1
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Vila JA. Protein folding rate evolution upon mutations. Biophys Rev 2023; 15:661-669. [PMID: 37681091 PMCID: PMC10480377 DOI: 10.1007/s12551-023-01088-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2023] [Accepted: 06/24/2023] [Indexed: 09/09/2023] Open
Abstract
Despite the spectacular success of cutting-edge protein fold prediction methods, many critical questions remain unanswered, including why proteins can reach their native state in a biologically reasonable time. A satisfactory answer to this simple question could shed light on the slowest folding rate of proteins as well as how mutations-amino-acid substitutions and/or post-translational modifications-might affect it. Preliminary results indicate that (i) Anfinsen's dogma validity ensures that proteins reach their native state on a reasonable timescale regardless of their sequence or length, and (ii) it is feasible to determine the evolution of protein folding rates without accounting for epistasis effects or the mutational trajectories between the starting and target sequences. These results have direct implications for evolutionary biology because they lay the groundwork for a better understanding of why, and to what extent, mutations-a crucial element of evolution and a factor influencing it-affect protein evolvability. Furthermore, they may spur significant progress in our efforts to solve crucial structural biology problems, such as how a sequence encodes its folding.
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Affiliation(s)
- Jorge A. Vila
- IMASL-CONICET, Universidad Nacional de San Luis, Ejército de Los Andes 950, 5700 San Luis, Argentina
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2
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Bychkova VE, Dolgikh DA, Balobanov VA, Finkelstein AV. The Molten Globule State of a Globular Protein in a Cell Is More or Less Frequent Case Rather than an Exception. Molecules 2022; 27:molecules27144361. [PMID: 35889244 PMCID: PMC9319461 DOI: 10.3390/molecules27144361] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 07/01/2022] [Accepted: 07/03/2022] [Indexed: 02/01/2023] Open
Abstract
Quite a long time ago, Oleg B. Ptitsyn put forward a hypothesis about the possible functional significance of the molten globule (MG) state for the functioning of proteins. MG is an intermediate between the unfolded and the native state of a protein. Its experimental detection and investigation in a cell are extremely difficult. In the last decades, intensive studies have demonstrated that the MG-like state of some globular proteins arises from either their modifications or interactions with protein partners or other cell components. This review summarizes such reports. In many cases, MG was evidenced to be functionally important. Thus, the MG state is quite common for functional cellular proteins. This supports Ptitsyn’s hypothesis that some globular proteins may switch between two active states, rigid (N) and soft (MG), to work in solution or interact with partners.
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Affiliation(s)
- Valentina E. Bychkova
- Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia; (V.E.B.); (A.V.F.)
| | - Dmitry A. Dolgikh
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117871 Moscow, Russia;
| | - Vitalii A. Balobanov
- Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia; (V.E.B.); (A.V.F.)
- Correspondence:
| | - Alexei V. Finkelstein
- Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia; (V.E.B.); (A.V.F.)
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3
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Naganathan AN. Predicting and Simulating Mutational Effects on Protein Folding Kinetics. Methods Mol Biol 2022; 2376:373-386. [PMID: 34845621 DOI: 10.1007/978-1-0716-1716-8_21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Mutational perturbations of protein structures, i.e., phi-value analysis, are commonly employed to probe the extent of involvement of a particular residue in the rate-determining step(s) of folding. This generally involves the measurement of folding thermodynamic parameters and kinetic rate constants for the wild-type and mutant proteins. While computational approaches have been reasonably successful in understanding and predicting the effect of mutations on folding thermodynamics, it has been challenging to explore the same on kinetics due to confounding structural, energetic, and dynamic factors. Accordingly, the frequent observation of fractional phi-values (mean of ~0.3) has resisted a precise and consistent interpretation. Here, we describe how to construct, parameterize, and employ a simple one-dimensional free energy surface model that is grounded in the basic tenets of the energy landscape theory to predict and simulate the effect of mutations on folding kinetics. As a proof of principle, we simulate one-dimensional free energy profiles of 806 mutations from 24 different proteins employing just the experimental destabilization as input, reproduce the relative unfolding activation free energies with a correlation of 0.91, and show that the mean phi-value of 0.3 essentially corresponds to the extent of stabilization energy gained at the barrier top while folding.
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Affiliation(s)
- Athi N Naganathan
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai, India.
