1
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Campos LA, Muñoz V. Targeting the protein folding transition state by mutation: Large scale (un)folding rate accelerations without altering native stability. Protein Sci 2024; 33:e5031. [PMID: 38864692 PMCID: PMC11168068 DOI: 10.1002/pro.5031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Revised: 05/06/2024] [Accepted: 05/09/2024] [Indexed: 06/13/2024]
Abstract
Proteins are constantly undergoing folding and unfolding transitions, with rates that determine their homeostasis in vivo and modulate their biological function. The ability to optimize these rates without affecting overall native stability is hence highly desirable for protein engineering and design. The great challenge is, however, that mutations generally affect folding and unfolding rates with inversely complementary fractions of the net free energy change they inflict on the native state. Here we address this challenge by targeting the folding transition state (FTS) of chymotrypsin inhibitor 2 (CI2), a very slow and stable two-state folding protein with an FTS known to be refractory to change by mutation. We first discovered that the CI2's FTS is energetically taxed by the desolvation of several, highly conserved, charges that form a buried salt bridge network in the native structure. Based on these findings, we designed a CI2 variant that bears just four mutations and aims to selectively stabilize the FTS. This variant has >250-fold faster rates in both directions and hence identical native stability, demonstrating the success of our FTS-centric design strategy. With an optimized FTS, CI2 also becomes 250-fold more sensitive to proteolytic degradation by its natural substrate chymotrypsin, and completely loses its activity as inhibitor. These results indicate that CI2 has been selected through evolution to have a very unstable FTS in order to attain the kinetic stability needed to effectively function as protease inhibitor. Moreover, the CI2 case showcases that protein (un)folding rates can critically pivot around a few key residues-interactions, which can strongly modify the general effects of known structural factors such as domain size and fold topology. From a practical standpoint, our results suggest that future efforts should perhaps focus on identifying such critical residues-interactions in proteins as best strategy to significantly improve our ability to predict and engineer protein (un)folding rates.
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Affiliation(s)
- Luis A. Campos
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia)MadridSpain
- Unidad de Nanobiotecnología Asociada al Centro Nacional de Biotecnología (CSIC)MadridSpain
| | - Victor Muñoz
- Department of BioengineeringUniversity of CaliforniaMercedCaliforniaUSA
- Center for Cellular and Biomolecular MachinesUniversity of CaliforniaMercedCaliforniaUSA
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2
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Qing R, Hao S, Smorodina E, Jin D, Zalevsky A, Zhang S. Protein Design: From the Aspect of Water Solubility and Stability. Chem Rev 2022; 122:14085-14179. [PMID: 35921495 PMCID: PMC9523718 DOI: 10.1021/acs.chemrev.1c00757] [Citation(s) in RCA: 56] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Indexed: 12/13/2022]
Abstract
Water solubility and structural stability are key merits for proteins defined by the primary sequence and 3D-conformation. Their manipulation represents important aspects of the protein design field that relies on the accurate placement of amino acids and molecular interactions, guided by underlying physiochemical principles. Emulated designer proteins with well-defined properties both fuel the knowledge-base for more precise computational design models and are used in various biomedical and nanotechnological applications. The continuous developments in protein science, increasing computing power, new algorithms, and characterization techniques provide sophisticated toolkits for solubility design beyond guess work. In this review, we summarize recent advances in the protein design field with respect to water solubility and structural stability. After introducing fundamental design rules, we discuss the transmembrane protein solubilization and de novo transmembrane protein design. Traditional strategies to enhance protein solubility and structural stability are introduced. The designs of stable protein complexes and high-order assemblies are covered. Computational methodologies behind these endeavors, including structure prediction programs, machine learning algorithms, and specialty software dedicated to the evaluation of protein solubility and aggregation, are discussed. The findings and opportunities for Cryo-EM are presented. This review provides an overview of significant progress and prospects in accurate protein design for solubility and stability.
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Affiliation(s)
- Rui Qing
- State
Key Laboratory of Microbial Metabolism, School of Life Sciences and
Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China
- Media
Lab, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
- The
David H. Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Shilei Hao
- Media
Lab, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
- Key
Laboratory of Biorheological Science and Technology, Ministry of Education, College of Bioengineering, Chongqing University, Chongqing 400030, China
| | - Eva Smorodina
- Department
of Immunology, University of Oslo and Oslo
University Hospital, Oslo 0424, Norway
| | - David Jin
- Avalon GloboCare
Corp., Freehold, New Jersey 07728, United States
| | - Arthur Zalevsky
- Laboratory
of Bioinformatics Approaches in Combinatorial Chemistry and Biology, Shemyakin−Ovchinnikov Institute of Bioorganic
Chemistry RAS, Moscow 117997, Russia
| | - Shuguang Zhang
- Media
Lab, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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3
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Kleiner D, Shapiro Tuchman Z, Shmulevich F, Shahar A, Zarivach R, Kosloff M, Bershtein S. Evolution of homo-oligomerization of methionine S-adenosyltransferases is replete with structure-function constrains. Protein Sci 2022; 31:e4352. [PMID: 35762725 PMCID: PMC9202080 DOI: 10.1002/pro.4352] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 04/14/2022] [Accepted: 05/07/2022] [Indexed: 11/16/2022]
Abstract
Homomers are prevalent in bacterial proteomes, particularly among core metabolic enzymes. Homomerization is often key to function and regulation, and interfaces that facilitate the formation of homomeric enzymes are subject to intense evolutionary change. However, our understanding of the molecular mechanisms that drive evolutionary variation in homomeric complexes is still lacking. How is the diversification of protein interfaces linked to variation in functional regulation and structural integrity of homomeric complexes? To address this question, we studied quaternary structure evolution of bacterial methionine S-adenosyltransferases (MATs)-dihedral homotetramers formed along a large and conserved dimeric interface harboring two active sites, and a small, recently evolved, interdimeric interface. Here, we show that diversity in the physicochemical properties of small interfaces is directly linked to variability in the kinetic stability of MAT quaternary complexes and in modes of their functional regulation. Specifically, hydrophobic interactions within the small interface of Escherichia coli MAT render the functional homotetramer kinetically stable yet impose severe aggregation constraints on complex assembly. These constraints are alleviated by electrostatic interactions that accelerate dimer-dimer assembly. In contrast, Neisseria gonorrhoeae MAT adopts a nonfunctional dimeric state due to the low hydrophobicity of its small interface and the high flexibility of its active site loops, which perturbs small interface integrity. Remarkably, in the presence of methionine and ATP, N. gonorrhoeae MAT undergoes substrate-induced assembly into a functional tetrameric state. We suggest that evolution acts on the interdimeric interfaces of MATs to tailor the regulation of their activity and stability to unique organismal needs.
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Affiliation(s)
- Daniel Kleiner
- Department of Life SciencesBen‐Gurion University of the NegevBeer‐ShevaIsrael
| | - Ziva Shapiro Tuchman
- The Department of Human Biology, Faculty of Natural SciencesUniversity of HaifaHaifaIsrael
| | - Fannia Shmulevich
- Department of Life SciencesBen‐Gurion University of the NegevBeer‐ShevaIsrael
| | - Anat Shahar
- Ilse Katz Institute for Nanoscale Science & TechnologyBen‐Gurion University of the NegevBeer‐ShevaIsrael
| | - Raz Zarivach
- Department of Life SciencesBen‐Gurion University of the NegevBeer‐ShevaIsrael
- Macromolecular Crystallography and Cryo‐EM Research Center, The National Institute for Biotechnology in the NegevBen‐Gurion University of the NegevBeer‐ShevaIsrael
| | - Mickey Kosloff
- The Department of Human Biology, Faculty of Natural SciencesUniversity of HaifaHaifaIsrael
| | - Shimon Bershtein
- Department of Life SciencesBen‐Gurion University of the NegevBeer‐ShevaIsrael
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4
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Nandi T, Ainavarapu SRK. Native Salt Bridges Are a Key Regulator of Ubiquitin's Mechanical Stability. J Phys Chem B 2022; 126:3505-3511. [PMID: 35535497 DOI: 10.1021/acs.jpcb.2c00972] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Although it is known that various intramolecular interactions determine protein mechanical stability, a detailed molecular-level understanding of the key regulators of protein mechanical stability is still lacking. Here, we present evidence for salt bridges in ubiquitin as important intramolecular interactions that can affect protein mechanical stability. Ubiquitin has two salt bridges: one relatively surface-exposed (SB1:K11-E34) and the other relatively buried (SB2:K27-D52). Ubiquitin is a reversible post-translational modifier and is stable mechanically (Favgu = 185 pN). On breaking SB1, the mechanical stability of ubiquitin is slightly enhanced (Favgu = 193 pN). In contrast, the mechanical stability significantly decreased upon breaking SB2 (Favgu = 158 pN). These results suggest that SB1 are SB2 are regulators of the mechanical stability of ubiquitin. Interestingly, the mechanical stability decreased further (Favgu = 145 pN) for the double salt bridge (DB) null variant. Monte Carlo simulations elucidate that the main regulating factor is the spontaneous unfolding rate constant (ku0), being the highest for the DB null variant followed by the SB2 null variant, and it remains unaltered for the SB1 null variant, while the native-to-transition-state distance (xu) remains unchanged. Our study provides mechanistic understanding on how two native salt bridges can independently regulate the mechanical stability in a protein, which has implications in designing protein-based robust biomaterials in the future.
