1
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McDonnell RT, Elcock AH. AutoRNC: An automated modeling program for building atomic models of ribosome-nascent chain complexes. Structure 2024; 32:621-629.e5. [PMID: 38428431 PMCID: PMC11073581 DOI: 10.1016/j.str.2024.02.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 11/29/2023] [Accepted: 02/05/2024] [Indexed: 03/03/2024]
Abstract
The interpretation of experimental studies of co-translational protein folding often benefits from the use of computational methods that seek to model or simulate the nascent chain and its interactions with the ribosome. Building realistic 3D models of ribosome-nascent chain (RNC) constructs often requires expert knowledge, so to circumvent this issue, we describe here AutoRNC, an automated modeling program capable of constructing large numbers of plausible atomic models of RNCs within minutes. AutoRNC takes input from the user specifying any regions of the nascent chain that contain secondary or tertiary structure and attempts to build conformations compatible with those specifications-and with the constraints imposed by the ribosome-by sampling and progressively piecing together dipeptide conformations extracted from the Research Collaboratory for Structural Bioinformatics Protein Data Bank (RCSB). Despite using only modest computational resources, we show here that AutoRNC can build plausible conformations for a wide range of RNC constructs for which experimental data have already been reported.
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Affiliation(s)
- Robert T McDonnell
- Department of Biochemistry & Molecular Biology, University of Iowa, Iowa City, IA, USA
| | - Adrian H Elcock
- Department of Biochemistry & Molecular Biology, University of Iowa, Iowa City, IA, USA.
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2
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Baxa MC, Lin X, Mukinay CD, Chakravarthy S, Sachleben JR, Antilla S, Hartrampf N, Riback JA, Gagnon IA, Pentelute BL, Clark PL, Sosnick TR. How hydrophobicity, side chains, and salt affect the dimensions of disordered proteins. Protein Sci 2024; 33:e4986. [PMID: 38607226 PMCID: PMC11010952 DOI: 10.1002/pro.4986] [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: 10/23/2023] [Revised: 03/13/2024] [Accepted: 03/26/2024] [Indexed: 04/13/2024]
Abstract
Despite the generally accepted role of the hydrophobic effect as the driving force for folding, many intrinsically disordered proteins (IDPs), including those with hydrophobic content typical of foldable proteins, behave nearly as self-avoiding random walks (SARWs) under physiological conditions. Here, we tested how temperature and ionic conditions influence the dimensions of the N-terminal domain of pertactin (PNt), an IDP with an amino acid composition typical of folded proteins. While PNt contracts somewhat with temperature, it nevertheless remains expanded over 10-58°C, with a Flory exponent, ν, >0.50. Both low and high ionic strength also produce contraction in PNt, but this contraction is mitigated by reducing charge segregation. With 46% glycine and low hydrophobicity, the reduced form of snow flea anti-freeze protein (red-sfAFP) is unaffected by temperature and ionic strength and persists as a near-SARW, ν ~ 0.54, arguing that the thermal contraction of PNt is due to stronger interactions between hydrophobic side chains. Additionally, red-sfAFP is a proxy for the polypeptide backbone, which has been thought to collapse in water. Increasing the glycine segregation in red-sfAFP had minimal effect on ν. Water remained a good solvent even with 21 consecutive glycine residues (ν > 0.5), and red-sfAFP variants lacked stable backbone hydrogen bonds according to hydrogen exchange. Similarly, changing glycine segregation has little impact on ν in other glycine-rich proteins. These findings underscore the generality that many disordered states can be expanded and unstructured, and that the hydrophobic effect alone is insufficient to drive significant chain collapse for typical protein sequences.
