1
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Somarathne RP, Amarasekara DL, Kariyawasam CS, Robertson HA, Mayatt R, Gwaltney SR, Fitzkee NC. Protein Binding Leads to Reduced Stability and Solvated Disorder in the Polystyrene Nanoparticle Corona. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2024; 20:e2305684. [PMID: 38247186 PMCID: PMC11209821 DOI: 10.1002/smll.202305684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 01/03/2024] [Indexed: 01/23/2024]
Abstract
Understanding the conformation of proteins in the nanoparticle corona has important implications in how organisms respond to nanoparticle-based drugs. These proteins coat the nanoparticle surface, and their properties will influence the nanoparticle's interaction with cell targets and the immune system. While some coronas are thought to be disordered, two key unanswered questions are the degree of disorder and solvent accessibility. Here, a model is developed for protein corona disorder in polystyrene nanoparticles of varying size. For two different proteins, it is found that binding affinity decreases as nanoparticle size increases. The stoichiometry of binding, along with changes in the hydrodynamic size, supports a highly solvated, disordered protein corona anchored at a small number of attachment sites. The scaling of the stoichiometry versus nanoparticle size is consistent with disordered polymer dimensions. Moreover, it is found that proteins are destabilized less in the presence of larger nanoparticles, and hydrophobic exposure decreases at lower curvatures. The observations hold for proteins on flat polystyrene surfaces, which have the lowest hydrophobic exposure. The model provides an explanation for previous observations of increased amyloid fibrillation rates in the presence of larger nanoparticles, and it may rationalize how cell receptors can recognize protein disorder in therapeutic nanoparticles.
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Affiliation(s)
- Radha P Somarathne
- Department of Chemistry, Mississippi State University, Mississippi State, MS, 39762, USA
| | - Dhanush L Amarasekara
- Department of Chemistry, Mississippi State University, Mississippi State, MS, 39762, USA
| | - Chathuri S Kariyawasam
- Department of Chemistry, Mississippi State University, Mississippi State, MS, 39762, USA
| | - Harley A Robertson
- Department of Chemistry, Mississippi State University, Mississippi State, MS, 39762, USA
| | - Railey Mayatt
- Department of Chemistry, Mississippi State University, Mississippi State, MS, 39762, USA
| | - Steven R Gwaltney
- Department of Chemistry, Mississippi State University, Mississippi State, MS, 39762, USA
| | - Nicholas C Fitzkee
- Department of Chemistry, Mississippi State University, Mississippi State, MS, 39762, USA
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2
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Chang L, Perez A. Deciphering the Folding Mechanism of Proteins G and L and Their Mutants. J Am Chem Soc 2022; 144:14668-14677. [PMID: 35930769 DOI: 10.1021/jacs.2c04488] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Much of our understanding of folding mechanisms comes from interpretations of experimental ϕ and ψ value analysis, relating the differences in stability of the transition state ensemble (TSE) and folded state. We introduce a unified approach combining simulations and Bayesian inference to provide atomistic detail for the folding mechanism of proteins G and L and their mutants. Proteins G and L fold to similar topologies despite low sequence similarity, but differ in their folding pathways. A fast folding redesign of protein G, NuG2, switches folding pathways and folds through a similar pathway with protein L. A redesign of protein L also leads to faster folding, respecting the original folding pathway. Our Bayesian inference approach starts from the same prior on all systems and correctly identifies the folding mechanism for each of the four proteins, a success of the force field and sampling strategy. The approach is computationally efficient and correctly identifies the TSE and intermediate structures along the folding pathway in good agreement with experiments. We complement our findings by using two orthogonal approaches that differ in computational cost and interpretability. Adaptive sampling MD combined with the Markov state model provides a kinetic model that confirms the more complex folding mechanism of protein G and its mutant. Finally, a novel fragment decomposition approach using AlphaFold identifies preferences for secondary structure element combinations that follow the order of events observed in the folding pathways.
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Affiliation(s)
- Liwei Chang
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States.,Quantum Theory Project, University of Florida, Gainesville, Florida 32611, United States
| | - Alberto Perez
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States.,Quantum Theory Project, University of Florida, Gainesville, Florida 32611, United States
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3
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Mizukami T, Bedford JT, Liao S, Greene LH, Roder H. Effects of ionic strength on the folding and stability of SAMP1, a ubiquitin-like halophilic protein. Biophys J 2022; 121:552-564. [PMID: 35063455 PMCID: PMC8874027 DOI: 10.1016/j.bpj.2022.01.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 12/13/2021] [Accepted: 01/13/2022] [Indexed: 11/21/2022] Open
Abstract
Our knowledge of the folding behavior of proteins from extremophiles is limited at this time. These proteins may more closely resemble the primordial proteins selected in early evolution under extreme conditions. The small archaeal modifier protein 1 (SAMP1) studied in this report is an 87-residue protein with a β-grasp fold found in the halophile Haloferax volcanii from the Dead Sea. To gain insight into the effects of salt on the stability and folding mechanism of SAMP1, we conducted equilibrium and kinetic folding experiments as a function of sodium chloride concentration. The results revealed that increasing ionic strength accelerates refolding and slows down unfolding of SAMP1, giving rise to a pronounced salt-induced stabilization. With increasing NaCl concentration, the rate of folding observed via a combination of continuous-flow (0.1-2 ms time range) and stopped-flow measurements (>2 ms) exhibited a >100-fold increase between 0.1 and 1.5 M NaCl and leveled off at higher concentrations. Using the Linderström-Lang smeared charge formalism to model electrostatic interactions in ground and transition states encountered during folding, we showed that the observed salt dependence is dominated by Debye-Hückel screening of electrostatic repulsion among numerous negatively charged residues. Comparisons are also drawn with three well-studied mesophilic members of the β-grasp superfamily: protein G, protein L, and ubiquitin. Interestingly, the folding rate of SAMP1 in 3 M sodium chloride is comparable to that of protein G, ubiquitin, and protein L at lower ionic strength. The results indicate the important role of electrostatic interactions in protein folding and imply that proteins have evolved to minimize unfavorable charge-charge interactions under their specific native conditions.