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Affiliation(s)
- Tathagata Nandi
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Sri Rama Koti Ainavarapu
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai 400005, India
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5
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Lee YR, Kwon S, Sung BJ. The non-classical kinetics and the mutual information of polymer loop formation. J Chem Phys 2020; 152:184905. [PMID: 32414275 DOI: 10.1063/5.0005453] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The loop formation of a single polymer chain has served as a model system for various biological and chemical processes. Theories based on the Smoluchowski equation proposed that the rate constant (kloop) of the loop formation would be inversely proportional to viscosity (η), i.e., kloop ∼ η-1. Experiments and simulations showed, however, that kloop showed the fractional viscosity dependence of kloop ∼ η-β with β < 1 either in glasses or in low-viscosity solutions. The origin of the fractional viscosity dependence remains elusive and has been attributed to phenomenological aspects. In this paper, we illustrate that the well-known failure of classical kinetics of the loop formation results from the breakdown of the local thermal equilibrium (LTE) approximation and that the mutual information can quantify the breakdown of the LTE successfully.
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Affiliation(s)
- Young-Ro Lee
- Department of Chemistry, Sogang University, Seoul 04107, South Korea
| | - Seulki Kwon
- Department of Chemistry, Sogang University, Seoul 04107, South Korea
| | - Bong June Sung
- Department of Chemistry, Sogang University, Seoul 04107, South Korea
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6
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Nandi T, Desai A, Ainavarapu SRK. The unfolding transition state of ubiquitin with charged residues has higher energy than that with hydrophobic residues. Phys Chem Chem Phys 2020; 22:23158-23168. [DOI: 10.1039/d0cp03876h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The native-state structure and folding pathways of a protein are encoded in its amino acid sequence.
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Affiliation(s)
- Tathagata Nandi
- Department of Chemical Sciences
- Tata Institute of Fundamental Research
- Mumbai 400005
- India
| | - Amogh Desai
- Department of Chemical Sciences
- Tata Institute of Fundamental Research
- Mumbai 400005
- India
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7
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Bandyopadhyay AK, Islam RNU, Mitra D, Banerjee S, Goswami A. Stability of buried and networked salt-bridges (BNSB)in thermophilic proteins. Bioinformation 2019; 15:61-67. [PMID: 31360001 PMCID: PMC6651030 DOI: 10.6026/97320630015061] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2019] [Accepted: 02/02/2019] [Indexed: 11/23/2022] Open
Abstract
Thermophilic proteins function at high temperature, unlike mesophilic proteins. Thermo-stability of these proteins is due to the unique buried and networked salt-bridge (BNSB). However, it is known that the desolvation cost of BNSB is too high compared to other favorable energy terms. Nonetheless, it is known that stability is provided generally by hydrophobic isosteres without the need for BNSB. We show in this analysis that the BNSB is the optimal evolutionary design of salt-bridge to offset desolvation cost efficiently. Hence, thermophilic proteins with a high level of BNSB provide thermo-stability.
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Affiliation(s)
| | | | - Debanjan Mitra
- Department of Biotechnology, University of Burdwan, Burdwan, West Bengal,India
| | - Sahini Banerjee
- Department of Biological Sciences, ISI, Kolkata, West Bengal,India
| | - Arunava Goswami
- Department of Biological Sciences, ISI, Kolkata, West Bengal,India
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8
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Moulick R, Goluguri RR, Udgaonkar JB. Ruggedness in the Free Energy Landscape Dictates Misfolding of the Prion Protein. J Mol Biol 2019; 431:807-824. [DOI: 10.1016/j.jmb.2018.12.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 11/15/2018] [Accepted: 12/16/2018] [Indexed: 12/12/2022]
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9
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Yrazu FM, Pinamonti G, Clementi C. The Effect of Electrostatic Interactions on the Folding Kinetics of a 3-α-Helical Bundle Protein Family. J Phys Chem B 2018; 122:11800-11806. [PMID: 30277393 DOI: 10.1021/acs.jpcb.8b08676] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The trio of protein segment repeats called spectrins diverges by more than 2 orders of magnitude in their folding and unfolding rates, despite having very similar stabilities and almost coincidental topologies. Experimental studies revealed that the mutation of five particular residues dramatically alters the kinetic rates in the slow folders, making them similar to the rates of the fast folder. This is considered to be an exceptional behavior which seems in principle to challenge the current understanding of the protein folding process. In this work, we analyze this scenario, using a simplified computational model, combined with state-of-the-art kinetic analysis techniques. Our model faithfully separates the kinetics of the fast and slow folders and captures the effect of the five mutations. We show that the inclusion of electrostatics in the model is necessary to explain the experimental findings.
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Affiliation(s)
- Fernando Miguel Yrazu
- Department of Chemical and Biomolecular Engineering , Rice University , Houston , Texas 77005 , United States
| | - Giovanni Pinamonti
- Department of Informatics and Mathematics , Freie Universität Berlin , 14195 Berlin , Germany
| | - Cecilia Clementi
- Department of Chemical and Biomolecular Engineering , Rice University , Houston , Texas 77005 , United States.,Department of Informatics and Mathematics , Freie Universität Berlin , 14195 Berlin , Germany.,Center for Theoretical Biological Physics and Department of Chemistry , Rice University , Houston , Texas 77005 , United States
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10
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Arai M. Unified understanding of folding and binding mechanisms of globular and intrinsically disordered proteins. Biophys Rev 2018; 10:163-181. [PMID: 29307002 PMCID: PMC5899706 DOI: 10.1007/s12551-017-0346-7] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 11/13/2017] [Indexed: 12/18/2022] Open
Abstract
Extensive experimental and theoretical studies have advanced our understanding of the mechanisms of folding and binding of globular proteins, and coupled folding and binding of intrinsically disordered proteins (IDPs). The forces responsible for conformational changes and binding are common in both proteins; however, these mechanisms have been separately discussed. Here, we attempt to integrate the mechanisms of coupled folding and binding of IDPs, folding of small and multi-subdomain proteins, folding of multimeric proteins, and ligand binding of globular proteins in terms of conformational selection and induced-fit mechanisms as well as the nucleation–condensation mechanism that is intermediate between them. Accumulating evidence has shown that both the rate of conformational change and apparent rate of binding between interacting elements can determine reaction mechanisms. Coupled folding and binding of IDPs occurs mainly by induced-fit because of the slow folding in the free form, while ligand binding of globular proteins occurs mainly by conformational selection because of rapid conformational change. Protein folding can be regarded as the binding of intramolecular segments accompanied by secondary structure formation. Multi-subdomain proteins fold mainly by the induced-fit (hydrophobic collapse) mechanism, as the connection of interacting segments enhances the binding (compaction) rate. Fewer hydrophobic residues in small proteins reduce the intramolecular binding rate, resulting in the nucleation–condensation mechanism. Thus, the folding and binding of globular proteins and IDPs obey the same general principle, suggesting that the coarse-grained, statistical mechanical model of protein folding is promising for a unified theoretical description of all mechanisms.
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Affiliation(s)
- Munehito Arai
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo, 153-8902, Japan.
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11
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Kwon S, Cho HW, Kim J, Sung BJ. Fractional Viscosity Dependence of Reaction Kinetics in Glass-Forming Liquids. PHYSICAL REVIEW LETTERS 2017; 119:087801. [PMID: 28952769 DOI: 10.1103/physrevlett.119.087801] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Indexed: 06/07/2023]
Abstract
The diffusion of molecules in complex systems such as glasses and cell cytoplasm is slow, heterogeneous, and sometimes nonergodic. The effects of such intriguing diffusion on the kinetics of chemical and biological reactions remain elusive. In this Letter, we report that the kinetics of the polymer loop formation reaction in a Kob-Andersen (KA) glass forming liquid is influenced significantly by the dynamic heterogeneity. The diffusion coefficient D of a KA liquid deviates from the Stokes-Einstein relation at low temperatures and D shows a fractional dependence on the solvent viscosity η_{s}, i.e., D∼η_{s}^{-ξ_{D}} with ξ_{D}=0.85. The dynamic heterogeneity of a KA liquid affects the rate constant k_{rxn} of the loop formation and leads to the identical fractional dependence of k_{rxn} on η_{s} with k_{rxn}∼η_{s}^{-ξ} and ξ=ξ_{D}, contrary to reactions in dynamically homogeneous solutions where k_{rxn}∼η_{s}^{-1}.