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Affiliation(s)
- Michael C. Baxa
- Department of Biochemistry & Molecular BiologyThe University of ChicagoChicagoIllinoisUSA
| | - Xiaoxuan Lin
- Department of Biochemistry & Molecular BiologyThe University of ChicagoChicagoIllinoisUSA
| | - Cedrick D. Mukinay
- Department of Chemistry & BiochemistryUniversity of Notre DameNotre DameIndianaUSA
| | - Srinivas Chakravarthy
- Biophysics Collaborative Access Team (BioCAT), Center for Synchrotron Radiation Research and Instrumentation and Department of Biological and Chemical SciencesIllinois Institute of TechnologyChicagoIllinoisUSA
- Present address:
Cytiva, Fast TrakMarlboroughMAUSA
| | | | - Sarah Antilla
- Department of Materials Science and EngineeringMassachusetts Institute of TechnologyCambridgeMassachusettsUSA
| | - Nina Hartrampf
- Department of ChemistryMassachusetts Institute of TechnologyCambridgeMassachusettsUSA
- Present address:
Department of ChemistryUniversity of ZurichSwitzerland
| | - Joshua A. Riback
- Graduate Program in Biophysical ScienceUniversity of ChicagoChicagoIllinoisUSA
- Present address:
Department of Molecular and Cellular BiologyBaylor College of MedicineHoustonTXUSA
| | - Isabelle A. Gagnon
- Department of Biochemistry & Molecular BiologyThe University of ChicagoChicagoIllinoisUSA
| | - Bradley L. Pentelute
- Department of ChemistryMassachusetts Institute of TechnologyCambridgeMassachusettsUSA
| | - Patricia L. Clark
- Department of Chemistry & BiochemistryUniversity of Notre DameNotre DameIndianaUSA
| | - Tobin R. Sosnick
- Department of Biochemistry & Molecular BiologyThe University of ChicagoChicagoIllinoisUSA
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3
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Truong HP, Saleh OA. Magnetic tweezers characterization of the entropic elasticity of intrinsically disordered proteins and peptoids. Methods Enzymol 2024; 694:209-236. [PMID: 38492952 DOI: 10.1016/bs.mie.2023.12.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2024]
Abstract
Understanding the conformational behavior of biopolymers is essential to unlocking knowledge of their biophysical mechanisms and functional roles. Single-molecule force spectroscopy can provide a unique perspective on this by exploiting entropic elasticity to uncover key biopolymer structural parameters. A particularly powerful approach involves the use of magnetic tweezers, which can easily generate lower stretching forces (0.1-20 pN). For forces at the low end of this range, the elastic response of biopolymers is sensitive to excluded volume effects, and they can be described by Pincus blob elasticity model that allow robust extraction of the Flory polymer scaling exponent. Here, we detail protocols for the use of magnetic tweezers for force-extension measurements of intrinsically disordered proteins and peptoids. We also discuss procedures for fitting low-force elastic curves to the predictions of polymer physics models to extract key conformational parameters.
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Affiliation(s)
- Hoang P Truong
- Materials Department, University of California, Santa Barbara, CA, United States
| | - Omar A Saleh
- Materials Department, University of California, Santa Barbara, CA, United States; Biomolecular Sciences and Engineering Program, University of California, Santa Barbara, CA, United States; Physics Department, University of California, Santa Barbara, CA, United States.
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4
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Koren G, Meir S, Holschuh L, Mertens HDT, Ehm T, Yahalom N, Golombek A, Schwartz T, Svergun DI, Saleh OA, Dzubiella J, Beck R. Intramolecular structural heterogeneity altered by long-range contacts in an intrinsically disordered protein. Proc Natl Acad Sci U S A 2023; 120:e2220180120. [PMID: 37459524 PMCID: PMC10372579 DOI: 10.1073/pnas.2220180120] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Accepted: 06/02/2023] [Indexed: 07/20/2023] Open
Abstract
Short-range interactions and long-range contacts drive the 3D folding of structured proteins. The proteins' structure has a direct impact on their biological function. However, nearly 40% of the eukaryotes proteome is composed of intrinsically disordered proteins (IDPs) and protein regions that fluctuate between ensembles of numerous conformations. Therefore, to understand their biological function, it is critical to depict how the structural ensemble statistics correlate to the IDPs' amino acid sequence. Here, using small-angle X-ray scattering and time-resolved Förster resonance energy transfer (trFRET), we study the intramolecular structural heterogeneity of the neurofilament low intrinsically disordered tail domain (NFLt). Using theoretical results of polymer physics, we find that the Flory scaling exponent of NFLt subsegments correlates linearly with their net charge, ranging from statistics of ideal to self-avoiding chains. Surprisingly, measuring the same segments in the context of the whole NFLt protein, we find that regardless of the peptide sequence, the segments' structural statistics are more expanded than when measured independently. Our findings show that while polymer physics can, to some level, relate the IDP's sequence to its ensemble conformations, long-range contacts between distant amino acids play a crucial role in determining intramolecular structures. This emphasizes the necessity of advanced polymer theories to fully describe IDPs ensembles with the hope that it will allow us to model their biological function.