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4
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Grazioso R, García-Viñuales S, D'Abrosca G, Baglivo I, Pedone PV, Milardi D, Fattorusso R, Isernia C, Russo L, Malgieri G. The change of conditions does not affect Ros87 downhill folding mechanism. Sci Rep 2020; 10:21067. [PMID: 33273582 PMCID: PMC7713307 DOI: 10.1038/s41598-020-78008-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Accepted: 11/19/2020] [Indexed: 11/20/2022] Open
Abstract
Downhill folding has been defined as a unique thermodynamic process involving a conformations ensemble that progressively loses structure with the decrease of protein stability. Downhill folders are estimated to be rather rare in nature as they miss an energetically substantial folding barrier that can protect against aggregation and proteolysis. We have previously demonstrated that the prokaryotic zinc finger protein Ros87 shows a bipartite folding/unfolding process in which a metal binding intermediate converts to the native structure through a delicate barrier-less downhill transition. Significant variation in folding scenarios can be detected within protein families with high sequence identity and very similar folds and for the same sequence by varying conditions. For this reason, we here show, by means of DSC, CD and NMR, that also in different pH and ionic strength conditions Ros87 retains its partly downhill folding scenario demonstrating that, at least in metallo-proteins, the downhill mechanism can be found under a much wider range of conditions and coupled to other different transitions. We also show that mutations of Ros87 zinc coordination sphere produces a different folding scenario demonstrating that the organization of the metal ion core is determinant in the folding process of this family of proteins.
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Affiliation(s)
- Rinaldo Grazioso
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Via Vivaldi 43, 81100, Caserta, Italy
| | | | - Gianluca D'Abrosca
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Via Vivaldi 43, 81100, Caserta, Italy
| | - Ilaria Baglivo
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Via Vivaldi 43, 81100, Caserta, Italy
| | - Paolo Vincenzo Pedone
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Via Vivaldi 43, 81100, Caserta, Italy
| | - Danilo Milardi
- Institute of Crystallography-CNR, Via Paolo Gaifami 18, 95126, Catania, Italy
| | - Roberto Fattorusso
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Via Vivaldi 43, 81100, Caserta, Italy
| | - Carla Isernia
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Via Vivaldi 43, 81100, Caserta, Italy
| | - Luigi Russo
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Via Vivaldi 43, 81100, Caserta, Italy.
| | - Gaetano Malgieri
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Via Vivaldi 43, 81100, Caserta, Italy.
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5
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Subramanian S, Golla H, Divakar K, Kannan A, de Sancho D, Naganathan AN. Slow Folding of a Helical Protein: Large Barriers, Strong Internal Friction, or a Shallow, Bumpy Landscape? J Phys Chem B 2020; 124:8973-8983. [PMID: 32955882 PMCID: PMC7659034 DOI: 10.1021/acs.jpcb.0c05976] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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The rate at which a protein molecule
folds is determined by opposing
energetic and entropic contributions to the free energy that shape
the folding landscape. Delineating the extent to which they impact
the diffusional barrier-crossing events, including the magnitude of
internal friction and barrier height, has largely been a challenging
task. In this work, we extract the underlying thermodynamic and dynamic
contributions to the folding rate of an unusually slow-folding helical
DNA-binding domain, PurR, which shares the characteristics of ultrafast
downhill-folding proteins but nonetheless appears to exhibit an apparent
two-state equilibrium. We combine equilibrium spectroscopy, temperature-viscosity-dependent
kinetics, statistical mechanical modeling, and coarse-grained simulations
to show that the conformational behavior of PurR is highly heterogeneous
characterized by a large spread in melting temperatures, marginal
thermodynamic barriers, and populated partially structured states.
PurR appears to be at the threshold of disorder arising from frustrated
electrostatics and weak packing that in turn slows down folding due
to a shallow, bumpy landscape and not due to large thermodynamic barriers
or strong internal friction. Our work highlights how a strong temperature
dependence on the pre-exponential could signal a shallow landscape
and not necessarily a slow-folding diffusion coefficient, thus determining
the folding timescales of even millisecond folding proteins and hints
at possible structural origins for the shallow landscape.