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Affiliation(s)
- Seulki Kwon
- Department of Chemistry and Research Institute for Basic Science, Sogang University, Seoul 121-742, Republic of Korea
| | - Hyun Woo Cho
- Department of Chemistry and Research Institute for Basic Science, Sogang University, Seoul 121-742, Republic of Korea
| | - Jeongmin Kim
- Department of Chemistry and Research Institute for Basic Science, Sogang University, Seoul 121-742, Republic of Korea
| | - Bong June Sung
- Department of Chemistry and Research Institute for Basic Science, Sogang University, Seoul 121-742, Republic of Korea
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12
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Influence of Glu/Arg, Asp/Arg, and Glu/Lys Salt Bridges on α-Helical Stability and Folding Kinetics. Biophys J 2017; 110:2328-2341. [PMID: 27276251 DOI: 10.1016/j.bpj.2016.04.015] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Revised: 03/17/2016] [Accepted: 04/08/2016] [Indexed: 01/24/2023] Open
Abstract
Using a combination of ultraviolet circular dichroism, temperature-jump transient-infrared spectroscopy, and molecular dynamics simulations, we investigate the effect of salt bridges between different types of charged amino-acid residue pairs on α-helix folding. We determine the stability and the folding and unfolding rates of 12 alanine-based α-helical peptides, each of which has a nearly identical composition containing three pairs of positively and negatively charged residues (either Glu(-)/Arg(+), Asp(-)/Arg(+), or Glu(-)/Lys(+)). Within each set of peptides, the distance and order of the oppositely charged residues in the peptide sequence differ, such that they have different capabilities of forming salt bridges. Our results indicate that stabilizing salt bridges (in which the interacting residues are spaced and ordered such that they favor helix formation) speed up α-helix formation by up to 50% and slow down the unfolding of the α-helix, whereas salt bridges with an unfavorable geometry have the opposite effect. Comparing the peptides with different types of charge pairs, we observe that salt bridges between side chains of Glu(-) and Arg(+) are most favorable for the speed of folding, probably because of the larger conformational space of the salt-bridging Glu(-)/Arg(+) rotamer pairs compared to Asp(-)/Arg(+) and Glu(-)/Lys(+). We speculate that the observed impact of salt bridges on the folding kinetics might explain why some proteins contain salt bridges that do not stabilize the final, folded conformation.
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13
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Davis CM, Dyer RB. The Role of Electrostatic Interactions in Folding of β-Proteins. J Am Chem Soc 2016; 138:1456-64. [PMID: 26750867 DOI: 10.1021/jacs.5b13201] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Atomic-level molecular dynamic simulations are capable of fully folding structurally diverse proteins; however, they are limited in their ability to accurately represent electrostatic interactions. Here we have experimentally tested the role of charged residues on stability and folding kinetics of one of the most widely simulated β-proteins, the WW domain. The folding of wild type Pin1 WW domain, which has two positively charged residues in the first turn, was compared to the fast folding mutant FiP35 Pin1, which introduces a negative charge into the first turn. A combination of FTIR spectroscopy and laser-induced temperature-jump coupled with infrared spectroscopy was used to probe changes in the amide I region. The relaxation dynamics of the peptide backbone, β-sheets and β-turns, and negatively charged aspartic acid side chain of FiP35 were measured independently by probing the corresponding bands assigned in the amide I region. Folding is initiated in the turns and the β-sheets form last. While the global folding mechanism is in good agreement with simulation predictions, we observe changes in the protonation state of aspartic acid during folding that have not been captured by simulation methods. The protonation state of aspartic acid is coupled to protein folding; the apparent pKa of aspartic acid in the folded protein is 6.4. The dynamics of the aspartic acid follow the dynamics of the intermediate phase, supporting assignment of this phase to formation of the first hairpin. These results demonstrate the importance of electrostatic interactions in turn stability and formation of extended β-sheet structures.
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Affiliation(s)
- Caitlin M Davis
- Department of Chemistry, Emory University , Atlanta, Georgia 30322, United States
| | - R Brian Dyer
- Department of Chemistry, Emory University , Atlanta, Georgia 30322, United States
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14
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Sauer RT. Mutagenic dissection of the sequence determinants of protein folding, recognition, and machine function. Protein Sci 2013; 22:1675-87. [PMID: 23963737 DOI: 10.1002/pro.2334] [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: 07/31/2013] [Accepted: 08/12/2013] [Indexed: 11/08/2022]
Abstract
Understanding the relationship between the amino-acid sequence of a protein and its ability to fold and to function is one of the major challenges of protein science. Here, cases are reviewed in which mutagenesis, biochemistry, structure determination, protein engineering, and single-molecule biophysics have illuminated the sequence determinants of folding, binding specificity, and biological function for DNA-binding proteins and ATP-fueled machines that forcibly unfold native proteins as a prelude to degradation. In addition to structure-function relationships, these studies provide information about folding intermediates, mutations that accelerate folding, slow unfolding, and stabilize proteins against denaturation, show how new binding specificities and folds can evolve, and reveal strategies that proteolytic machines use to recognize, unfold, and degrade thousands of distinct substrates.
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Affiliation(s)
- Robert T Sauer
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139
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15
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Schlebach JP, Peng D, Kroncke BM, Mittendorf KF, Narayan M, Carter BD, Sanders CR. Reversible folding of human peripheral myelin protein 22, a tetraspan membrane protein. Biochemistry 2013; 52:3229-41. [PMID: 23639031 DOI: 10.1021/bi301635f] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Misfolding of the α-helical membrane protein peripheral myelin protein 22 (PMP22) has been implicated in the pathogenesis of the common neurodegenerative disease known as Charcot-Marie-Tooth disease (CMTD) and also several other related peripheral neuropathies. Emerging evidence suggests that the propensity of PMP22 to misfold in the cell may be due to an intrinsic lack of conformational stability. Therefore, quantitative studies of the conformational equilibrium of PMP22 are needed to gain insight into the molecular basis of CMTD. In this work, we have investigated the folding and unfolding of wild type (WT) human PMP22 in mixed micelles. Both kinetic and thermodynamic measurements demonstrate that the denaturation of PMP22 by n-lauroyl sarcosine (LS) in dodecylphosphocholine (DPC) micelles is reversible. Assessment of the conformational equilibrium indicates that a significant fraction of unfolded PMP22 persists even in the absence of the denaturing detergent. However, we find the stability of PMP22 is increased by glycerol, which facilitates quantitation of thermodynamic parameters. To our knowledge, this work represents the first report of reversible unfolding of a eukaryotic multispan membrane protein. The results indicate that WT PMP22 possesses minimal conformational stability in micelles, which parallels its poor folding efficiency in the endoplasmic reticulum. Folding equilibrium measurements for PMP22 in micelles may provide an approach to assess the effects of cellular metabolites or potential therapeutic agents on its stability. Furthermore, these results pave the way for future investigation of the effects of pathogenic mutations on the conformational equilibrium of PMP22.
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Affiliation(s)
- Jonathan P Schlebach
- Department of Biochemistry and ‡Center for Structural Biology, Vanderbilt University School of Medicine , Nashville, Tennessee 37232, United States
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16
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Aioanei D, Brucale M, Tessari I, Bubacco L, Samorì B. Worm-like Ising model for protein mechanical unfolding under the effect of osmolytes. Biophys J 2012; 102:342-50. [PMID: 22339871 PMCID: PMC3260691 DOI: 10.1016/j.bpj.2011.12.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Revised: 10/12/2011] [Accepted: 12/06/2011] [Indexed: 10/14/2022] Open
Abstract
We show via single-molecule mechanical unfolding experiments that the osmolyte glycerol stabilizes the native state of the human cardiac I27 titin module against unfolding without shifting its unfolding transition state on the mechanical reaction coordinate. Taken together with similar findings on the immunoglobulin-binding domain of streptococcal protein G (GB1), these experimental results suggest that osmolytes act on proteins through a common mechanism that does not entail a shift of their unfolding transition state. We investigate the above common mechanism via an Ising-like model for protein mechanical unfolding that adds worm-like-chain behavior to a recent generalization of the Wako-Saitô-Muñoz-Eaton model with support for group-transfer free energies. The thermodynamics of the model are exactly solvable, while protein kinetics under mechanical tension can be simulated via Monte Carlo algorithms. Notably, our force-clamp and velocity-clamp simulations exhibit no shift in the position of the unfolding transition state of GB1 and I27 under the effect of various osmolytes. The excellent agreement between experiment and simulation strongly suggests that osmolytes do not assume a structural role at the mechanical unfolding transition state of proteins, acting instead by adjusting the solvent quality for the protein chain analyte.