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Affiliation(s)
- Gil Koren
- The School of Physics and Astronomy, Department of Condensed Matter, Tel Aviv University, Tel Aviv69978, Israel
- The Center for Physics and Chemistry of Living Systems, Tel Aviv University, Tel Aviv69978, Israel
- The Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel Aviv69978, Israel
| | - Sagi Meir
- The School of Physics and Astronomy, Department of Condensed Matter, Tel Aviv University, Tel Aviv69978, Israel
- The Center for Physics and Chemistry of Living Systems, Tel Aviv University, Tel Aviv69978, Israel
- The Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel Aviv69978, Israel
| | - Lennard Holschuh
- Applied Theoretical Physics-Computational Physics, Physikalisches Institut, Albert-Ludwigs-Universit Freiburg, FreiburgD-79104, Germany
| | | | - Tamara Ehm
- The School of Physics and Astronomy, Department of Condensed Matter, Tel Aviv University, Tel Aviv69978, Israel
- The Center for Physics and Chemistry of Living Systems, Tel Aviv University, Tel Aviv69978, Israel
- The Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel Aviv69978, Israel
- Faculty of Physics and Center for NanoScience, Ludwig-Maximilians-Universität, MünchenD-80539, Germany
| | - Nadav Yahalom
- The Center for Physics and Chemistry of Living Systems, Tel Aviv University, Tel Aviv69978, Israel
- The Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel Aviv69978, Israel
- School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences and Tel Aviv University Center for Light–Matter Interaction, Tel Aviv University, Tel Aviv6997801, Israel
| | - Adina Golombek
- The Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel Aviv69978, Israel
- School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences and Tel Aviv University Center for Light–Matter Interaction, Tel Aviv University, Tel Aviv6997801, Israel
| | - Tal Schwartz
- The Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel Aviv69978, Israel
- School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences and Tel Aviv University Center for Light–Matter Interaction, Tel Aviv University, Tel Aviv6997801, Israel
| | - Dmitri I. Svergun
- European Molecular Biology Laboratory, Hamburg Unit, Hamburg22607, Germany
| | - Omar A. Saleh
- BMSE Program, University of California, Santa Barbara, CA93110
- Materials Department, University of California, Santa Barbara, CA93110
| | - Joachim Dzubiella
- Applied Theoretical Physics-Computational Physics, Physikalisches Institut, Albert-Ludwigs-Universit Freiburg, FreiburgD-79104, Germany
- Cluster of Excellence livMatS @ FIT–Freiburg Center for Interactive Materials and Bioinspired Technologies, Albert-Ludwigs-Universit Freiburg, FreiburgD-79104, Germany
| | - Roy Beck
- The School of Physics and Astronomy, Department of Condensed Matter, Tel Aviv University, Tel Aviv69978, Israel
- The Center for Physics and Chemistry of Living Systems, Tel Aviv University, Tel Aviv69978, Israel
- The Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel Aviv69978, Israel
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5
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McDonnell RT, Elcock AH. AutoRNC: an automated modeling program for building atomic models of ribosome-nascent chain complexes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.14.544999. [PMID: 37398297 PMCID: PMC10312685 DOI: 10.1101/2023.06.14.544999] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/04/2023]
Abstract
The interpretation of experimental studies of co-translational protein folding often benefits from the use of computational methods that seek to model the nascent chain and its interactions with the ribosome. Ribosome-nascent chain (RNC) constructs studied experimentally can vary significantly in size and the extent to which they contain secondary and tertiary structure, and building realistic 3D models of them therefore often requires expert knowledge. To circumvent this issue, we describe here AutoRNC, an automated modeling program capable of constructing large numbers of plausible atomic models of RNCs within minutes. AutoRNC takes input from the user specifying any regions of the nascent chain that contain secondary or tertiary structure and attempts to build conformations compatible with those specifications - and with the constraints imposed by the ribosome - by sampling and progressively piecing together dipeptide conformations extracted from the RCSB. We first show that conformations of completely unfolded proteins built by AutoRNC in the absence of the ribosome have radii of gyration that match well with the corresponding experimental data. We then show that AutoRNC can build plausible conformations for a wide range of RNC constructs for which experimental data have already been reported. Since AutoRNC requires only modest computational resources, we anticipate that it will prove to be a useful hypothesis generator for experimental studies, for example, in providing indications of whether designed constructs are likely to be capable of folding, as well as providing useful starting points for downstream atomic or coarse-grained simulations of the conformational dynamics of RNCs.