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Affiliation(s)
- Sandhyaa Subramanian
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - Hemashree Golla
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - Kalivarathan Divakar
- Department of Biotechnology, National Institute of Technology Warangal, Warangal 506004, India
| | - Adithi Kannan
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - David de Sancho
- Polimero eta Material Aurreratuak: Fisika, Kimika eta Teknologia, Kimika Fakultatea, Euskal Herriko Unibertsitatea UPV/EHU, Donostia-San Sebastián 20080, Spain.,Donostia International Physics Center (DIPC), PK 1072, Donostia-San Sebastián 20080, Spain
| | - Athi N Naganathan
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
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6
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Bhattacharjee K, Gopi S, Naganathan AN. A Disordered Loop Mediates Heterogeneous Unfolding of an Ordered Protein by Altering the Native Ensemble. J Phys Chem Lett 2020; 11:6749-6756. [PMID: 32787218 DOI: 10.1021/acs.jpclett.0c01848] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The high flexibility of long disordered or partially structured loops in folded proteins allows for entropic stabilization of native ensembles. Destabilization of such loops could alter the native ensemble or promote alternate conformations within the native ensemble if the ordered regions themselves are held together weakly. This is particularly true of downhill folding systems that exhibit weak unfolding cooperativity. Here, we combine experimental and computational methods to probe the response of the native ensemble of a helical, downhill folding domain PDD, which harbors an 11-residue partially structured loop, to perturbations. Statistical mechanical modeling points to continuous structural changes on both temperature and mutational perturbations driven by entropic stabilization of partially structured conformations within the native ensemble. Long time-scale simulations of the wild-type protein and two mutants showcase a remarkable conformational switching behavior wherein the parallel helices in the wild-type protein sample an antiparallel orientation in the mutants, with the C-terminal helix and the loop connecting the helices displaying high flexibility, disorder, and non-native interactions. We validate these computational predictions via the anomalous fluorescence of a native tyrosine located at the interface of the helices. Our observations highlight the role of long loops in determining the unfolding mechanisms, sensitivity of the native ensembles to mutational perturbations and provide experimentally testable predictions that can be explored in even two-state folding systems.
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Affiliation(s)
- Kabita Bhattacharjee
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - Soundhararajan Gopi
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - Athi N Naganathan
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
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7
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Modulation of allosteric coupling by mutations: from protein dynamics and packing to altered native ensembles and function. Curr Opin Struct Biol 2018; 54:1-9. [PMID: 30268910 PMCID: PMC6420056 DOI: 10.1016/j.sbi.2018.09.004] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 08/13/2018] [Accepted: 09/10/2018] [Indexed: 01/12/2023]
Abstract
A large body of work has gone into understanding the effect of mutations on protein structure and function. Conventional treatments have involved quantifying the change in stability, activity and relaxation rates of the mutants with respect to the wild-type protein. However, it is now becoming increasingly apparent that mutational perturbations consistently modulate the packing and dynamics of a significant fraction of protein residues, even those that are located >10–15 Å from the mutated site. Such long-range modulation of protein features can distinctly tune protein stability and the native conformational ensemble contributing to allosteric modulation of function. In this review, I summarize a series of experimental and computational observations that highlight the incredibly pliable nature of proteins and their response to mutational perturbations manifested via the intra-protein interaction network. I highlight how an intimate understanding of mutational effects could pave the way for integrating stability, folding, cooperativity and even allostery within a single physical framework.
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8
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Gopi S, Paul S, Ranu S, Naganathan AN. Extracting the Hidden Distributions Underlying the Mean Transition State Structures in Protein Folding. J Phys Chem Lett 2018; 9:1771-1777. [PMID: 29565127 DOI: 10.1021/acs.jpclett.8b00538] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The inherent conflict between noncovalent interactions and the large conformational entropy of the polypeptide chain forces folding reactions and their mechanisms to deviate significantly from chemical reactions. Accordingly, measures of structure in the transition state ensemble (TSE) are strongly influenced by the underlying distributions of microscopic folding pathways that are challenging to discern experimentally. Here, we present a detailed analysis of 150,000 folding transition paths of five proteins at three different thermodynamic conditions from an experimentally consistent statistical mechanical model. We find that the underlying TSE structural distributions are rarely unimodal, and the average experimental measures arise from complex underlying distributions. Unfolding pathways also exhibit subtle differences from folding counterparts due to a combination of Hammond behavior and native-state movements. Local interactions and topological complexity, to a lesser extent, are found to determine pathway heterogeneity, underscoring the importance of the balance between local and nonlocal energetics in protein folding.
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9
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Chu X, Muñoz V. Roles of conformational disorder and downhill folding in modulating protein-DNA recognition. Phys Chem Chem Phys 2018; 19:28527-28539. [PMID: 29044255 DOI: 10.1039/c7cp04380e] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Transcription factors are thought to efficiently search for their target DNA site via a combination of conventional 3D diffusion and 1D diffusion along the DNA molecule mediated by non-specific electrostatic interactions. This process requires the DNA-binding protein to quickly exchange between a search competent and a target recognition mode, but little is known as to how these two binding modes are encoded in the conformational properties of the protein. Here, we investigate this issue on the engrailed homeodomain (EngHD), a DNA-binding domain that folds ultrafast and exhibits a complex conformational behavior consistent with the downhill folding scenario. We explore the interplay between folding and DNA recognition using a coarse-grained computational model that allows us to manipulate the folding properties of the protein and monitor its non-specific and specific binding to DNA. We find that conformational disorder increases the search efficiency of EngHD by promoting a fast gliding search mode in addition to sliding. When gliding, EngHD remains loosely bound to DNA moving linearly along its length. A partially disordered EngHD also binds more dynamically to the target site, reducing the half-life of the specific complex via a spring-loaded mechanism. These findings apply to all conditions leading to partial disorder. However, we also find that at physiologically relevant temperatures EngHD is well folded and can only obtain the conformational flexibility required to accelerate 1D diffusion when it folds/unfolds within the downhill scenario (crossing a marginal free energy barrier). In addition, the conformational flexibility of native downhill EngHD enables its fast reconfiguration to lock into the specific binding site upon arrival, thereby affording finer control of the on- and off-rates of the specific complex. Our results provide key mechanistic insights into how DNA-binding domains optimize specific DNA recognition through the control of their conformational dynamics and folding mechanism.
