefully analyzing the contributing factors, we show that this is not merely a consequence of different peptide conformations sampled using TIP3P. Rather, there is a critical role for the solvent itself in determining the dependence of total system volume (peptide and solvent) on helix content. Helical peptide structures exclude a smaller volume to water, relative to non-helical structures with both the water models, but the total system volume for helical conformations is higher than non-helical conformations with TIP3P water at low to intermediate pressures, in contrast to TIP4P/2005 water. Our results further emphasize the importance of using an accurate water model to study protein folding under conditions away from standard temperature and pressure.
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Affiliation(s)
- Robert B Best
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0520, USA
| | - Cayla Miller
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, Pennsylvania 18015, USA
| | - Jeetain Mittal
- Department of Chemical and Biomolecular Engineering, Lehigh University, Bethlehem, Pennsylvania 18015, USA
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13
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Sirovetz BJ, Schafer NP, Wolynes PG. Water Mediated Interactions and the Protein Folding Phase Diagram in the Temperature–Pressure Plane. J Phys Chem B 2015; 119:11416-27. [DOI: 10.1021/acs.jpcb.5b03828] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Brian J. Sirovetz
- Center
for Theoretical Biological Physics, Rice University, 6500 Main
Street, Houston, Texas 77030, United States
- Department
of Chemistry, Rice University, Space Science 201, Houston, Texas 77251, United States
| | - Nicholas P. Schafer
- Center
for Theoretical Biological Physics, Rice University, 6500 Main
Street, Houston, Texas 77030, United States
| | - Peter G. Wolynes
- Center
for Theoretical Biological Physics, Rice University, 6500 Main
Street, Houston, Texas 77030, United States
- Department
of Chemistry, Rice University, Space Science 201, Houston, Texas 77251, United States
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14
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Abstract
Fast protein folding involves complex dynamics in many degrees of freedom, yet microsecond folding experiments provide only low-resolution structural information. We enhance the structural resolution of the five-helix bundle protein λ6-85 by engineering into it three fluorescent tryptophan-tyrosine contact probes. The probes report on distances between three different helix pairs: 1-2, 1-3, and 3-2. Temperature jump relaxation experiments on these three mutants reveal two different kinetic timescales: a slower timescale for 1-3 and a faster one for the two contacts involving helix 2. We hypothesize that these differences arise from a single folding mechanism that forms contacts on different timescales, and not from changes of mechanism due to adding the probes. To test this hypothesis, we analyzed the corresponding three distances in one published single-trajectory all-atom molecular-dynamics simulation of a similar mutant. Autocorrelation analysis of the trajectory reveals the same "slow" and "fast" distance change as does experiment, but on a faster timescale; smoothing the trajectory in time shows that this ordering is robust and persists into the microsecond folding timescale. Structural investigation of the all-atom computational data suggests that helix 2 misfolds to produce a short-lived off-pathway trap, in agreement with the experimental finding that the 1-2 and 3-2 distances involving helix 2 contacts form a kinetic grouping distinct from 1 to 3. Our work demonstrates that comparison between experiment and simulation can be extended to several order parameters, providing a stronger mechanistic test.
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15
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Wirth AJ, Liu Y, Prigozhin MB, Schulten K, Gruebele M. Comparing Fast Pressure Jump and Temperature Jump Protein Folding Experiments and Simulations. J Am Chem Soc 2015; 137:7152-7159. [PMID: 25988868 DOI: 10.1021/jacs.5b02474] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The unimolecular folding reaction of small proteins is now amenable to a very direct mechanistic comparison between experiment and simulation. We present such a comparison of microsecond pressure and temperature jump refolding kinetics of the engineered WW domain FiP35, a model system for β-sheet folding. Both perturbations produce experimentally a faster and a slower kinetic phase, and the "slow" microsecond phase is activated. The fast phase shows differences between perturbation methods and is closer to the downhill limit by temperature jump, but closer to the transiently populated intermediate limit by pressure jump. These observations make more demands on simulations of the folding process than just a rough comparison of time scales. To complement experiments, we carried out several pressure jump and temperature jump all-atom molecular dynamics trajectories in explicit solvent, where FiP35 folded in five of the six simulations. We analyzed our pressure jump simulations by kinetic modeling and found that the pressure jump experiments and MD simulations are most consistent with a 4-state kinetic mechanism. Together, our experimental and computational data highlight FiP35's position at the boundary where activated intermediates and downhill folding meet, and we show that this model protein is an excellent candidate for further pressure jump molecular dynamics studies to compare experiment and modeling at the folding mechanism level.
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Affiliation(s)
- Anna Jean Wirth
- Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States
| | - Yanxin Liu
- Department of Physics, and Beckman Institute, University of Illinois, Urbana, Illinois 61801, United States
| | - Maxim B Prigozhin
- Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States
| | - Klaus Schulten
- Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States.,Center for Biophysics and Computational Biology, University of Illinois, Urbana, Illinois 61801, United States.,Department of Physics, and Beckman Institute, University of Illinois, Urbana, Illinois 61801, United States
| | - Martin Gruebele
- Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States.,Center for Biophysics and Computational Biology, University of Illinois, Urbana, Illinois 61801, United States.,Department of Physics, and Beckman Institute, University of Illinois, Urbana, Illinois 61801, United States
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16
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A hypothesis to reconcile the physical and chemical unfolding of proteins. Proc Natl Acad Sci U S A 2015; 112:E2775-84. [PMID: 25964355 DOI: 10.1073/pnas.1500352112] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
High pressure (HP) or urea is commonly used to disturb folding species. Pressure favors the reversible unfolding of proteins by causing changes in the volumetric properties of the protein-solvent system. However, no mechanistic model has fully elucidated the effects of urea on structure unfolding, even though protein-urea interactions are considered to be crucial. Here, we provide NMR spectroscopy and 3D reconstructions from X-ray scattering to develop the "push-and-pull" hypothesis, which helps to explain the initial mechanism of chemical unfolding in light of the physical events triggered by HP. In studying MpNep2 from Moniliophthora perniciosa, we tracked two cooperative units using HP-NMR as MpNep2 moved uphill in the energy landscape; this process contrasts with the overall structural unfolding that occurs upon reaching a threshold concentration of urea. At subdenaturing concentrations of urea, we were able to trap a state in which urea is preferentially bound to the protein (as determined by NMR intensities and chemical shifts); this state is still folded and not additionally exposed to solvent [fluorescence and small-angle X-ray scattering (SAXS)]. This state has a higher susceptibility to pressure denaturation (lower p1/2 and larger ΔVu); thus, urea and HP share concomitant effects of urea binding and pulling and water-inducing pushing, respectively. These observations explain the differences between the molecular mechanisms that control the physical and chemical unfolding of proteins, thus opening up new possibilities for the study of protein folding and providing an interpretation of the nature of cooperativity in the folding and unfolding processes.
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