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Affiliation(s)
- Daniel Aioanei
- Department of Biochemistry G. Moruzzi, University of Bologna, Bologna, Italy.
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Kiefhaber T, Bachmann A, Jensen KS. Dynamics and mechanisms of coupled protein folding and binding reactions. Curr Opin Struct Biol 2011; 22:21-9. [PMID: 22129832 DOI: 10.1016/j.sbi.2011.09.010] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Accepted: 09/27/2011] [Indexed: 11/28/2022]
Abstract
Protein folding coupled to binding of a specific ligand is frequently observed in biological processes. In recent years numerous studies have addressed the structural properties of the unfolded proteins in the absence of their ligands. Surprisingly few time-resolved investigations on coupled folding and binding reactions have been published up to date and the dynamics and kinetic mechanisms of these processes are still only poorly understood. Especially, it is still unsolved for most systems which conformation of the protein is recognized by the ligand (conformational selection vs. folding-after-binding) and whether the ligand influences the folding kinetics. Here we review experimental methods, kinetic models and time-resolved experimental studies of coupled folding and binding reactions.
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Affiliation(s)
- Thomas Kiefhaber
- Munich Center for Integrated Protein Science at the Chemistry Department, TU München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
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18
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Probing dimer interface stabilization within a four-helix bundle of the GrpE protein from Escherichia coli via internal deletion mutants: conversion of a dimer to monomer. Int J Biol Macromol 2011; 48:627-33. [PMID: 21315107 DOI: 10.1016/j.ijbiomac.2011.02.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2010] [Revised: 01/31/2011] [Accepted: 02/02/2011] [Indexed: 11/23/2022]
Abstract
Insight into protein stability and folding remains an important area for protein research, in particular protein-protein interactions and the self-assembly of homodimers. The GrpE protein from Escherichia coli is a homodimer with a four-helix bundle at the dimer interface. Each monomer contributes a helix-loop-helix to the bundle. To probe the interface stabilization requirements, in terms of the amount of buried residues in the bundle necessary for dimer formation, internal deletion mutants (IDMs) were created that sequentially truncate each of the two helices in the helix-loop-helix region. Circular dichroism (CD) spectroscopy showed that all IDM's still contained a significant amount of α-helical secondary structure. IDM's that contained 11 or fewer of 22 residues originally present in the helices, or those that lost at least 50% of residues with less than 20% the solvent accessible surfaces (that is, hydrophobic residues) were unable to form a significant amount of dimer species as shown by chemical cross-linking. Gel filtration studies of IDM3.0 (one that retains 10 residues in each helix) show this variant to be mainly monomeric.
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19
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Knott BC, Duff N, Doherty MF, Peters B. Estimating diffusivity along a reaction coordinate in the high friction limit: Insights on pulse times in laser-induced nucleation. J Chem Phys 2009; 131:224112. [DOI: 10.1063/1.3268704] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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20
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Fernandez-Lafuente R. Stabilization of multimeric enzymes: Strategies to prevent subunit dissociation. Enzyme Microb Technol 2009. [DOI: 10.1016/j.enzmictec.2009.08.009] [Citation(s) in RCA: 503] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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21
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Moreau KL, King J. Hydrophobic core mutations associated with cataract development in mice destabilize human gammaD-crystallin. J Biol Chem 2009; 284:33285-95. [PMID: 19758984 PMCID: PMC2785171 DOI: 10.1074/jbc.m109.031344] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The human eye lens is composed of fiber cells packed with crystallins up to 450 mg/ml. Human γD-crystallin (HγD-Crys) is a monomeric, two-domain protein of the lens central nucleus. Both domains of this long lived protein have double Greek key β-sheet folds with well packed hydrophobic cores. Three mutations resulting in amino acid substitutions in the γ-crystallin buried cores (two in the N-terminal domain (N-td) and one in the C-terminal domain (C-td)) cause early onset cataract in mice, presumably an aggregated state of the mutant crystallins. It has not been possible to identify the aggregating precursor within lens tissues. To compare in vivo cataract-forming phenotypes with in vitro unfolding and aggregation of γ-crystallins, mouse mutant substitutions were introduced into HγD-Crys. The mutant proteins L5S, V75D, and I90F were expressed and purified from Escherichia coli. WT HγD-Crys unfolds in vitro through a three-state pathway, exhibiting an intermediate with the N-td unfolded and the C-td native-like. L5S and V75D in the N-td also displayed three-state unfolding transitions, with the first transition, unfolding of the N-td, shifted to significantly lower denaturant concentrations. I90F destabilized the C-td, shifting the overall unfolding transition to lower denaturant concentrations. During thermal denaturation, the mutant proteins exhibited lowered thermal stability compared with WT. Kinetic unfolding experiments showed that the N-tds of L5S and V75D unfolded faster than WT. I90F was globally destabilized and unfolded more rapidly. These results support models of cataract formation in which generation of partially unfolded species are precursors to the aggregated cataractous states responsible for light scattering.
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Affiliation(s)
- Kate L Moreau
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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22
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Confinement effects on the kinetics and thermodynamics of protein dimerization. Proc Natl Acad Sci U S A 2009; 106:5517-22. [PMID: 19297622 DOI: 10.1073/pnas.0809649106] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In the cell, protein complexes form by relying on specific interactions between their monomers. Excluded volume effects due to molecular crowding would lead to correlations between molecules even without specific interactions. What is the interplay of these effects in the crowded cellular environment? We study dimerization of a model homodimer when the mondimers are free and when they are tethered to each other. We consider a structured environment: Two monomers first diffuse into a cavity of size L and then fold and bind within the cavity. The folding and binding are simulated by using molecular dynamics based on a simplified topology based model. The confinement in the cell is described by an effective molecular concentration C approximately L(-3). A two-state coupled folding and binding behavior is found. We show the maximal rate of dimerization occurred at an effective molecular concentration C(op) approximately = 1 mM, which is a relevant cellular concentration. In contrast, for tethered chains the rate keeps at a plateau when C < C(op) but then decreases sharply when C > C(op). For both the free and tethered cases, the simulated variation of the rate of dimerization and thermodynamic stability with effective molecular concentration agrees well with experimental observations. In addition, a theoretical argument for the effects of confinement on dimerization is also made.
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23
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Rumfeldt JAO, Galvagnion C, Vassall KA, Meiering EM. Conformational stability and folding mechanisms of dimeric proteins. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 98:61-84. [PMID: 18602415 DOI: 10.1016/j.pbiomolbio.2008.05.004] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The folding of multisubunit proteins is of tremendous biological significance since the large majority of proteins exist as protein-protein complexes. Extensive experimental and computational studies have provided fundamental insights into the principles of folding of small monomeric proteins. Recently, important advances have been made in extending folding studies to multisubunit proteins, in particular homodimeric proteins. This review summarizes the equilibrium and kinetic theory and models underlying the quantitative analysis of dimeric protein folding using chemical denaturation, as well as the experimental results that have been obtained. Although various principles identified for monomer folding also apply to the folding of dimeric proteins, the effects of subunit association can manifest in complex ways, and are frequently overlooked. Changes in molecularity typically give rise to very different overall folding behaviour than is observed for monomeric proteins. The results obtained for dimers have provided key insights pertinent to understanding biological assembly and regulation of multisubunit proteins. These advances have set the stage for future advances in folding involving protein-protein interactions for natural multisubunit proteins and unnatural assemblies involved in disease.