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Affiliation(s)
- Xiakun Chu
- IMDEA Nanosciences, Faraday 9, Campus de Cantoblanco, Madrid, 28049, Spain
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10
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Munshi S, Naganathan AN. Imprints of function on the folding landscape: functional role for an intermediate in a conserved eukaryotic binding protein. Phys Chem Chem Phys 2016; 17:11042-52. [PMID: 25824585 DOI: 10.1039/c4cp06102k] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
In the computational characterization of single domain protein folding, the effective free energies of numerous microstates are projected onto few collective degrees of freedom that in turn serve as well-defined reaction coordinates. In this regard, one-dimensional (1D) free energy profiles are widely used mainly for their simplicity. Since folding and functional landscapes are interlinked, how well can these reduced representations capture the structural and dynamic features of functional states while being simultaneously consistent with experimental observables? We investigate this issue by characterizing the folding of the four-helix bundle bovine acyl-CoA binding protein (bACBP), which exhibits complex equilibrium and kinetic behaviours, employing an Ising-like statistical mechanical model and molecular simulations. We show that the features of the 1D free energy profile are sufficient to quantitatively reproduce multiple experimental observations including millisecond chevron-like kinetics and temperature dependence, a microsecond fast phase, barrier heights, unfolded state movements, the intermediate structure and average ϕ-values. Importantly, we find that the structural features of the native-like intermediate (partial disorder in helix 1) are intricately linked to a unique interplay between packing and electrostatics in this domain. By comparison with available experimental data, we propose that this intermediate determines the promiscuous functional behaviour of bACBP that exhibits broad substrate specificity. Our results present evidence to the possibility of employing the statistical mechanical model and the resulting 1D free energy profile to not just understand folding mechanisms but to even extract features of functionally relevant states and their energetic origins.
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Affiliation(s)
- Sneha Munshi
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India.
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11
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Naganathan AN, De Sancho D. Bridging Experiments and Native-Centric Simulations of a Downhill Folding Protein. J Phys Chem B 2015; 119:14925-33. [DOI: 10.1021/acs.jpcb.5b09568] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Athi N. Naganathan
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - David De Sancho
- CIC nanoGUNE, Tolosa Hiribidea,
76, E-20018 Donostia-San
Sebastián, Spain
- IKERBASQUE, Basque Foundation for Science, María Díaz de Haro 3, 48013 Bilbao, Spain
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12
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Naganathan AN, Muñoz V. Thermodynamics of Downhill Folding: Multi-Probe Analysis of PDD, a Protein that Folds Over a Marginal Free Energy Barrier. J Phys Chem B 2014; 118:8982-94. [DOI: 10.1021/jp504261g] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Athi N. Naganathan
- Department
of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai 600036, India
| | - Victor Muñoz
- Department
of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States
- Centro Nacional
de Biotecnología, Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain
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13
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Narayan A, Naganathan AN. Evidence for the sequential folding mechanism in RNase H from an ensemble-based model. J Phys Chem B 2014; 118:5050-8. [PMID: 24762044 DOI: 10.1021/jp500934f] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The number of distinct protein folding pathways starting from an unfolded ensemble, and hence, the folding mechanism is an intricate function of protein size, sequence complexity, and stability conditions. This has traditionally been a contentious issue particularly because of the ensemble nature of conventional experiments that can mask the complexity of the underlying folding landscape. Recent hydrogen-exchange experiments combined with mass spectrometry (HX-MS) reveal that the folding of RNase H proceeds in a hierarchical fashion with distinct intermediates and following a single discrete path. In our current work, we provide computational evidence for this unique folding mechanism by employing a structure-based statistical mechanical model. Upon calibrating the energetic terms of the model with equilibrium measurements, we predict multiple intermediate states in the folding of RNase H that closely resemble experimental observations. Remarkably, a simplified landscape representation adequately captures the folding complexity and predicts the possibility of a well-defined sequence of folding events. We supplement the statistical model study with both explicit solvent molecular simulations of the helical units and electrostatic calculations to provide structural and energetic insights into the early and late stages of RNase H folding that hint at the frustrated nature of its folding landscape.