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Affiliation(s)
- Takuya Mizukami
- Molecular Therapeutics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania
| | - John T Bedford
- Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia
| | - ShanHui Liao
- School of Life Sciences, University of Science and Technology of China, Hefei National Laboratory for Physical Sciences at Microscale, School of Life Science, Hefei, Anhui, P.R. China
| | - Lesley H Greene
- Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, Virginia.
| | - Heinrich Roder
- Molecular Therapeutics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania.
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4
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Bedford JT, Poutsma J, Diawara N, Greene LH. The nature of persistent interactions in two model β-grasp proteins reveals the advantage of symmetry in stability. J Comput Chem 2021; 42:600-607. [PMID: 33534913 DOI: 10.1002/jcc.26477] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Revised: 10/27/2020] [Accepted: 11/22/2020] [Indexed: 01/25/2023]
Abstract
Two proteins within the β-grasp superfamily, the B1-domain of protein G and the small archaeal modifier protein 1, were investigated to elucidate the key determinants of structural stability at the level of individual interactions. These symmetrical proteins both contain two β-hairpins which form a sheet flanked by a central α-helix. They were subjected to high temperature molecular dynamics simulations and the detailed behavior of each long-range interaction was characterized. The results revealed that in GB1 the most stable region was the C-terminal hairpin and in SAMP1 it was the opposite, the N-terminal hairpin. Experimental results for GB1 support this finding. In conclusion, it appears that the difference in the location and number of hydrophobic interactions dictate the differential stability which is accommodated due to structural symmetry of the β-grasp fold. Thus, the hairpins are interchangeable and in nature this lends itself to adaptability and flexibility.
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5
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Crilly CJ, Brom JA, Kowalewski ME, Piszkiewicz S, Pielak GJ. Dried Protein Structure Revealed at the Residue Level by Liquid-Observed Vapor Exchange NMR. Biochemistry 2021; 60:152-159. [PMID: 33400518 DOI: 10.1021/acs.biochem.0c00863] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Water is key to protein structure and stability, yet the relationship between protein-water interactions and structure is poorly understood, in part because there are few techniques that permit the study of dehydrated protein structure at high resolution. Here, we describe liquid-observed vapor exchange (LOVE) NMR, a solution NMR-based method that provides residue-level information about the structure of dehydrated proteins. Using the model protein GB1, we show that LOVE NMR measurements reflect the fraction of the dried protein population trapped in a conformation where a given residue is protected from exchange with D2O vapor. Comparisons to solution hydrogen-deuterium exchange data affirm that the dried protein structure is strongly influenced by local solution stability and that the mechanism of dehydration protection exerted by the widely used protectant trehalose differs from its mechanism of stabilization in solution. Our results highlight the need for refined models of cosolute-mediated dehydration protection and demonstrate the ability of LOVE NMR to inform such models.
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Affiliation(s)
- Candice J Crilly
- Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Julia A Brom
- Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Mark E Kowalewski
- Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Samantha Piszkiewicz
- Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States
| | - Gary J Pielak
- Department of Chemistry, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, United States.,Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.,Lineberger Cancer Center, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.,Integrative Program for Biological & Genome Sciences, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7100, United States
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6
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Guo Z, Hong H, Yuan G, Qian H, Li B, Cao Y, Wang W, Wu CX, Chen H. Hidden Intermediate State and Second Pathway Determining Folding and Unfolding Dynamics of GB1 Protein at Low Forces. PHYSICAL REVIEW LETTERS 2020; 125:198101. [PMID: 33216575 DOI: 10.1103/physrevlett.125.198101] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 10/12/2020] [Indexed: 06/11/2023]
Abstract
Atomic force microscopy experiments found that GB1, a typical two-state model protein used for study of folding and unfolding dynamics, can sustain forces of more than 100 pN, but its response to low forces still remains unclear. Using ultrastable magnetic tweezers, we discovered that GB1 has an unexpected nonmonotonic force-dependent unfolding rate at 5-160 pN, from which a free energy landscape with two main barriers and a hidden intermediate state was constructed. A model combining two separate models by Dudko et al. with two pathways between the native state and this intermediate state is proposed to rebuild the unfolding dynamics over the full experimental force range. One candidate of this transient intermediate state is the theoretically proposed molten globule state with a loosely collapsed conformation, which might exist universally in the folding and unfolding processes of two-state proteins.