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Affiliation(s)
- Jessica A O Rumfeldt
- Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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24
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Peimbert M, Domínguez-Ramírez L, Fernández-Velasco DA. Hydrophobic Repacking of the Dimer Interface of Triosephosphate Isomerase by in Silico Design and Directed Evolution. Biochemistry 2008; 47:5556-64. [DOI: 10.1021/bi702502k] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Mariana Peimbert
- Laboratorio de Fisicoquímica e Ingeniería de Proteínas, Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 México, DF, Mexico
| | - Lenin Domínguez-Ramírez
- Laboratorio de Fisicoquímica e Ingeniería de Proteínas, Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 México, DF, Mexico
| | - D. Alejandro Fernández-Velasco
- Laboratorio de Fisicoquímica e Ingeniería de Proteínas, Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Apdo. Postal 70-159, 04510 México, DF, Mexico
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25
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Du D, Bunagan MR, Gai F. The effect of charge-charge interactions on the kinetics of alpha-helix formation. Biophys J 2007; 93:4076-82. [PMID: 17704172 PMCID: PMC2084238 DOI: 10.1529/biophysj.107.108548] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The formation of the monomeric alpha-helix represents one of the simplest scenarios in protein folding; however, our current understanding of the folding dynamics of the alpha-helix motif is mainly based on studies of alanine-rich model peptides. To examine the effect of peptide sequence on the folding kinetics of alpha-helices, we studied the relaxation kinetics of a 21-residue helical peptide, Conantokin-T (Con-T), using time-resolved infrared spectroscopy in conjunction with a laser-induced temperature jump technique. Con-T is a neuroactive peptide containing a large number of charged residues that is found in the venom of the piscivorous cone snail Conus tulipa . The temperature-jump relaxation kinetics of Con-T is distinctly slower than that of previously studied alanine-based peptides, suggesting that the folding time of alpha-helices is sequence-dependent. Furthermore, it appears that the slower folding of Con-T can be attributed to the fact that its helical conformation is stabilized by charge-charge interactions or salt bridges. Although this finding contradicts an earlier molecular dynamics simulation, it also has implications for existing models of protein folding.
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Affiliation(s)
- Deguo Du
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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26
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Nájera H, Dagdug L, Fernández-Velasco DA. Thermodynamic and kinetic characterization of the association of triosephosphate isomerase: the role of diffusion. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2007; 1774:985-94. [PMID: 17644053 DOI: 10.1016/j.bbapap.2007.06.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2007] [Revised: 05/26/2007] [Accepted: 06/13/2007] [Indexed: 12/12/2022]
Abstract
It is known that diffusion plays a central role in the folding of small monomeric proteins and in the rigid-body association of proteins, however, the role of diffusion in the association of the folding intermediates of oligomeric proteins has been scarcely explored. In this work, catalytic activity and fluorescence measurements were used to study the effect of viscosity in the unfolding and refolding of the homodimeric enzyme triosephosphate isomerase from Saccharamyces cerevisiae. Two transitions were found by equilibrium and kinetic experiments, suggesting a three-state model with a monomeric intermediate. Glycerol barely affects DeltaG(0)(fold) whereas DeltaG(0)(assoc) becomes more favourable in the presence of the cosolvent. From 0 to 60% (v/v) glycerol, the association rate constant showed a near unitary dependence on solvent viscosity. However, at higher glycerol concentrations deviations from Kramers theory were observed. The dissociation rate constant showed a viscosity effect much higher than one. This may be related to secondary effects such as short-range glycerol-induced repulsion between monomers. Nevertheless, after comparison under isostability conditions, a slope near one was also observed for the dissociation rate. These results strongly suggest that the bimolecular association producing the native dimer is limited by diffusional events of the polypeptide chains through the solvent.
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Affiliation(s)
- Hugo Nájera
- Area Académica de Nutrición, Instituto de Ciencias de la Salud, Universidad Autónoma del Estado de Hidalgo, Pachuca, Hidalgo, México.
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27
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Pradeep L, Udgaonkar JB. Diffusional Barrier in the Unfolding of a Small Protein. J Mol Biol 2007; 366:1016-28. [PMID: 17188296 DOI: 10.1016/j.jmb.2006.11.064] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Revised: 10/26/2006] [Accepted: 11/22/2006] [Indexed: 10/23/2022]
Abstract
To determine how the dynamics of the polypeptide chain in a protein molecule are coupled to the bulk solvent viscosity, the unfolding by urea of the small protein barstar was studied in the presence of two viscogens, xylose and glycerol. Thermodynamic studies of unfolding show that both viscogens stabilize barstar by a preferential hydration mechanism, and that viscogen and urea act independently on protein stability. Kinetic studies of unfolding show that while the rate-limiting conformational change during unfolding is dependent on the bulk solvent viscosity, eta, its rate does not show an inverse dependence on eta, as expected by Kramers' theory. Instead, the rate is found to be inversely proportional to an effective viscosity, eta + xi, where xi is an adjustable parameter which needs to be included in the rate equation. xi is found to have a value of -0.7 cP in xylose and -0.5 cP in glycerol, in the case of unfolding, at constant urea concentration as well as under isostability conditions. Hence, the unfolding protein chain does not experience the bulk solvent viscosity, but instead an effective solvent viscosity, which is lower than the bulk solvent viscosity by either 0.7 cP or 0.5 cP. A second important result is the validation of the isostability assumption, commonly used in protein folding studies but hitherto untested, according to which if a certain concentration of urea can nullify the effect of a certain concentration of viscogen on stability, then the same concentrations of urea and viscogen will also not perturb the free energy of activation of the unfolding of the protein.
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Affiliation(s)
- Lovy Pradeep
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, GKVK Campus, Bangalore, India
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28
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Park S, Saven JG. Statistical and molecular dynamics studies of buried waters in globular proteins. Proteins 2006; 60:450-63. [PMID: 15937899 DOI: 10.1002/prot.20511] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Buried solvent molecules are common in the core of globular proteins and contribute to structural stability. Folding necessitates the burial of polar backbone atoms in the protein core, whose hydrogen-bonding capacities should be satisfied on average. Whereas the residues in alpha-helices and beta-sheets form systematic main-chain hydrogen bonds, the residues in turns, coils and loops often contain polar atoms that fail to form intramolecular hydrogen bonds. The statistical analysis of 842 high resolution protein structures shows that well-resolved, internal water molecules preferentially reside near residues without alpha-helical and beta-sheet secondary structures. These buried waters most often form primary hydrogen bonds to main-chain atoms not involved in intramolecular hydrogen bonds, providing strong evidence that hydrating main-chain atoms is a key structural role of buried water molecules. Additionally, the average B-factor of protein atoms hydrogen-bonded to waters is smaller than that of protein atoms forming intramolecular hydrogen bonds, and the average B-factor of water molecules involved in primary hydrogen bonds with main-chain atoms is smaller than the average B-factor of water molecules involved in secondary hydrogen bonds to protein atoms that form concurrent intramolecular hydrogen bonds. To study the structural coupling between internal waters and buried polar atoms in detail we simulated the dynamics of wild-type FKBP12, in which a buried water, Wat137, forms one side-chain and multiple main-chain hydrogen bonds. We mutated E60, whose side-chain hydrogen bonds with Wat137, to Q, N, S or A, to modulate the multiplicity and geometry of hydrogen bonds to the water. Mutating E60 to a residue that is unable to form a hydrogen bond with Wat137 results in reorientation of the water molecule and leads to a structural readjustment of residues that are both near and distant to the water. We predict that the E60A mutation will result in a significantly reduced affinity of FKBP12 for its ligand FK506. The propensity of internal waters to hydrogen bond to buried polar atoms suggests that ordered water molecules may constitute fundamental structural components of proteins, particularly in regions where alpha-helical or beta-sheet secondary structure is not present.
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Affiliation(s)
- Sheldon Park
- Makineni Theoretical Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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29
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Geney R, Layten M, Gomperts R, Hornak V, Simmerling C. Investigation of Salt Bridge Stability in a Generalized Born Solvent Model. J Chem Theory Comput 2005; 2:115-27. [DOI: 10.1021/ct050183l] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Raphaël Geney
- Department of Chemistry, Graduate Program in Molecular and Cellular Biology, and Center for Structural Biology, Stony Brook University, Stony Brook, New York 11794-3400, and Silicon Graphics Inc., Applications Engineering Group, Hudson, Massachusetts 01749
| | - Melinda Layten
- Department of Chemistry, Graduate Program in Molecular and Cellular Biology, and Center for Structural Biology, Stony Brook University, Stony Brook, New York 11794-3400, and Silicon Graphics Inc., Applications Engineering Group, Hudson, Massachusetts 01749
| | - Roberto Gomperts
- Department of Chemistry, Graduate Program in Molecular and Cellular Biology, and Center for Structural Biology, Stony Brook University, Stony Brook, New York 11794-3400, and Silicon Graphics Inc., Applications Engineering Group, Hudson, Massachusetts 01749
| | - Viktor Hornak
- Department of Chemistry, Graduate Program in Molecular and Cellular Biology, and Center for Structural Biology, Stony Brook University, Stony Brook, New York 11794-3400, and Silicon Graphics Inc., Applications Engineering Group, Hudson, Massachusetts 01749
| | - Carlos Simmerling
- Department of Chemistry, Graduate Program in Molecular and Cellular Biology, and Center for Structural Biology, Stony Brook University, Stony Brook, New York 11794-3400, and Silicon Graphics Inc., Applications Engineering Group, Hudson, Massachusetts 01749
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30
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de Prat-Gay G, Nadra AD, Corrales-Izquierdo FJ, Alonso LG, Ferreiro DU, Mok YK. The Folding Mechanism of a Dimeric β-Barrel Domain. J Mol Biol 2005; 351:672-82. [PMID: 16023675 DOI: 10.1016/j.jmb.2005.05.070] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2005] [Revised: 05/10/2005] [Accepted: 05/31/2005] [Indexed: 10/25/2022]
Abstract
The dimeric beta-barrel domain is an unusual topology, shared only by two viral origin binding proteins, where secondary, tertiary and quaternary structure are coupled, and where the dimerization interface is composed of two four-stranded half-beta-barrels. The folding of the DNA binding domain of the E2 transcriptional regulator from human papillomavirus, strain-16, takes place through a stable and compact monomeric intermediate, with 31% the stability of the folded dimeric domain. Double jump multiple wavelength experiments allowed the reconstruction of the fluorescence spectrum of the monomeric intermediate at 100 milliseconds, indicating that tryptophan residues, otherwise buried in the folded state, are accessible to the solvent. Burial of surface area as well as differential behavior to ionic strength and pH with respect to the native ground state, plus the impossibility of having over 2500 A2 of surface area of the half-barrel exposed to the solvent, indicates that the formation of a non-native compact tertiary structure precedes the assembly of native quaternary structure. The monomeric intermediate can dimerize, albeit with a weaker affinity (approximately 1 microM), to yield a non-native dimeric intermediate, which rearranges to the native dimer through a parallel folding channel, with a unimolecular rate-limiting step. Folding pathways from either acid or urea unfolded states are identical, making the folding model robust. Unfolding takes place through a major phase accounting for apparently all the secondary structure change, with identical rate constant to that of the fluorescence unfolding experiment. In contrast to the folding direction, no unfolding intermediate was found.