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Affiliation(s)
- Abhishek Narayan
- Department of Biotechnology, Bhupat & Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras , Chennai 600036, India
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14
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Markiewicz BN, Yang L, Culik RM, Gao YQ, Gai F. How quickly can a β-hairpin fold from its transition state? J Phys Chem B 2014; 118:3317-25. [PMID: 24611730 PMCID: PMC3969101 DOI: 10.1021/jp500774q] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
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Understanding the structural nature
of the free energy bottleneck(s)
encountered in protein folding is essential to elucidating the underlying
dynamics and mechanism. For this reason, several techniques, including
Φ-value analysis, have previously been developed to infer the
structural characteristics of such high free-energy or transition
states. Herein we propose that one (or few) appropriately placed backbone
and/or side chain cross-linkers, such as disulfides, could be used
to populate a thermodynamically accessible conformational state that
mimics the folding transition state. Specifically, we test this hypothesis
on a model β-hairpin, Trpzip4, as its folding mechanism has
been extensively studied and is well understood. Our results show
that cross-linking the two β-strands near the turn region increases
the folding rate by an order of magnitude, to about (500 ns)−1, whereas cross-linking the termini results in a hyperstable β-hairpin
that has essentially the same folding rate as the uncross-linked peptide.
Taken together, these findings suggest that cross-linking is not only
a useful strategy to manipulate folding free energy barriers, as shown
in other studies, but also, in some cases, it can be used to stabilize
a folding transition state analogue and allow for direct assessment
of the folding process on the downhill side of the free energy barrier.
The calculated free energy landscape of the cross-linked Trpzip4 also
supports this picture. An empirical analysis further suggests, when
folding of β-hairpins does not involve a significant free energy
barrier, the folding time (τ) follows a power law dependence
on the number of hydrogen bonds to be formed (nH), namely, τ = τ0nHα, with
τ0 = 20 ns and α = 2.3.
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Affiliation(s)
- Beatrice N Markiewicz
- Department of Chemistry and ‡Department of Biochemistry and Biophysics, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
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15
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Deeg AA, Rampp MS, Popp A, Pilles BM, Schrader TE, Moroder L, Hauser K, Zinth W. Isomerization- and temperature-jump-induced dynamics of a photoswitchable β-hairpin. Chemistry 2013; 20:694-703. [PMID: 24415361 DOI: 10.1002/chem.201303189] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 10/28/2013] [Indexed: 11/09/2022]
Abstract
Conformational changes in proteins and peptides can be initiated by diverse processes. This raises the question how the variation of initiation mechanisms is connected to differences in folding or unfolding processes. In this work structural dynamics of a photoswitchable β-hairpin model peptide were initiated by two different mechanisms: temperature jump (T-jump) and isomerization of a backbone element. In both experiments the structural changes were followed by time-resolved IR spectroscopy in the nanosecond to microsecond range. When the photoisomerization of the azobenzene backbone switch initiated the folding reaction, pronounced absorption changes related to folding into the hairpin structure were found with a time constant of about 16 μs. In the T-jump experiment kinetics with the same time constant were observed. For both initiation processes the reaction dynamics revealed the same strong dependence of the reaction time on temperature. The highly similar transients in the microsecond range show that the peptide dynamics induced by T-jump and isomerization are both determined by the same mechanism and exclude a downhill-folding process. Furthermore, the combination of the two techniques allows a detailed model for folding and unfolding to be presented: The isomerization-induced folding process ends in a transition-state reaction scheme, in which a high energetic barrier of 48 kJ mol(-1) separates unfolded and folded structures.