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Affiliation(s)
- Zilong Guo
- Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Lab for Soft Functional Materials Research, Department of Physics, Xiamen University, Xiamen 361005, China
| | - Haiyan Hong
- Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Lab for Soft Functional Materials Research, Department of Physics, Xiamen University, Xiamen 361005, China
| | - Guohua Yuan
- Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Lab for Soft Functional Materials Research, Department of Physics, Xiamen University, Xiamen 361005, China
| | - Hui Qian
- Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Lab for Soft Functional Materials Research, Department of Physics, Xiamen University, Xiamen 361005, China
| | - Bing Li
- National Laboratory of Solid State Microstructure, Department of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Yi Cao
- National Laboratory of Solid State Microstructure, Department of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Wei Wang
- National Laboratory of Solid State Microstructure, Department of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
| | - Chen-Xu Wu
- Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Lab for Soft Functional Materials Research, Department of Physics, Xiamen University, Xiamen 361005, China
| | - Hu Chen
- Research Institute for Biomimetics and Soft Matter, Fujian Provincial Key Lab for Soft Functional Materials Research, Department of Physics, Xiamen University, Xiamen 361005, China
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7
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Syzonenko I, Phillips JL. Accelerated Protein Folding Using Greedy-Proximal A*. J Chem Inf Model 2020; 60:3093-3104. [DOI: 10.1021/acs.jcim.9b01194] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ivan Syzonenko
- Computational Sciences PhD Program, Middle Tennessee State University, Murfreesboro, Tennessee 37132, United States
- Middle Tennessee State University, Murfreesboro, Tennessee 37132, United States
| | - Joshua L. Phillips
- Department of Computer Science, Middle Tennessee State University, Murfreesboro, Tennessee 37132, United States
- Middle Tennessee State University, Murfreesboro, Tennessee 37132, United States
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8
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Bogetti X, Ghosh S, Gamble Jarvi A, Wang J, Saxena S. Molecular Dynamics Simulations Based on Newly Developed Force Field Parameters for Cu 2+ Spin Labels Provide Insights into Double-Histidine-Based Double Electron-Electron Resonance. J Phys Chem B 2020; 124:2788-2797. [PMID: 32181671 DOI: 10.1021/acs.jpcb.0c00739] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Electron paramagnetic resonance (EPR) in combination with the recently developed double-histidine (dHis)-based Cu2+ spin labeling has provided valuable insights into protein structure and conformational dynamics. To relate sparse distance constraints measured by EPR to protein fluctuations in solution, modeling techniques are needed. In this work, we have developed force field parameters for Cu2+-nitrilotriacetic and Cu2+-iminodiacetic acid spin labels. We employed molecular dynamics (MD) simulations to capture the atomic-level details of dHis-labeled protein fluctuations. The interspin distances extracted from 200 ns MD trajectories show good agreement with the experimental results. The MD simulations also illustrate the dramatic rigidity of the Cu2+ labels compared to the standard nitroxide spin label. Further, the relative orientations between spin-labeled sites were measured to provide insight into the use of double electron-electron resonance (DEER) methods for such labels. The relative mean angles, as well as the standard deviations of the relative angles, agree well in general with the spectral simulations published previously. The fluctuations of relative orientations help rationalize why orientation selectivity effects are minimal at X-band frequencies, but observable at the Q-band for such labels. In summary, the results show that by combining the experimental results with MD simulations precise information about protein conformations as well as flexibility can be obtained.
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Affiliation(s)
- Xiaowei Bogetti
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Shreya Ghosh
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Austin Gamble Jarvi
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Junmei Wang
- Department of Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15206, United States
| | - Sunil Saxena
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
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9
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Becerra D, Butyaev A, Waldispühl J. Fast and flexible coarse-grained prediction of protein folding routes using ensemble modeling and evolutionary sequence variation. Bioinformatics 2020; 36:1420-1428. [PMID: 31584628 DOI: 10.1093/bioinformatics/btz743] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Revised: 09/22/2019] [Accepted: 09/28/2019] [Indexed: 11/15/2022] Open
Abstract
MOTIVATION Protein folding is a dynamic process through which polypeptide chains reach their native 3D structures. Although the importance of this mechanism is widely acknowledged, very few high-throughput computational methods have been developed to study it. RESULTS In this paper, we report a computational platform named P3Fold that combines statistical and evolutionary information for predicting and analyzing protein folding routes. P3Fold uses coarse-grained modeling and efficient combinatorial schemes to predict residue contacts and evaluate the folding routes of a protein sequence within minutes or hours. To facilitate access to this technology, we devise graphical representations and implement an interactive web interface that allows end-users to leverage P3Fold predictions. Finally, we use P3Fold to conduct large and short scale experiments on the human proteome that reveal the broad conservation and variations of structural intermediates within protein families. AVAILABILITY AND IMPLEMENTATION A Web server of P3Fold is freely available at http://csb.cs.mcgill.ca/P3Fold. SUPPLEMENTARY INFORMATION Supplementary data are available at Bioinformatics online.