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6
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Paladino A, Vitagliano L, Graziano G. The Action of Chemical Denaturants: From Globular to Intrinsically Disordered Proteins. BIOLOGY 2023; 12:biology12050754. [PMID: 37237566 DOI: 10.3390/biology12050754] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Revised: 05/15/2023] [Accepted: 05/18/2023] [Indexed: 05/28/2023]
Abstract
Proteins perform their many functions by adopting either a minimal number of strictly similar conformations, the native state, or a vast ensemble of highly flexible conformations. In both cases, their structural features are highly influenced by the chemical environment. Even though a plethora of experimental studies have demonstrated the impact of chemical denaturants on protein structure, the molecular mechanism underlying their action is still debated. In the present review, after a brief recapitulation of the main experimental data on protein denaturants, we survey both classical and more recent interpretations of the molecular basis of their action. In particular, we highlight the differences and similarities of the impact that denaturants have on different structural classes of proteins, i.e., globular, intrinsically disordered (IDP), and amyloid-like assemblies. Particular attention has been given to the IDPs, as recent studies are unraveling their fundamental importance in many physiological processes. The role that computation techniques are expected to play in the near future is illustrated.
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Affiliation(s)
- Antonella Paladino
- Institute of Biostructures and Bioimaging, CNR, Via Pietro Castellino 111, 80131 Naples, Italy
| | - Luigi Vitagliano
- Institute of Biostructures and Bioimaging, CNR, Via Pietro Castellino 111, 80131 Naples, Italy
| | - Giuseppe Graziano
- Department of Science and Technology, University of Sannio, via Francesco de Sanctis snc, 82100 Benevento, Italy
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7
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Vovk A, Zilman A. Effects of Sequence Composition, Patterning and Hydrodynamics on the Conformation and Dynamics of Intrinsically Disordered Proteins. Int J Mol Sci 2023; 24:1444. [PMID: 36674958 PMCID: PMC9867189 DOI: 10.3390/ijms24021444] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Revised: 12/24/2022] [Accepted: 12/25/2022] [Indexed: 01/13/2023] Open
Abstract
Intrinsically disordered proteins (IDPs) and intrinsically disordered regions (IDRs) perform diverse functions in cellular organization, transport and signaling. Unlike the well-defined structures of the classical natively folded proteins, IDPs and IDRs dynamically span large conformational and structural ensembles. This dynamic disorder impedes the study of the relationship between the amino acid sequences of the IDPs and their spatial structures and dynamics, with different experimental techniques often offering seemingly contradictory results. Although experimental and theoretical evidence indicates that some IDP properties can be understood based on their average biophysical properties and amino acid composition, other aspects of IDP function are dictated by the specifics of the amino acid sequence. We investigate the effects of several key variables on the dimensions and the dynamics of IDPs using coarse-grained polymer models. We focus on the sequence "patchiness" informed by the sequence and biophysical properties of different classes of IDPs-and in particular FG nucleoporins of the nuclear pore complex (NPC). We show that the sequence composition and patterning are well reflected in the global conformational variables such as the radius of gyration and hydrodynamic radius, while the end-to-end distance and dynamics are highly sequence-specific. We find that in good solvent conditions highly heterogeneous sequences of IDPs can be well mapped onto averaged minimal polymer models for the purpose of prediction of the IDPs dimensions and dynamic relaxation times. The coarse-grained simulations are in a good agreement with the results of atomistic MD. We discuss the implications of these results for the interpretation of the recent experimental measurements, and for the further applications of mesoscopic models of FG nucleoporins and IDPs more broadly.