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Affiliation(s)
- Andreas A Deeg
- Institute for BioMolecular Optics and Munich Center or Integrated Protein Science CIPSM, University of Munich, Oettingenstrasse 67, 80538 Munich (Germany), Fax: (+49) 89-2180-9202
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16
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Palmieri M, Malgieri G, Russo L, Baglivo I, Esposito S, Netti F, Del Gatto A, de Paola I, Zaccaro L, Pedone PV, Isernia C, Milardi D, Fattorusso R. Structural Zn(II) Implies a Switch from Fully Cooperative to Partly Downhill Folding in Highly Homologous Proteins. J Am Chem Soc 2013; 135:5220-8. [DOI: 10.1021/ja4009562] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Maddalena Palmieri
- Department of Environmental,
Biological and Pharmaceutical Science and Technology, Second University of Naples, Via Vivaldi 43, 81100
Caserta, Italy
| | - Gaetano Malgieri
- Department of Environmental,
Biological and Pharmaceutical Science and Technology, Second University of Naples, Via Vivaldi 43, 81100
Caserta, Italy
| | - Luigi Russo
- Department of Environmental,
Biological and Pharmaceutical Science and Technology, Second University of Naples, Via Vivaldi 43, 81100
Caserta, Italy
| | - Ilaria Baglivo
- Department of Environmental,
Biological and Pharmaceutical Science and Technology, Second University of Naples, Via Vivaldi 43, 81100
Caserta, Italy
| | - Sabrina Esposito
- Department of Environmental,
Biological and Pharmaceutical Science and Technology, Second University of Naples, Via Vivaldi 43, 81100
Caserta, Italy
| | - Fortuna Netti
- Department of Environmental,
Biological and Pharmaceutical Science and Technology, Second University of Naples, Via Vivaldi 43, 81100
Caserta, Italy
| | - Annarita Del Gatto
- Institute of Biostructures and Bioimaging-CNR (Naples), Via Mezzocannone 16, 80134
Naples, Italy
| | - Ivan de Paola
- Institute of Biostructures and Bioimaging-CNR (Naples), Via Mezzocannone 16, 80134
Naples, Italy
| | - Laura Zaccaro
- Institute of Biostructures and Bioimaging-CNR (Naples), Via Mezzocannone 16, 80134
Naples, Italy
| | - Paolo V. Pedone
- Department of Environmental,
Biological and Pharmaceutical Science and Technology, Second University of Naples, Via Vivaldi 43, 81100
Caserta, Italy
| | - Carla Isernia
- Department of Environmental,
Biological and Pharmaceutical Science and Technology, Second University of Naples, Via Vivaldi 43, 81100
Caserta, Italy
| | - Danilo Milardi
- Institute of Biostructures and Bioimaging-CNR (Catania), Viale A. Doria 6, 95125
Catania, Italy
| | - Roberto Fattorusso
- Department of Environmental,
Biological and Pharmaceutical Science and Technology, Second University of Naples, Via Vivaldi 43, 81100
Caserta, Italy
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17
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Sborgi L, Verma A, Muñoz V, de Alba E. Revisiting the NMR structure of the ultrafast downhill folding protein gpW from bacteriophage λ. PLoS One 2011; 6:e26409. [PMID: 22087227 PMCID: PMC3208555 DOI: 10.1371/journal.pone.0026409] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2011] [Accepted: 09/26/2011] [Indexed: 11/18/2022] Open
Abstract
GpW is a 68-residue protein from bacteriophage λ that participates in virus head morphogenesis. Previous NMR studies revealed a novel α+β fold for this protein. Recent experiments have shown that gpW folds in microseconds by crossing a marginal free energy barrier (i.e., downhill folding). These features make gpW a highly desirable target for further experimental and computational folding studies. As a step in that direction, we have re-determined the high-resolution structure of gpW by multidimensional NMR on a construct that eliminates the purification tags and unstructured C-terminal tail present in the prior study. In contrast to the previous work, we have obtained a full manual assignment and calculated the structure using only unambiguous distance restraints. This new structure confirms the α+β topology, but reveals important differences in tertiary packing. Namely, the two α-helices are rotated along their main axis to form a leucine zipper. The β-hairpin is orthogonal to the helical interface rather than parallel, displaying most tertiary contacts through strand 1. There also are differences in secondary structure: longer and less curved helices and a hairpin that now shows the typical right-hand twist. Molecular dynamics simulations starting from both gpW structures, and calculations with CS-Rosetta, all converge to our gpW structure. This confirms that the original structure has strange tertiary packing and strained secondary structure. A comparison of NMR datasets suggests that the problems were mainly caused by incomplete chemical shift assignments, mistakes in NOE assignment and the inclusion of ambiguous distance restraints during the automated procedure used in the original study. The new gpW corrects these problems, providing the appropriate structural reference for future work. Furthermore, our results are a cautionary tale against the inclusion of ambiguous experimental information in the determination of protein structures.