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Affiliation(s)
- David Becerra
- School of Computer Science, McGill University, Montréal, QC H3A 0E9, Canada
| | - Alexander Butyaev
- School of Computer Science, McGill University, Montréal, QC H3A 0E9, Canada
| | - Jérôme Waldispühl
- School of Computer Science, McGill University, Montréal, QC H3A 0E9, Canada
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10
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Wei S, Zou X, Tian J, Huang H, Guo W, Chen Z. Control of Protein Conformation and Orientation on Graphene. J Am Chem Soc 2019; 141:20335-20343. [PMID: 31774666 DOI: 10.1021/jacs.9b10705] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Graphene-based biosensors have attracted considerable attention due to their advantages of label-free detection and high sensitivity. Many such biosensors utilize noncovalent van der Waals force to attach proteins onto graphene surface while preserving graphene's high conductivity. Maintaining the protein structure without denaturation/substantial conformational change and controlling proper protein orientation on the graphene surface are critical for biosensing applications of these biosensors fabricated with proteins on graphene. Based on the knowledge we obtained from our previous experimental study and computer modeling of amino acid residual level interactions between graphene and peptides, here we systemically redesigned an important protein for better conformational stability and desirable orientation on graphene. In this paper, immunoglobulin G (IgG) antibody-binding domain of protein G (protein GB1) was studied to demonstrate how we can preserve the protein native structure and control the protein orientation on graphene surface by redesigning protein mutants. Various experimental tools including sum frequency generation vibrational spectroscopy, attenuated total refection-Fourier transform infrared spectroscopy, fluorescence spectroscopy, and circular dichroism spectroscopy were used to study the protein GB1 structure on graphene, supplemented by molecular dynamics simulations. By carefully designing the protein GB1 mutant, we can avoid strong unfavorable interactions between protein and graphene to preserve protein conformation and to enable the protein to adopt a preferred orientation. The methodology developed in this study is general and can be applied to study different proteins on graphene and beyond. With the knowledge obtained from this research, one could apply this method to optimize protein function on surfaces (e.g., to enhance biosensor sensitivity).
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Affiliation(s)
- Shuai Wei
- Department of Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Xingquan Zou
- Department of Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Jiayi Tian
- Department of Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Hao Huang
- Department of Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Wen Guo
- Department of Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Zhan Chen
- Department of Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
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11
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Cheng Q, Joung I, Lee J, Kuwajima K, Lee J. Exploring the Folding Mechanism of Small Proteins GB1 and LB1. J Chem Theory Comput 2019; 15:3432-3449. [DOI: 10.1021/acs.jctc.8b01163] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Qianyi Cheng
- Department of Chemistry, University of Memphis, Memphis, Tennessee 38152, United States
- School of Computational Sciences, Korea Institute for Advanced Study, Seoul 02455, South Korea
| | - InSuk Joung
- Department of Chemistry, Kangwon National University, Chuncheon 24341, South Korea
- School of Computational Sciences, Korea Institute for Advanced Study, Seoul 02455, South Korea
| | - Juyong Lee
- Department of Chemistry, Kangwon National University, Chuncheon 24341, South Korea
| | - Kunihiro Kuwajima
- Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
- School of Computational Sciences, Korea Institute for Advanced Study, Seoul 02455, South Korea
| | - Jooyoung Lee
- Center for In Silico Protein Science, Korea Institute for Advanced Study, Seoul 02455, South Korea
- School of Computational Sciences, Korea Institute for Advanced Study, Seoul 02455, South Korea
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12
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Gamble Jarvi A, Ranguelova K, Ghosh S, Weber RT, Saxena S. On the Use of Q-Band Double Electron–Electron Resonance To Resolve the Relative Orientations of Two Double Histidine-Bound Cu2+ Ions in a Protein. J Phys Chem B 2018; 122:10669-10677. [DOI: 10.1021/acs.jpcb.8b07727] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Austin Gamble Jarvi
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Kalina Ranguelova
- Bruker BioSpin, Inc., EPR Division, 15 Fortune Drive, Billerica, Massachusetts 01821, United States
| | - Shreya Ghosh
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
| | - Ralph T. Weber
- Bruker BioSpin, Inc., EPR Division, 15 Fortune Drive, Billerica, Massachusetts 01821, United States
| | - Sunil Saxena
- Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
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13
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Berkovich R, Mondal J, Paster I, Berne BJ. Simulated Force Quench Dynamics Shows GB1 Protein Is Not a Two State Folder. J Phys Chem B 2017; 121:5162-5173. [PMID: 28453938 DOI: 10.1021/acs.jpcb.7b00610] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Single molecule force spectroscopy is a useful technique for investigating mechanically induced protein unfolding and refolding under reduced forces by monitoring the end-to-end distance of the protein. The data is often interpreted via a "two-state" model based on the assumption that the end-to-end distance alone is a good reaction coordinate and the thermodynamic behavior is then ascribed to the free energy as a function of this one reaction coordinate. In this paper, we determined the free energy surface (PMF) of GB1 protein from atomistic simulations in explicit solvent under different applied forces as a function of two collective variables (the end-to-end-distance, and the fraction of native contacts ρ). The calculated 2-d free energy surfaces exhibited several distinct states, or basins, mostly visible along the ρ coordinate. Brownian dynamics (BD) simulations on the smoothed free energy surface show that the protein visits a metastable molten globule state and is thus a three state folder, not the two state folder inferred using the end-to-end distance as the sole reaction coordinate. This study lends support to recent experiments that suggest that GB1 is not a two-state folder.