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Affiliation(s)
- Andrei Vovk
- Department of Physics, University of Toronto, 60 St George Street, Toronto, ON M1M 2P7, Canada
| | - Anton Zilman
- Department of Physics, University of Toronto, 60 St George Street, Toronto, ON M1M 2P7, Canada
- Institute for Biomedical Engineering, University of Toronto, 164 College Street, Toronto, ON M5S 3G9, Canada
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8
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Pastore A, Temussi PA. The Protein Unfolded State: One, No One and One Hundred Thousand. J Am Chem Soc 2022; 144:22352-22357. [PMID: 36450361 PMCID: PMC9756289 DOI: 10.1021/jacs.2c07696] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Indexed: 12/03/2022]
Abstract
Many in vitro studies, in which proteins have been unfolded by the action of a variety of physical or chemical agents, have led to the definition of a folded versus an unfolded state and to the question of what is the nature of the unfolded state. The unstructured nature of this state could suggest that "the" unfolded state is a unique entity which holds true for all kinds of unfolding processes. This assumption has to be questioned because the unfolding processes under different stress conditions are dictated by entirely different mechanisms. As a consequence, it can be easily understood that the final state, generically referred to as "the unfolded state", can be completely different for each of the unfolding processes. The present review examines recent data on the characteristics of the unfolded states emerging from experiments under different conditions, focusing specific attention to the level of compaction of the unfolded species.
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Affiliation(s)
| | - Piero Andrea Temussi
- UK Dementia Research Institute at
the Maurice Wohl Institute of King’s College London, London, SE5 9RT, United Kingdom
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9
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Barth A, Opanasyuk O, Peulen TO, Felekyan S, Kalinin S, Sanabria H, Seidel CAM. Unraveling multi-state molecular dynamics in single-molecule FRET experiments. I. Theory of FRET-lines. J Chem Phys 2022; 156:141501. [PMID: 35428384 PMCID: PMC9014241 DOI: 10.1063/5.0089134] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 02/27/2022] [Indexed: 01/31/2023] Open
Abstract
Conformational dynamics of biomolecules are of fundamental importance for their function. Single-molecule studies of Förster Resonance Energy Transfer (smFRET) between a tethered donor and acceptor dye pair are a powerful tool to investigate the structure and dynamics of labeled molecules. However, capturing and quantifying conformational dynamics in intensity-based smFRET experiments remains challenging when the dynamics occur on the sub-millisecond timescale. The method of multiparameter fluorescence detection addresses this challenge by simultaneously registering fluorescence intensities and lifetimes of the donor and acceptor. Together, two FRET observables, the donor fluorescence lifetime τD and the intensity-based FRET efficiency E, inform on the width of the FRET efficiency distribution as a characteristic fingerprint for conformational dynamics. We present a general framework for analyzing dynamics that relates average fluorescence lifetimes and intensities in two-dimensional burst frequency histograms. We present parametric relations of these observables for interpreting the location of FRET populations in E-τD diagrams, called FRET-lines. To facilitate the analysis of complex exchange equilibria, FRET-lines serve as reference curves for a graphical interpretation of experimental data to (i) identify conformational states, (ii) resolve their dynamic connectivity, (iii) compare different kinetic models, and (iv) infer polymer properties of unfolded or intrinsically disordered proteins. For a simplified graphical analysis of complex kinetic networks, we derive a moment-based representation of the experimental data that decouples the motion of the fluorescence labels from the conformational dynamics of the biomolecule. Importantly, FRET-lines facilitate exploring complex dynamic models via easily computed experimental observables. We provide extensive computational tools to facilitate applying FRET-lines.