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Affiliation(s)
- Lorenzo Sborgi
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain
| | - Abhinav Verma
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain
| | - Victor Muñoz
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, United States of America
- * E-mail: (EdA); (VM)
| | - Eva de Alba
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain
- * E-mail: (EdA); (VM)
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18
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Naganathan AN, Perez-Jimenez R, Muñoz V, Sanchez-Ruiz JM. Estimation of protein folding free energy barriers from calorimetric data by multi-model Bayesian analysis. Phys Chem Chem Phys 2011; 13:17064-76. [PMID: 21769353 DOI: 10.1039/c1cp20156e] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The realization that folding free energy barriers can be small enough to result in significant population of the species at the barrier top has sprouted in several methods to estimate folding barriers from equilibrium experiments. Some of these approaches are based on fitting the experimental thermogram measured by differential scanning calorimetry (DSC) to a one-dimensional representation of the folding free-energy surface (FES). Different physical models have been used to represent the FES: (1) a Landau quartic polynomial as a function of the total enthalpy, which acts as an order parameter; (2) the projection onto a structural order parameter (i.e. number of native residues or native contacts) of the free energy of all the conformations generated by Ising-like statistical mechanical models; and (3) mean-field models that define conformational entropy and stabilization energy as functions of a continuous local order parameter. The fundamental question that emerges is how can we obtain robust, model-independent estimates of the thermodynamic folding barrier from the analysis of DSC experiments. Here we address this issue by comparing the performance of various FES models in interpreting the thermogram of a protein with a marginal folding barrier. We chose the small α-helical protein PDD, which folds-unfolds in microseconds crossing a free energy barrier previously estimated as ~1 RT. The fits of the PDD thermogram to the various models and assumptions produce FES with a consistently small free energy barrier separating the folded and unfolded ensembles. However, the fits vary in quality as well as in the estimated barrier. Applying Bayesian probabilistic analysis we rank the fit performance using a statistically rigorous criterion that leads to a global estimate of the folding barrier and its precision, which for PDD is 1.3 ± 0.4 kJ mol(-1). This result confirms that PDD folds over a minor barrier consistent with the downhill folding regime. We have further validated the multi-model Bayesian approach through the analysis of two additional protein systems: gpW, a midsize single-domain with α + β topology that also folds in microseconds and has been previously catalogued as a downhill folder, and α-spectrin SH3, a domain of similar size but with a β-barrel fold, slow-folding kinetics and two-state-like thermodynamics. From a general viewpoint, the Bayesian analysis developed here results in a statistically robust, virtually model-independent, method to estimate the thermodynamic free-energy barriers to protein folding from DSC thermograms. Our method appears to be sufficiently accurate to consistently detect small differences in the barrier height, and thus opens up the possibility of characterizing experimentally the changes in thermodynamic folding barriers induced by single-point mutations on proteins within the downhill regime.
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Affiliation(s)
- Athi N Naganathan
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (CSIC), Ramiro de Maeztu 9, Madrid 28040, Spain
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19
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Naganathan AN, Orozco M. The protein folding transition-state ensemble from a Gō-like model. Phys Chem Chem Phys 2011; 13:15166-74. [DOI: 10.1039/c1cp20964g] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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20
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Naganathan AN, Li P, Perez-Jimenez R, Sanchez-Ruiz JM, Muñoz V. Navigating the downhill protein folding regime via structural homologues. J Am Chem Soc 2010; 132:11183-90. [PMID: 20698685 DOI: 10.1021/ja103612q] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Proteins that fold over free-energy barriers <or= 3RT are classified as downhill folders. This regime is characterized by equilibrium unfolding that is proportionally broader and more complex the lower the folding barrier. Downhill proteins are also expected to fold up in a few microseconds. However, the relationship between rate and equilibrium signatures is affected by other factors such as protein size and folding topology. Here we perform a direct comparison of the kinetics and equilibrium unfolding of two structural homologues: BBL and PDD. BBL folds-unfolds in just approximately 1 micros at 335 K and displays the equilibrium signatures expected for a protein at the bottom of the downhill folding regime. PDD, which has the same 3D structure and size, folds-unfolds approximately 8 times more slowly and, concomitantly, exhibits all the downhill equilibrium signatures to a lesser degree. Our results demonstrate that the equilibrium signatures of downhill folding are proportional to the changes in folding rate once structural and size-scaling effects are factored out. This conclusion has two important implications: (1) it confirms that the quantitative analysis of equilibrium experiments in ultrafast folding proteins does provide direct information about free-energy barriers, a result that is incompatible with the conventional view of protein folding as a highly activated process, and (2) it advocates for equilibrium-kinetic studies of homologous proteins as a powerful tool to navigate the downhill folding regime via comparative analysis. The latter should prove extremely useful for the investigation of sequence, functional, and evolutionary determinants of protein folding barriers.