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Affiliation(s)
- Ronen Berkovich
- Department of Chemical Engineering, Ben-Gurion University of the Negev , Beer-Sheva 84105, Israel
| | - Jagannath Mondal
- Tata Institute of Fundamental Research, Centre for Interdisciplinary Sciences , Hyderabad, India
| | - Inga Paster
- Department of Chemical Engineering, Ben-Gurion University of the Negev , Beer-Sheva 84105, Israel
| | - B J Berne
- Department of Chemistry, Columbia University , New York, New York 10027, United States
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14
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Song C, Wang Q, Xue T, Wang Y, Chen G. Molecular dynamics simulations on the conformational transitions from the G A 98 (G A 88) to G B 98 (G B 88) proteins. J Mol Recognit 2016; 29:580-595. [PMID: 27480925 DOI: 10.1002/jmr.2558] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 06/11/2016] [Accepted: 07/04/2016] [Indexed: 12/19/2022]
Abstract
We performed conventional and targeted molecular dynamics simulations to address the dynamic transition mechanisms of the conformational transitions from the GA 98 protein with only 1 mutation of Leu45Tyr to GB 98 and from the GA 88 protein with 7 mutations of Gly24Ala, Ile25Thr, Ile30Phe, Ile33Tyr, Leu45Tyr, Ile49Thr, and Leu50Lys to GB 88. The results show that the conformational transition mechanism from the mutated 3α GA 98 (GA 88) state to the α+4β GB 98 (GB 88) state via several intermediate conformations involves the bending of loops at the N and C termini firstly, the unfolding of αA and αC, then the traversing of αB, and the formation of the 4β layer with the conversion of the hydrophobic core. The bending of loops at the N and C termini and the formation of the crucial transition conformation with the full unfolded structure are key factors in their transition processes. The communication of the interaction network, the bending directions of loops, and the traversing site of αB in the transition of GA 98 to GB 98 are markedly different from those in GA 88 to GB 88 because of the different mutated residues. The analysis of the correlations and the calculated mass center distances between some segments further supported their conformational transition mechanisms. These results could help people to better understand the Paracelsus challenge. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Chunnian Song
- College of Chemistry, Beijing Normal University, Beijing, China
| | - Qing Wang
- College of Chemistry, Beijing Normal University, Beijing, China
| | - Tuo Xue
- College of Chemistry, Beijing Normal University, Beijing, China
| | - Yan Wang
- College of Chemistry, Beijing Normal University, Beijing, China
| | - Guangju Chen
- College of Chemistry, Beijing Normal University, Beijing, China
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15
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Sikosek T, Krobath H, Chan HS. Theoretical Insights into the Biophysics of Protein Bi-stability and Evolutionary Switches. PLoS Comput Biol 2016; 12:e1004960. [PMID: 27253392 PMCID: PMC4890782 DOI: 10.1371/journal.pcbi.1004960] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Accepted: 05/04/2016] [Indexed: 11/18/2022] Open
Abstract
Deciphering the effects of nonsynonymous mutations on protein structure is central to many areas of biomedical research and is of fundamental importance to the study of molecular evolution. Much of the investigation of protein evolution has focused on mutations that leave a protein’s folded structure essentially unchanged. However, to evolve novel folds of proteins, mutations that lead to large conformational modifications have to be involved. Unraveling the basic biophysics of such mutations is a challenge to theory, especially when only one or two amino acid substitutions cause a large-scale conformational switch. Among the few such mutational switches identified experimentally, the one between the GA all-α and GB α+β folds is extensively characterized; but all-atom simulations using fully transferrable potentials have not been able to account for this striking switching behavior. Here we introduce an explicit-chain model that combines structure-based native biases for multiple alternative structures with a general physical atomic force field, and apply this construct to twelve mutants spanning the sequence variation between GA and GB. In agreement with experiment, we observe conformational switching from GA to GB upon a single L45Y substitution in the GA98 mutant. In line with the latent evolutionary potential concept, our model shows a gradual sequence-dependent change in fold preference in the mutants before this switch. Our analysis also indicates that a sharp GA/GB switch may arise from the orientation dependence of aromatic π-interactions. These findings provide physical insights toward rationalizing, predicting and designing evolutionary conformational switches. The biological functions of globular proteins are intimately related to their folded structures and their associated conformational fluctuations. Evolution of new structures is an important avenue to new functions. Although many mutations do not change the folded state, experiments indicate that a single amino acid substitution can lead to a drastic change in the folded structure. The physics of this switch-like behavior remains to be elucidated. Here we develop a computational model for the relevant physical forces, showing that mutations can lead to new folds by passing through intermediate sequences where the old and new folds occur with varying probabilities. Our approach helps provide a general physical account of conformational switching in evolution and mutational effects on conformational dynamics.