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Affiliation(s)
- Anders Barth
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, Düsseldorf, Germany
| | - Oleg Opanasyuk
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, Düsseldorf, Germany
| | - Thomas-Otavio Peulen
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, Düsseldorf, Germany
| | - Suren Felekyan
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, Düsseldorf, Germany
| | - Stanislav Kalinin
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, Düsseldorf, Germany
| | - Hugo Sanabria
- Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29631, USA
| | - Claus A. M. Seidel
- Institut für Physikalische Chemie, Lehrstuhl für Molekulare Physikalische Chemie, Heinrich-Heine-Universität, Düsseldorf, Germany
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10
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Abstract
Proteins have dynamic structures that undergo chain motions on time scales spanning from picoseconds to seconds. Resolving the resultant conformational heterogeneity is essential for gaining accurate insight into fundamental mechanistic aspects of the protein folding reaction. The use of high-resolution structural probes, sensitive to population distributions, has begun to enable the resolution of site-specific conformational heterogeneity at different stages of the folding reaction. Different states populated during protein folding, including the unfolded state, collapsed intermediate states, and even the native state, are found to possess significant conformational heterogeneity. Heterogeneity in protein folding and unfolding reactions originates from the reduced cooperativity of various kinds of physicochemical interactions between various structural elements of a protein, and between a protein and solvent. Heterogeneity may arise because of functional or evolutionary constraints. Conformational substates within the unfolded state and the collapsed intermediates that exchange at rates slower than the subsequent folding steps give rise to heterogeneity on the protein folding pathways. Multiple folding pathways are likely to represent distinct sequences of structure formation. Insight into the nature of the energy barriers separating different conformational states populated during (un)folding can also be obtained by resolving heterogeneity.
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Affiliation(s)
- Sandhya Bhatia
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India.,Indian Institute of Science Education and Research, Pune 411008, India
| | - Jayant B Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India.,Indian Institute of Science Education and Research, Pune 411008, India
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11
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Naudi-Fabra S, Tengo M, Jensen MR, Blackledge M, Milles S. Quantitative Description of Intrinsically Disordered Proteins Using Single-Molecule FRET, NMR, and SAXS. J Am Chem Soc 2021; 143:20109-20121. [PMID: 34817999 PMCID: PMC8662727 DOI: 10.1021/jacs.1c06264] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Indexed: 12/18/2022]
Abstract
Studying the conformational landscape of intrinsically disordered and partially folded proteins is challenging and only accessible to a few solution state techniques, such as nuclear magnetic resonance (NMR), small-angle scattering techniques, and single-molecule Förster resonance energy transfer (smFRET). While each of the techniques is sensitive to different properties of the disordered chain, such as local structural propensities, overall dimension, or intermediate- and long-range contacts, conformational ensembles describing intrinsically disordered proteins (IDPs) accurately should ideally respect all of these properties. Here we develop an integrated approach using a large set of FRET efficiencies and fluorescence lifetimes, NMR chemical shifts, and paramagnetic relaxation enhancements (PREs), as well as small-angle X-ray scattering (SAXS) to derive quantitative conformational ensembles in agreement with all parameters. Our approach is tested using simulated data (five sets of PREs and 15 FRET efficiencies) and validated experimentally on the example of the disordered domain of measles virus phosphoprotein, providing new insights into the conformational landscape of this viral protein that comprises transient structural elements and is more compact than an unfolded chain throughout its length. Rigorous cross-validation using FRET efficiencies, fluorescence lifetimes, and SAXS demonstrates the predictive nature of the calculated conformational ensembles and underlines the potential of this strategy in integrative dynamic structural biology.