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Affiliation(s)
- Athi N Naganathan
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas (CSIC), Ramiro de Maeztu 9, Madrid 28040, Spain
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21
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Desai TM, Cerminara M, Sadqi M, Muñoz V. The effect of electrostatics on the marginal cooperativity of an ultrafast folding protein. J Biol Chem 2010; 285:34549-56. [PMID: 20729560 DOI: 10.1074/jbc.m110.154021] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proteins fold up by coordinating the different segments of their polypeptide chain through a network of weak cooperative interactions. Such cooperativity results in unfolding curves that are typically sigmoidal. However, we still do not know what factors modulate folding cooperativity or the minimal amount that ensures folding into specific three-dimensional structures. Here, we address these issues on BBL, a small helical protein that folds in microseconds via a marginally cooperative downhill process (Li, P., Oliva, F. Y., Naganathan, A. N., and Muñoz, V. (2009) Proc. Natl. Acad. Sci. USA. 106, 103-108). Particularly, we explore the effects of salt-induced screening of the electrostatic interactions in BBL at neutral pH and in acid-denatured BBL. Our results show that electrostatic screening stabilizes the native state of the neutral and protonated forms, inducing complete refolding of acid-denatured BBL. Furthermore, without net electrostatic interactions, the unfolding process becomes much less cooperative, as judged by the broadness of the equilibrium unfolding curve and the relaxation rate. Our experiments show that the marginally cooperative unfolding of BBL can still be made twice as broad while the protein retains its ability to fold into the native three-dimensional structure in microseconds. This result demonstrates experimentally that efficient folding does not require cooperativity, confirming predictions from theory and computer simulations and challenging the conventional biochemical paradigm. Furthermore, we conclude that electrostatic interactions are an important factor in determining folding cooperativity. Thus, electrostatic modulation by pH-salt and/or mutagenesis of charged residues emerges as an attractive tool for tuning folding cooperativity.
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Affiliation(s)
- Tanay M Desai
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, Madrid 28040, Spain
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22
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Insights into protein folding mechanisms from large scale analysis of mutational effects. Proc Natl Acad Sci U S A 2010; 107:8611-6. [PMID: 20418505 DOI: 10.1073/pnas.1000988107] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protein folding mechanisms are probed experimentally using single-point mutant perturbations. The relative effects on the folding (phi-values) and unfolding (1 - phi) rates are used to infer the detailed structure of the transition-state ensemble (TSE). Here we analyze kinetic data on > 800 mutations carried out for 24 proteins with simple kinetic behavior. We find two surprising results: (i) all mutant effects are described by the equation: DeltaDeltaG(double dagger)(unfold)=0.76DeltaDeltaG(eq) +/- 1.8kJ/mol. Therefore all data are consistent with a single phi-value (0.24) with accuracy comparable to experimental precision, suggesting that the structural information in conventional phi-values is low. (ii) phi-values change with stability, increasing in mean value and spread from native to unfolding conditions, and thus cannot be interpreted without proper normalization. We eliminate stability effects calculating the phi-values at the mutant denaturation midpoints; i.e., conditions of zero stability (phi(0)). We then show that the intrinsic variability is phi(0) = 0.36 +/- 0.11, being somewhat larger for beta-sheet-rich proteins than for alpha-helical proteins. Importantly, we discover that phi(0)-values are proportional to how many of the residues surrounding the mutated site are local in sequence. High phi(0)-values correspond to protein surface sites, which have few nonlocal neighbors, whereas core residues with many tertiary interactions produce the lowest phi(0)-values. These results suggest a general mechanism in which the TSE at zero stability is a broad conformational ensemble stabilized by local interactions and without specific tertiary interactions, reconciling phi-values with many other empirical observations.
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23
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Wu L, Li WF, Liu F, Zhang J, Wang J, Wang W. Understanding protein folding cooperativity based on topological consideration. J Chem Phys 2009; 131:065105. [PMID: 19691415 DOI: 10.1063/1.3200952] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The folding cooperativity is an important issue of protein folding dynamics. Since the native topology plays a significant role in determining the folding behavior of proteins, we believe that it also has close relationship with the folding cooperativity. In the present work, we perform simulations on proteins Naf-BBL, QNND-BBL, CI2, and SH3 with the Gō model and compare their different folding behaviors. By analyzing the weak cooperative folding of protein Naf-BBL in detail, we found that the folding of Naf-BBL shows relatively weak thermodynamic coupling between residues, and such weak coupling is found mainly between the nonlocal native contacts. This finding complements our understandings on the source of barrierless folding of Naf-BBL and promotes us to analyze the topological origins of the poor thermodynamic coupling of Naf-BBL. Then, we further extend our analysis to other two-state and multistate proteins. Based on the considerations of the thermodynamic coupling and kinetic coupling, we conclude that the fraction of scattered native contacts, the difference in loop entropy of contacts, and the long range relative contact order are the major topological factors that influence the folding cooperativity. The combination of these three tertiary structural features shows significant correlations with the folding types of proteins. Moreover, we also discuss the topological factors related to downhill folding. Finally, the generic role of tertiary structure in determining the folding cooperativity is summarized.
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Affiliation(s)
- L Wu
- Department of Physics and National Laboratory of Solid State Microstructure, Nanjing University, Nanjing 210093, China
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