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Affiliation(s)
- Tobias Sikosek
- Departments of Biochemistry and Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Heinrich Krobath
- Departments of Biochemistry and Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Hue Sun Chan
- Departments of Biochemistry and Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
- * E-mail:
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16
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Tian P, Best RB. Structural Determinants of Misfolding in Multidomain Proteins. PLoS Comput Biol 2016; 12:e1004933. [PMID: 27163669 PMCID: PMC4862688 DOI: 10.1371/journal.pcbi.1004933] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2016] [Accepted: 04/21/2016] [Indexed: 12/02/2022] Open
Abstract
Recent single molecule experiments, using either atomic force microscopy (AFM) or Förster resonance energy transfer (FRET) have shown that multidomain proteins containing tandem repeats may form stable misfolded structures. Topology-based simulation models have been used successfully to generate models for these structures with domain-swapped features, fully consistent with the available data. However, it is also known that some multidomain protein folds exhibit no evidence for misfolding, even when adjacent domains have identical sequences. Here we pose the question: what factors influence the propensity of a given fold to undergo domain-swapped misfolding? Using a coarse-grained simulation model, we can reproduce the known propensities of multidomain proteins to form domain-swapped misfolds, where data is available. Contrary to what might be naively expected based on the previously described misfolding mechanism, we find that the extent of misfolding is not determined by the relative folding rates or barrier heights for forming the domains present in the initial intermediates leading to folded or misfolded structures. Instead, it appears that the propensity is more closely related to the relative stability of the domains present in folded and misfolded intermediates. We show that these findings can be rationalized if the folded and misfolded domains are part of the same folding funnel, with commitment to one structure or the other occurring only at a relatively late stage of folding. Nonetheless, the results are still fully consistent with the kinetic models previously proposed to explain misfolding, with a specific interpretation of the observed rate coefficients. Finally, we investigate the relation between interdomain linker length and misfolding, and propose a simple alchemical model to predict the propensity for domain-swapped misfolding of multidomain proteins.
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Affiliation(s)
- Pengfei Tian
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Robert B. Best
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, United States of America
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17
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Lapidus LJ, Acharya S, Schwantes CR, Wu L, Shukla D, King M, DeCamp SJ, Pande VS. Complex pathways in folding of protein G explored by simulation and experiment. Biophys J 2015; 107:947-55. [PMID: 25140430 DOI: 10.1016/j.bpj.2014.06.037] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 06/16/2014] [Accepted: 06/18/2014] [Indexed: 01/28/2023] Open
Abstract
The B1 domain of protein G has been a classic model system of folding for decades, the subject of numerous experimental and computational studies. Most of the experimental work has focused on whether the protein folds via an intermediate, but the evidence is mostly limited to relatively slow kinetic observations with a few structural probes. In this work we observe folding on the submillisecond timescale with microfluidic mixers using a variety of probes including tryptophan fluorescence, circular dichroism, and photochemical oxidation. We find that each probe yields different kinetics and compare these observations with a Markov State Model constructed from large-scale molecular dynamics simulations and find a complex network of states that yield different kinetics for different observables. We conclude that there are many folding pathways before the final folding step and that these paths do not have large free energy barriers.
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Affiliation(s)
- Lisa J Lapidus
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan.
| | - Srabasti Acharya
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan
| | | | - Ling Wu
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan
| | - Diwakar Shukla
- Department of Chemistry, Stanford University, Stanford, California; Simbios Program, Stanford University, Stanford, California
| | - Michael King
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan
| | - Stephen J DeCamp
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan
| | - Vijay S Pande
- Department of Chemistry, Stanford University, Stanford, California; Simbios Program, Stanford University, Stanford, California; Department of Structural Biology, Stanford University, Stanford, California; Biophysics Program, Stanford University, Stanford, California; Department of Computer Science, Stanford University, Stanford, California
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18
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Abstract
The intracellular milieu differs from the dilute conditions in which most biophysical and biochemical studies are performed. This difference has led both experimentalists and theoreticians to tackle the challenging task of understanding how the intracellular environment affects the properties of biopolymers. Despite a growing number of in-cell studies, there is a lack of quantitative, residue-level information about equilibrium thermodynamic protein stability under nonperturbing conditions. We report the use of NMR-detected hydrogen-deuterium exchange of quenched cell lysates to measure individual opening free energies of the 56-aa B1 domain of protein G (GB1) in living Escherichia coli cells without adding destabilizing cosolutes or heat. Comparisons to dilute solution data (pH 7.6 and 37 °C) show that opening free energies increase by as much as 1.14 ± 0.05 kcal/mol in cells. Importantly, we also show that homogeneous protein crowders destabilize GB1, highlighting the challenge of recreating the cellular interior. We discuss our findings in terms of hard-core excluded volume effects, charge-charge GB1-crowder interactions, and other factors. The quenched lysate method identifies the residues most important for folding GB1 in cells, and should prove useful for quantifying the stability of other globular proteins in cells to gain a more complete understanding of the effects of the intracellular environment on protein chemistry.