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Affiliation(s)
- Gonzalo de Prat-Gay
- Instituto Leloir, CONICET, and Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Patricias Argentinas 435, (1405) Buenos Aires, Argentina.
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31
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Abstract
The structure and folding mechanism of a given protein are determined by many factors, including the electrostatic interactions between charged residues of protein molecules known in general as salt bridges. In this study, analyses were conducted on 10,370 salt bridges in 2017 proteins and the results compared to previous statistical surveys of 36 protein structures. Although many of the general trends remained consistent with other studies, more detailed information was illuminated by the larger dataset. In particular, it was shown that there is a strong correlation between secondary structure and salt bridge formation, and that salt bridges display preferential formation in an environment of about 30% solvent accessible surface area.
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Affiliation(s)
- James N Sarakatsannis
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, USA
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32
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Brown C, Liao J, Wittung-Stafshede P. Interface mutation in heptameric co-chaperonin protein 10 destabilizes subunits but not interfaces. Arch Biochem Biophys 2005; 439:175-83. [PMID: 15978542 DOI: 10.1016/j.abb.2005.05.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2005] [Revised: 05/11/2005] [Accepted: 05/13/2005] [Indexed: 11/22/2022]
Abstract
We here report on a human mitochondrial co-chaperonin protein 10 (cpn10) variant in which the conserved interface residue leucine-96 is replaced with glycine (Leu96Gly cpn10). According to analytical ultracentrifugation, the mutation does not perturb the ability to assemble into a heptamer and electron microscopy reveals that Leu96Gly cpn10 is ring-shaped like wild-type cpn10. Despite elimination of a hydrophobic residue, the subunit-subunit affinity is essentially identical in Leu96Gly cpn10 and in wild-type cpn10. This is explained by a compensating rearrangement in Leu96Gly cpn10, evident from cross-linking and gel-filtration experiments. As a direct result of lower monomer stability, Leu96Gly cpn10 is dramatically less stable towards chemical and thermal perturbations as compared to wild-type cpn10. We conclude that leucine-96 is an interface residue preserved to guarantee stable cpn10 monomers. Our study demonstrates that the cpn10 interfaces can adapt to structural alterations without loss of either subunit-subunit affinity or heptamer specificity.
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Affiliation(s)
- Christopher Brown
- Department of Biochemistry and Cell Biology, Rice University, Houston, TX 77251, USA
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33
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Huang F, Hudgins RR, Nau WM. Primary and secondary structure dependence of peptide flexibility assessed by fluorescence-based measurement of end-to-end collision rates. J Am Chem Soc 2005; 126:16665-75. [PMID: 15600373 DOI: 10.1021/ja0466053] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The intrachain fluorescence quenching of the fluorophore 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) is measured in short peptide fragments, namely the two strands and the turn of the N-terminal beta-hairpin of ubiquitin. The investigated peptides adopt a random-coil conformation in aqueous solution according to CD and NMR experiments. The combination of quenchers with different quenching efficiencies, namely tryptophan and tyrosine, allows the extrapolation of the rate constants for end-to-end collision rates as well as the dissociation of the end-to-end encounter complex. The measured activation energies for fluorescence quenching demonstrate that the end-to-end collision process in peptides is partially controlled by internal friction within the backbone, while measurements in solvents of different viscosities (H2O, D2O, and 7.0 M guanidinium chloride) suggest that solvent friction is an additional important factor in determining the collision rate. The extrapolated end-to-end collision rates, which are only slightly larger than the experimental rates for the DBO/Trp probe/quencher system, provide a measure of the conformational flexibility of the peptide backbone. The chain flexibility is found to be strongly dependent on the type of secondary structure that the peptides represent. The collision rates for peptides derived from the beta-strand motifs (ca. 1 x 10(7) s(-1)) are ca. 4 times slower than that derived from the beta-turn. The results provide further support for the hypothesis that chain flexibility is an important factor in the preorganization of protein fragments during protein folding. Mutations to the beta-turn peptide show that subtle sequence changes strongly affect the flexibility of peptides as well. The protonation and charge status of the peptides, however, are shown to have no significant effect on the flexibility of the investigated peptides. The meaning and definition of end-to-end collision rates in the context of protein folding are critically discussed.
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Affiliation(s)
- Fang Huang
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland
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34
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Middaugh CR, Edwards KL. Recent advances in our understanding of protein conformational stability from a pharmaceutical perspective. Expert Opin Investig Drugs 2005; 7:1493-500. [PMID: 15992046 DOI: 10.1517/13543784.7.9.1493] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The marginal conformational stability of proteins has made them in some cases less than ideal candidates for pharmaceutical agents. Recent progress in our understanding of protein structure and stability has provided the opportunity to design the desired degree of stability into protein drug candidates. Modifications such as the optimisation of interior side-chain packing, the introduction of new ion-pairs, as well as the design of stabilising disulfide bridges and ligand binding sites, all offer the opportunity to produce proteins with enhanced stability properties.
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Affiliation(s)
- C R Middaugh
- Department of Pharmaceutical Chemistry, University of Kansas, 2095 Constant Avenue, Lawrence, KS 66047, USA
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35
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Drury J, Narayanaswami V. Examination of lipid-bound conformation of apolipoprotein E4 by pyrene excimer fluorescence. J Biol Chem 2005; 280:14605-10. [PMID: 15708851 DOI: 10.1074/jbc.m414019200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Apolipoprotein E (apoE) is a 34-kDa resident of lipoproteins that plays a key role in cholesterol homeostasis in plasma and in brain. It is composed of an N-terminal (NT) domain (residues 1-191) and a C-terminal (CT) domain (residues 201-299). Of the three major isoforms (apoE2, -E3, and -E4), apoE4 is considered a risk factor for both cardiovascular and Alzheimer disease. Compared with apoE3, domain interaction between NT and CT domains is believed to direct the lipoprotein distribution preference of apoE4 for very low density lipoprotein-sized particles. We examined the relative disposition of apoE4 NT and CT domains in lipid-free and lipid-bound forms by monitoring pyrene excimer fluorescence emission as a direct indicator of spatial proximity. Site-specific labeling of apoE4 by N-(1-pyrene)maleimide was accomplished after substitution of Cys residues for Arg-61 in NT domain and Glu-255 in CT domain. Pyrene labeling did not alter the lipoprotein distribution pattern of apoE4 in plasma. Pyrene excimer fluorescence was noted in lipid-free pyrene-R61C/E255C/apoE4 in mixtures containing excess wild-type apoE4, which was attributed to intramolecular spatial proximity between these specified sites. Upon disruption of tertiary interaction, a large decrease in excimer fluorescence emission was noted in pyrene-R61C/E255C/apoE4. In dimyristoylphosphatidylcholine/pyrene-R61C/E255C/apoE4 discoidal complexes, pyrene excimer fluorescence emission was retained. Taken together with fluorescence quenching and cross-linking analysis, a looped-back model of apoE4 is proposed in lipid-bound state, including spherical lipoprotein particles, wherein residues Arg-61 and Glu-255 are proximal to one another.