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Affiliation(s)
- Samuel Naudi-Fabra
- Institut de Biologie Structurale,
Université Grenoble Alpes-CEA-CNRS, 71, Avenue des Martyrs, 38044 Grenoble, France
| | - Maud Tengo
- Institut de Biologie Structurale,
Université Grenoble Alpes-CEA-CNRS, 71, Avenue des Martyrs, 38044 Grenoble, France
| | - Malene Ringkjøbing Jensen
- Institut de Biologie Structurale,
Université Grenoble Alpes-CEA-CNRS, 71, Avenue des Martyrs, 38044 Grenoble, France
| | - Martin Blackledge
- Institut de Biologie Structurale,
Université Grenoble Alpes-CEA-CNRS, 71, Avenue des Martyrs, 38044 Grenoble, France
| | - Sigrid Milles
- Institut de Biologie Structurale,
Université Grenoble Alpes-CEA-CNRS, 71, Avenue des Martyrs, 38044 Grenoble, France
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12
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Ortega G, Aguilar MA, Gautam BK, Plaxco KW. The effect of charged residue substitutions on the thermodynamics of protein-surface interactions. Protein Sci 2021; 30:2408-2417. [PMID: 34719069 DOI: 10.1002/pro.4215] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Revised: 10/20/2021] [Accepted: 10/22/2021] [Indexed: 01/07/2023]
Abstract
The interactions of proteins with surfaces are important in both biological processes and biotechnologies. In contrast to decades of study regarding the biophysics of proteins in bulk solution, however, our mechanistic understanding of the biophysics of proteins interacting with surfaces remains largely qualitative. In response, we have set to explore quantitatively the thermodynamics of protein-surface interactions. In this work, we explore systematically the role of electrostatics in modulating the interaction between proteins and charged surfaces. In particular, we use electrochemistry to explore the extent to which a macroscopic, hydroxyl-coated surface held at a slightly negative potential affects the folding thermodynamics of surface-attached protein variants with different composition of charged amino acids. Doing so, we find that attachment to the surface generally leads to a net stabilization, presumably due to excluded volume effects that reduce the entropy of the unfolded state. The magnitude of this stabilization, however, is strongly correlated with the charged-residue content of the protein. In particular, we find statistically significant correlations with both the net charge of the protein, with greater negative charge leading to less stabilization by the surface, and with the number of arginines, with more arginines leading to greater stabilization. Such findings refine our understanding of protein-surface interactions, providing in turn a guiding rationale to achieve the functional deposition of proteins on artificial surfaces for implementation in, for example, protein-based biotechnologies.
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Affiliation(s)
- Gabriel Ortega
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California, USA.,Center for Bioengineering, University of California Santa Barbara, Santa Barbara, California, USA.,Precision Medicine and Metabolism Laboratory, CIC bioGUNE, Basque Research and Technology Alliance, Parque Tecnológico de Bizkaia, Derio, Spain.,Ikerbasque, Basque Foundation for Science, Bilbao, Bizkaia, Spain
| | - Miguel A Aguilar
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California, USA
| | - Bishal K Gautam
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California, USA
| | - Kevin W Plaxco
- Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California, USA.,Center for Bioengineering, University of California Santa Barbara, Santa Barbara, California, USA
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13
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Alston JJ, Soranno A, Holehouse AS. Integrating single-molecule spectroscopy and simulations for the study of intrinsically disordered proteins. Methods 2021; 193:116-135. [PMID: 33831596 PMCID: PMC8713295 DOI: 10.1016/j.ymeth.2021.03.018] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Revised: 03/25/2021] [Accepted: 03/31/2021] [Indexed: 12/21/2022] Open
Abstract
Over the last two decades, intrinsically disordered proteins and protein regions (IDRs) have emerged from a niche corner of biophysics to be recognized as essential drivers of cellular function. Various techniques have provided fundamental insight into the function and dysfunction of IDRs. Among these techniques, single-molecule fluorescence spectroscopy and molecular simulations have played a major role in shaping our modern understanding of the sequence-encoded conformational behavior of disordered proteins. While both techniques are frequently used in isolation, when combined they offer synergistic and complementary information that can help uncover complex molecular details. Here we offer an overview of single-molecule fluorescence spectroscopy and molecular simulations in the context of studying disordered proteins. We discuss the various means in which simulations and single-molecule spectroscopy can be integrated, and consider a number of studies in which this integration has uncovered biological and biophysical mechanisms.