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19
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Sugita M, Kikuchi T. Analyses of the folding properties of ferredoxin-like fold proteins by means of a coarse-grained Gō model: relationship between the free energy profiles and folding cores. Proteins 2013; 82:954-65. [PMID: 24214655 DOI: 10.1002/prot.24469] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2013] [Revised: 09/30/2013] [Accepted: 10/29/2013] [Indexed: 11/07/2022]
Abstract
The folding mechanisms of proteins with multi-state transitions, the role of the intermediate states, and the precise mechanism how each transition occurs are significant on-going research issues. In this study, we investigate ferredoxin-like fold proteins which have a simple topology and multi-state transitions. We analyze the folding processes by means of a coarse-grained Gō model. We are able to reproduce the differences in the folding mechanisms between U1A, which has a high-free-energy intermediate state, and ADA2h and S6, which fold into the native structure through two-state transitions. The folding pathways of U1A, ADA2h, S6, and the S6 circular permutant, S6_p54-55, are reproduced and compared with experimental observations. We show that the ferredoxin-like fold contains two common regions consisting folding cores as predicted in other studies and that U1A produces an intermediate state due to the distinct cooperative folding of each core. However, because one of the cores of S6 loses its cooperativity and the two cores of ADA2h are tightly coupled, these proteins fold into the native structure through a two-state mechanism.
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Affiliation(s)
- Masatake Sugita
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, Japan
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20
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Ruschak AM, Rose JD, Coughlin MP, Religa TL. Engineered solubility tag for solution NMR of proteins. Protein Sci 2013; 22:1646-54. [PMID: 23963792 DOI: 10.1002/pro.2337] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2013] [Revised: 08/06/2013] [Accepted: 08/08/2013] [Indexed: 12/29/2022]
Abstract
The low solubility of many proteins hinders large scale expression and purification as well as biophysical measurements. Here, we devised a general strategy to solubilize a protein by conjugating it at a solvent-exposed position to a 6 kDa protein that was re-engineered to be highly soluble. We applied this method to the CARD domain of Apoptosis-associated speck-like protein containing a CARD (ASC), which represents one member of a class of proteins that are notoriously prone to aggregation. Attachment of the tag to a cysteine residue, introduced by site-directed mutagenesis at its self-association interface, improved the solubility of the ASC CARD over 50-fold under physiological conditions. Although it is not possible to use nuclear magnetic resonance (NMR) to obtain a high quality 2D correlation spectrum of the wild type domain under physiological conditions, we demonstrate that NMR relaxation parameters of the solubilized variant are sufficiently improved to facilitate virtually any demanding measurement. The method shown here represents a straightforward approach for dramatically increasing protein solubility, enabled by ease of labeling as well as flexibility in tag placement with minimal perturbation to the target.
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Affiliation(s)
- Amy M Ruschak
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, 44106
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21
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Glyakina AV, Likhachev IV, Balabaev NK, Galzitskaya OV. Right- and left-handed three-helix proteins. II. Similarity and differences in mechanical unfolding of proteins. Proteins 2013; 82:90-102. [PMID: 23873665 DOI: 10.1002/prot.24373] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Revised: 06/26/2013] [Accepted: 07/09/2013] [Indexed: 11/11/2022]
Abstract
Here, we study mechanical properties of eight 3-helix proteins (four right-handed and four left-handed ones), which are similar in size under stretching at a constant speed and at a constant force on the atomic level using molecular dynamics simulations. The analysis of 256 trajectories from molecular dynamics simulations with explicit water showed that the right-handed three-helix domains are more mechanically resistant than the left-handed domains. Such results are observed at different extension velocities studied (192 trajectories obtained at the following conditions: v = 0.1, 0.05, and 0.01 Å ps(-1) , T = 300 K) and under constant stretching force (64 trajectories, F = 800 pN, T = 300 K). We can explain this by the fact, at least in part, that the right-handed domains have a larger number of contacts per residue and the radius of cross section than the left-handed domains.
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Affiliation(s)
- Anna V Glyakina
- Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia; Institute of Mathematical Problems of Biology, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia
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22
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Granata D, Camilloni C, Vendruscolo M, Laio A. Characterization of the free-energy landscapes of proteins by NMR-guided metadynamics. Proc Natl Acad Sci U S A 2013; 110:6817-22. [PMID: 23572592 PMCID: PMC3637744 DOI: 10.1073/pnas.1218350110] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The use of free-energy landscapes rationalizes a wide range of aspects of protein behavior by providing a clear illustration of the different states accessible to these molecules, as well as of their populations and pathways of interconversion. The determination of the free-energy landscapes of proteins by computational methods is, however, very challenging as it requires an extensive sampling of their conformational spaces. We describe here a technique to achieve this goal with relatively limited computational resources by incorporating nuclear magnetic resonance (NMR) chemical shifts as collective variables in metadynamics simulations. As in this approach the chemical shifts are not used as structural restraints, the resulting free-energy landscapes correspond to the force fields used in the simulations. We illustrate this approach in the case of the third Ig-binding domain of protein G from streptococcal bacteria (GB3). Our calculations reveal the existence of a folding intermediate of GB3 with nonnative structural elements. Furthermore, the availability of the free-energy landscape enables the folding mechanism of GB3 to be elucidated by analyzing the conformational ensembles corresponding to the native, intermediate, and unfolded states, as well as the transition states between them. Taken together, these results show that, by incorporating experimental data as collective variables in metadynamics simulations, it is possible to enhance the sampling efficiency by two or more orders of magnitude with respect to standard molecular dynamics simulations, and thus to estimate free-energy differences among the different states of a protein with a k(B)T accuracy by generating trajectories of just a few microseconds.