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Affiliation(s)
- Jessica Drury
- Lipid Biology in Health and Disease Research Group, Children's Hospital Oakland Research Institute, Oakland, California 94609, USA
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Forrer P, Chang C, Ott D, Wlodawer A, Plückthun A. Kinetic stability and crystal structure of the viral capsid protein SHP. J Mol Biol 2004; 344:179-93. [PMID: 15504410 DOI: 10.1016/j.jmb.2004.09.030] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2004] [Revised: 09/09/2004] [Accepted: 09/15/2004] [Indexed: 10/26/2022]
Abstract
SHP, the capsid-stabilizing protein of lambdoid phage 21, is highly resistant against denaturant-induced unfolding. We demonstrate that this high functional stability of SHP is due to a high kinetic stability with a half-life for unfolding of 25 days at zero denaturant, while the thermodynamic stability is not unusually high. Unfolding experiments demonstrated that the trimeric state (also observed in crystals and present on the phage capsid) of SHP is kinetically stable in solution, while the monomer intermediate unfolds very rapidly. We also determined the crystal structure of trimeric SHP at 1.5A resolution, which was compared to that of its functional homolog gpD. This explains how a tight network of H-bonds rigidifies crucial interpenetrating residues, leading to the observed extremely slow trimer dissociation or denaturation. Taken as a whole, our results provide molecular-level insights into natural strategies to achieve kinetic stability by taking advantage of protein oligomerization. Kinetic stability may be especially needed in phage capsids to allow survival in harsh environments.
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Affiliation(s)
- Patrik Forrer
- Biochemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
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Zhu Y, Fu X, Wang T, Tamura A, Takada S, Saven JG, Gai F. Guiding the search for a protein's maximum rate of folding. Chem Phys 2004. [DOI: 10.1016/j.chemphys.2004.05.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Esteban O, Zhao H. Directed evolution of soluble single-chain human class II MHC molecules. J Mol Biol 2004; 340:81-95. [PMID: 15184024 DOI: 10.1016/j.jmb.2004.04.054] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2004] [Revised: 04/16/2004] [Accepted: 04/20/2004] [Indexed: 11/17/2022]
Abstract
Major histocompatibility complex (MHC) class II molecules are membrane-anchored heterodimers that present antigenic peptides to T cells. Expression of these molecules in soluble form has met limited success, presumably due to their large size, heterodimeric structure and the presence of multiple disulfide bonds. Here we have used directed evolution and yeast surface display to engineer soluble single-chain human lymphocyte antigen (HLA) class II MHC DR1 molecules without covalently attached peptides (scDR1alphabeta). Specifically, a library of mutant scDR1alphabeta molecules was generated by random mutagenesis and screened by fluorescence activated cell sorting (FACS) with DR-specific conformation-sensitive antibodies, yielding three well-expressed and properly folded scDR1alphabeta variants displayed on the yeast cell surface. Detailed analysis of these evolved variants and a few site-directed mutants generated de novo indicated three amino acid residues in the beta1 domain are important for the improved protein folding yield. Further, molecular modeling studies suggested these mutations might increase the protein folding efficiency by improving the packing of a hydrophobic core in the alpha1beta1 domain of DR1. The scDR1alphabeta mutants displayed on the yeast cell surface are remarkably stable and bind specifically to DR-specific peptide HA(306-318) with high sensitivity and rapid kinetics in flow cytometric assays. Moreover, since the expression, stability and peptide-binding properties of these mutants can be directly assayed on the yeast cell surface using immuno-fluorescence labeling and flow cytometry, time-consuming purification and refolding steps of recombinant DR1 molecules are eliminated. Therefore, these scDR1alphabeta molecules will provide a powerful technology platform for further design of DR1 molecules with improved peptide-binding specificity and affinity for therapeutic and diagnostic applications. The methods described here should be generally applicable to other class II MHC molecules and also class I MHC molecules for their functional expression, characterization and engineering.
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Affiliation(s)
- Olga Esteban
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 S. Mathews Ave, Urbana, IL 61801, USA
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39
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Bergasa-Caceres F, Rabitz HA. Sequential Collapse Folding Pathway of Staphylococcal Nuclease: Entropic Activation Barriers to Hydrophobic Collapse of the Protein Core. J Phys Chem B 2004. [DOI: 10.1021/jp031023d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | - Herschel A. Rabitz
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544
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40
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Abstract
Small monomeric proteins often fold in apparent two-state processes with folding speeds dictated by their native-state topology. Here we test, for the first time, the influence of monomer topology on the folding speed of an oligomeric protein: the heptameric cochaperonin protein 10 (cpn10), which in the native state has seven beta-barrel subunits noncovalently assembled through beta-strand pairing. Cpn10 is a particularly useful model because equilibrium-unfolding experiments have revealed that the denatured state in urea is that of a nonnative heptamer. Surprisingly, refolding of the nonnative cpn10 heptamer is a simple two-state kinetic process with a folding-rate constant in water (2.1 sec(-1); pH 7.0, 20 degrees C) that is in excellent agreement with the prediction based on the native-state topology of the cpn10 monomer. Thus, the monomers appear to fold as independent units, with a speed that correlates with topology, although the C and N termini are trapped in beta-strand pairing with neighboring subunits. In contrast, refolding of unfolded cpn10 monomers is dominated by a slow association step.
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Affiliation(s)
- Neil Bascos
- Molecular and Cellular Biology Graduate Program, Tulane University, New Orleans, Louisiana 70112, USA
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41
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Güthe S, Kapinos L, Möglich A, Meier S, Grzesiek S, Kiefhaber T. Very Fast Folding and Association of a Trimerization Domain from Bacteriophage T4 Fibritin. J Mol Biol 2004; 337:905-15. [PMID: 15033360 DOI: 10.1016/j.jmb.2004.02.020] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2003] [Revised: 01/30/2004] [Accepted: 02/05/2004] [Indexed: 11/27/2022]
Abstract
The foldon domain constitutes the C-terminal 30 amino acid residues of the trimeric protein fibritin from bacteriophage T4. Its function is to promote folding and trimerization of fibritin. We investigated structure, stability and folding mechanism of the isolated foldon domain. The domain folds into the same trimeric beta-propeller structure as in fibritin and undergoes a two-state unfolding transition from folded trimer to unfolded monomers. The folding kinetics involve several consecutive reactions. Structure formation in the region of the single beta-hairpin of each monomer occurs on the submillisecond timescale. This reaction is followed by two consecutive association steps with rate constants of 1.9(+/-0.5)x10(6)M(-1)s(-1) and 5.4(+/-0.3)x10(6)M(-1)s(-1) at 0.58 M GdmCl, respectively. This is similar to the fastest reported bimolecular association reactions for folding of dimeric proteins. At low concentrations of protein, folding shows apparent third-order kinetics. At high concentrations of protein, the reaction becomes almost independent of protein concentrations with a half-time of about 3 ms, indicating that a first-order folding step from a partially folded trimer to the native protein (k=210 +/- 20 s(-1)) becomes rate-limiting. Our results suggest that all steps on the folding/trimerization pathway of the foldon domain are evolutionarily optimized for rapid and specific initiation of trimer formation during fibritin assembly. The results further show that beta-hairpins allow efficient and rapid protein-protein interactions during folding.
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Affiliation(s)
- Sarah Güthe
- Division of Biophysical Chemistry, Biozentrum der Universität Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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42
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Affiliation(s)
- Ting Wang
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Yongjin Zhu
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Feng Gai
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104
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43
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Gruia AD, Fischer S, Smith JC. Kinetics of breaking a salt-bridge critical in protein unfolding. Chem Phys Lett 2004. [DOI: 10.1016/j.cplett.2003.12.038] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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44
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Schäfer K, Magnusson U, Scheffel F, Schiefner A, Sandgren MOJ, Diederichs K, Welte W, Hülsmann A, Schneider E, Mowbray SL. X-ray structures of the maltose-maltodextrin-binding protein of the thermoacidophilic bacterium Alicyclobacillus acidocaldarius provide insight into acid stability of proteins. J Mol Biol 2004; 335:261-74. [PMID: 14659755 DOI: 10.1016/j.jmb.2003.10.042] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Maltose-binding proteins act as primary receptors in bacterial transport and chemotaxis systems. We report here crystal structures of the thermoacidostable maltose-binding protein from Alicyclobacillus acidocaldarius, and explore its modes of binding to maltose and maltotriose. Further, comparison with the structures of related proteins from Escherichia coli (a mesophile), and two hyperthermophiles (Pyrococcus furiosus and Thermococcus litoralis) allows an investigation of the basis of thermo- and acidostability in this family of proteins.The thermoacidophilic protein has fewer charged residues than the other three structures, which is compensated by an increase in the number of polar residues. Although the content of acidic and basic residues is approximately equal, more basic residues are exposed on its surface whereas most acidic residues are buried in the interior. As a consequence, this protein has a highly positive surface charge. Fewer salt bridges are buried than in the other MBP structures, but the number exposed on its surface does not appear to be unusual. These features appear to be correlated with the acidostability of the A. acidocaldarius protein rather than its thermostability. An analysis of cavities within the proteins shows that the extremophile proteins are more closely packed than the mesophilic one. Proline content is slightly higher in the hyperthermophiles and thermoacidophiles than in mesophiles, and this amino acid is more common at the second position of beta-turns, properties that are also probably related to thermostability. Secondary structural content does not vary greatly in the different structures, and so is not a contributing factor.