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Affiliation(s)
- Daniele Granata
- International School for Advanced Studies (SISSA), Trieste 34136, Italy; and
| | - Carlo Camilloni
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
| | - Michele Vendruscolo
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
| | - Alessandro Laio
- International School for Advanced Studies (SISSA), Trieste 34136, Italy; and
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23
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Cunningham TF, McGoff MS, Sengupta I, Jaroniec CP, Horne WS, Saxena S. High-resolution structure of a protein spin-label in a solvent-exposed β-sheet and comparison with DEER spectroscopy. Biochemistry 2012; 51:6350-9. [PMID: 22809334 DOI: 10.1021/bi300328w] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
X-ray crystallography has been a useful tool in the development of site-directed spin labeling by resolving rotamers of the nitroxide spin-label side chain in a variety of α-helical environments. In this work, the crystal structure of a doubly spin-labeled N8C/K28C mutant of the B1 immunoglobulin-binding domain of protein G (GB1) was solved. The double mutant formed a domain-swapped dimer under crystallization conditions. Two rotameric states of the spin-label were resolved at the solvent-exposed α-helical site, at residue 28; these are in good agreement with rotamers previously reported for helical structures. The second site, at residue 8 on an interior β-strand, shows the presence of three distinct solvent-exposed side-chain rotamers. One of these rotamers is rarely observed within crystal structures of R1 sites and suggests that the H(α) and S(δ) hydrogen bond that is common to α-helical sites is absent at this interior β-strand residue. Variable temperature continuous wave (CW) experiments of the β-strand site showed two distinct components that were correlated to the rotameric states observed in crystallography. Interestingly, the CW data at room temperature could be fit without the use of an order parameter, which is consistent with the lack of the H(α) and S(δ) interaction. Additionally, double electron electron resonance (DEER) spectroscopy was performed on the GB1 double mutant in its monomeric form and yielded a most probable interspin distance of 25 ± 1 Å. In order to evaluate the accuracy of the measured DEER distance, the rotamers observed in the crystal structure of the domain-swapped GB1 dimer were modeled into a high-resolution structure of the wild type monomeric GB1. The distances generated in the resulting GB1 structural models match the most probable DEER distance within ~2 Å. The results are interesting as they indicate by direct experimental measurement that the rotameric states of R1 found in this crystal provide a very close match to the most probable distance measured by DEER.
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Affiliation(s)
- Timothy F Cunningham
- Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, PA 15260, USA
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24
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Folding pathways of proteins with increasing degree of sequence identities but different structure and function. Proc Natl Acad Sci U S A 2012; 109:17772-6. [PMID: 22652570 DOI: 10.1073/pnas.1201794109] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Much experimental work has been devoted in comparing the folding behavior of proteins sharing the same fold but different sequence. The recent design of proteins displaying very high sequence identities but different 3D structure allows the unique opportunity to address the protein-folding problem from a complementary perspective. Here we explored by Φ-value analysis the pathways of folding of three different heteromorphic pairs, displaying increasingly high-sequence identity (namely, 30%, 77%, and 88%), but different structures called G(A) (a 3-α helix fold) and G(B) (an α/β fold). The analysis, based on 132 site-directed mutants, is fully consistent with the idea that protein topology is committed very early along the pathway of folding. Furthermore, data reveals that when folding approaches a perfect two-state scenario, as in the case of the G(A) domains, the structural features of the transition state appear very robust to changes in sequence composition. On the other hand, when folding is more complex and multistate, as for the G(B)s, there are alternative nuclei or accessible pathways that can be alternatively stabilized by altering the primary structure. The implications of our results in the light of previous work on the folding of different members belonging to the same protein family are discussed.
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25
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Chung HS, McHale K, Louis JM, Eaton WA. Single-molecule fluorescence experiments determine protein folding transition path times. Science 2012; 335:981-4. [PMID: 22363011 PMCID: PMC3878298 DOI: 10.1126/science.1215768] [Citation(s) in RCA: 303] [Impact Index Per Article: 25.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The transition path is the tiny fraction of an equilibrium molecular trajectory when a transition occurs as the free-energy barrier between two states is crossed. It is a single-molecule property that contains all the mechanistic information on how a process occurs. As a step toward observing transition paths in protein folding, we determined the average transition-path time for a fast- and a slow-folding protein from a photon-by-photon analysis of fluorescence trajectories in single-molecule Förster resonance energy transfer experiments. Whereas the folding rate coefficients differ by a factor of 10,000, the transition-path times differ by a factor of less than 5, which shows that a fast- and a slow-folding protein take almost the same time to fold when folding actually happens. A very simple model based on energy landscape theory can explain this result.
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Affiliation(s)
- Hoi Sung Chung
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health (NIH), Bethesda, MD 20892-0520, USA.
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