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Affiliation(s)
- Karsten Schäfer
- Fachbereich Biologie, Universität Konstanz, Universitätsstrasse 10, 78457, Konstanz, Germany
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45
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Zhu Y, Alonso DOV, Maki K, Huang CY, Lahr SJ, Daggett V, Roder H, DeGrado WF, Gai F. Ultrafast folding of alpha3D: a de novo designed three-helix bundle protein. Proc Natl Acad Sci U S A 2003; 100:15486-91. [PMID: 14671331 PMCID: PMC307594 DOI: 10.1073/pnas.2136623100] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Here, we describe the folding/unfolding kinetics of alpha3D, a small designed three-helix bundle. Both IR temperature jump and ultrafast fluorescence mixing methods reveal a single-exponential process consistent with a minimal folding time of 3.2 +/- 1.2 micros (at approximately 50 degrees C), indicating that a protein can fold on the 1- to 5-micros time scale. Furthermore, the single-exponential nature of the relaxation indicates that the prefactor for transition state (TS)-folding models is probably >or=1 (micros)-1 for a protein of this size and topology. Molecular dynamics simulations and IR spectroscopy provide a molecular rationale for the rapid, single-exponential folding of this protein. alpha3D shows a significant bias toward local helical structure in the thermally denatured state. The molecular dynamics-simulated TS ensemble is highly heterogeneous and dynamic, allowing access to the TS via multiple pathways.
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Affiliation(s)
- Yongjin Zhu
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA
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46
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Guidry JJ, Shewmaker F, Maskos K, Landry S, Wittung-Stafshede P. Probing the interface in a human co-chaperonin heptamer: residues disrupting oligomeric unfolded state identified. BMC BIOCHEMISTRY 2003; 4:14. [PMID: 14525625 PMCID: PMC270013 DOI: 10.1186/1471-2091-4-14] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/01/2003] [Accepted: 10/02/2003] [Indexed: 11/21/2022]
Abstract
Background The co-chaperonin protein 10 (cpn10) assists cpn60 in the folding of nonnative polypeptides in a wide range of organisms. All known cpn10 molecules are heptamers of seven identical subunits that are linked together by β-strand interactions at a large and flexible interface. Unfolding of human mitochondrial cpn10 in urea results in an unfolded heptameric state whereas GuHCl additions result in unfolded monomers. To address the role of specific interface residues in the assembly of cpn10 we prepared two point-mutated variants, in each case removing a hydrophobic residue positioned at the subunit-subunit interface. Results Replacing valine-100 with a glycine (Val100Gly cpn10) results in a wild-type-like protein with seven-fold symmetry although the thermodynamic stability is decreased and the unfolding processes in urea and GuHCl both result in unfolded monomers. In sharp contrast, replacing phenylalanine-8 with a glycine (Phe8Gly cpn10) results in a protein that has lost the ability to assemble. Instead, this protein exists mostly as unfolded monomers. Conclusions We conclude that valine-100 is a residue important to adopt an oligomeric unfolded state but it does not affect the ability to assemble in the folded state. In contrast, phenylalanine-8 is required for both heptamer assembly and monomer folding and therefore this mutation results in unfolded monomers at physiological conditions. Despite the plasticity and large size of the cpn10 interface, our observations show that isolated interface residues can be crucial for both the retention of a heptameric unfolded structure and for subunit folding.
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Affiliation(s)
- Jesse J Guidry
- Chemistry Department, Tulane University, New Orleans, 70118 Louisiana, USA
| | - Frank Shewmaker
- Chemistry Department, Tulane University, New Orleans, 70118 Louisiana, USA
| | - Karol Maskos
- Coordinated Instrumentation Facility, Tulane University, New Orleans, 70118 Louisiana, USA
| | - Samuel Landry
- Biochemistry Department, Tulane University, New Orleans, 70112 Louisiana, USA
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Zagrovic B, Pande V. Solvent viscosity dependence of the folding rate of a small protein: distributed computing study. J Comput Chem 2003; 24:1432-6. [PMID: 12868108 DOI: 10.1002/jcc.10297] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
By using distributed computing techniques and a supercluster of more than 20,000 processors we simulated folding of a 20-residue Trp Cage miniprotein in atomistic detail with implicit GB/SA solvent at a variety of solvent viscosities (gamma). This allowed us to analyze the dependence of folding rates on viscosity. In particular, we focused on the low-viscosity regime (values below the viscosity of water). In accordance with Kramers' theory, we observe approximately linear dependence of the folding rate on 1/gamma for values from 1-10(-1)x that of water viscosity. However, for the regime between 10(-4)-10(-1)x that of water viscosity we observe power-law dependence of the form k approximately gamma(-1/5). These results suggest that estimating folding rates from molecular simulations run at low viscosity under the assumption of linear dependence of rate on inverse viscosity may lead to erroneous results.
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Affiliation(s)
- Bojan Zagrovic
- Biophysics Program and Department of Chemistry, Stanford University, Stanford, CA 94305, USA
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48
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Relating contact order to the rate of cooperative collapse in the sequential collapse model for protein folding pathways. Chem Phys Lett 2003. [DOI: 10.1016/s0009-2614(03)01043-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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49
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Masunov A, Lazaridis T. Potentials of mean force between ionizable amino acid side chains in water. J Am Chem Soc 2003; 125:1722-30. [PMID: 12580597 DOI: 10.1021/ja025521w] [Citation(s) in RCA: 181] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Potentials of mean force (PMF) between all possible ionizable amino acid side chain pairs in various protonation states were calculated using explicit solvent molecular dynamics simulations with umbrella sampling and the weighted histogram analysis method. The side chains were constrained in various orientations inside a spherical cluster of 200 water molecules. Beglov and Roux's Spherical Solvent Boundary Potential was used to account for the solvent outside this sphere. This approach was first validated by calculating PMFs between monatomic ions (K(+), Na(+), Cl(-)) and comparing them to results from the literature and results obtained using Ewald summation. The strongest interaction (-4.5 kcal/mol) was found for the coaxial Arg(+).Glu(-) pair. Many like-charged side chains display a remarkable lack of repulsion, and occasionally a weak attraction. The PMFs are compared to effective energy curves obtained with common implicit solvation models, namely Generalized Born (GB), EEF1, and uniform dielectric of 80. Overall, the EEF1 curves are too attractive, whereas the GB curves in most cases match the minima of the PMF curves quite well. The uniform dielectric model, despite some fortuitous successes, is grossly inadequate.
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Affiliation(s)
- Artëm Masunov
- City College of the City University of New York, Convent Ave. at 138 St., New York, New York 10031, USA
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50
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Gruia AD, Fischer S, Smith JC. Molecular dynamics simulation reveals a surface salt bridge forming a kinetic trap in unfolding of truncated Staphylococcal nuclease. Proteins 2003; 50:507-15. [PMID: 12557192 DOI: 10.1002/prot.10312] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Surface salt bridges are ubiquitous in globular proteins. Their contribution to protein stability has been extensively debated in the past decade. Here, molecular dynamics simulations are performed starting from a non-equilibrium state of Staphylococcal nuclease (SNase) with C-terminal truncation (SNaseDelta). The results indicate a key role in the unfolding of the surface salt bridge between arginine 105 and glutamate 135. Experimentally, SNaseDelta is known to be partially unfolded. However, in simulations over 1 ns at 300 K and over 500 ps at 400 K, SNaseDelta remains stable in the native-like folded conformation, the salt bridge hindering unfolding. When the potential function is altered so as to selectively weaken the salt bridge, which then breaks rapidly at 430 K, the protein starts to unfold. The results suggest that breaking of this salt bridge presents a significant barrier to the unfolding transition of SNaseDelta from a native-like state to the unfolded state. Potential of mean force calculations indicate that the barrier height for this transition is approximately 7 kcal/mol.
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