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Affiliation(s)
- Jhullian J Alston
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis 63110, MO, USA; Center for Science and Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis 63130, MO, USA
| | - Andrea Soranno
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis 63110, MO, USA; Center for Science and Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis 63130, MO, USA.
| | - Alex S Holehouse
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis 63110, MO, USA; Center for Science and Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis 63130, MO, USA.
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14
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Song J, Li J, Chan HS. Small-Angle X-ray Scattering Signatures of Conformational Heterogeneity and Homogeneity of Disordered Protein Ensembles. J Phys Chem B 2021; 125:6451-6478. [PMID: 34115515 DOI: 10.1021/acs.jpcb.1c02453] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
An accurate account of disordered protein conformations is of central importance to deciphering the physicochemical basis of biological functions of intrinsically disordered proteins and the folding-unfolding energetics of globular proteins. Physically, disordered ensembles of nonhomopolymeric polypeptides are expected to be heterogeneous, i.e., they should differ from those homogeneous ensembles of homopolymers that harbor an essentially unique relationship between average values of end-to-end distance REE and radius of gyration Rg. It was posited recently, however, that small-angle X-ray scattering (SAXS) data on conformational dimensions of disordered proteins can be rationalized almost exclusively by homopolymer ensembles. Assessing this perspective, chain-model simulations are used to evaluate the discriminatory power of SAXS-determined molecular form factors (MFFs) with regard to homogeneous versus heterogeneous ensembles. The general approach adopted here is not bound by any assumption about ensemble encodability, in that the postulated heterogeneous ensembles we evaluated are not restricted to those entailed by simple interaction schemes. Our analysis of MFFs for certain heterogeneous ensembles with more narrowly distributed REE and Rg indicates that while they deviate from MFFs of homogeneous ensembles, the differences can be rather small. Remarkably, some heterogeneous ensembles with asphericity and REE drastically different from those of homogeneous ensembles can nonetheless exhibit practically identical MFFs, demonstrating that SAXS MFFs do not afford unique characterizations of basic properties of conformational ensembles in general. In other words, the ensemble to MFF mapping is practically many-to-one and likely nonsmooth. Heteropolymeric variations of the REE-Rg relationship were further showcased using an analytical perturbation theory developed here for flexible heteropolymers. Ramifications of our findings for interpretation of experimental data are discussed.
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Affiliation(s)
- Jianhui Song
- School of Polymer Science and Engineering, Qingdao University of Science and Technology, 53 Zhengzhou Road, Qingdao 266042, China
| | - Jichen Li
- School of Polymer Science and Engineering, Qingdao University of Science and Technology, 53 Zhengzhou Road, Qingdao 266042, China
| | - Hue Sun Chan
- Department of Biochemistry, University of Toronto Faculty of Medicine, Toronto, Ontario M5S 1A8, Canada
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15
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Bhatia S, Krishnamoorthy G, Udgaonkar JB. Resolving Site-Specific Heterogeneity of the Unfolded State under Folding Conditions. J Phys Chem Lett 2021; 12:3295-3302. [PMID: 33764778 DOI: 10.1021/acs.jpclett.1c00098] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Understanding the properties of the unfolded state under folding conditions is of fundamental importance for gaining mechanistic insight into folding as well as misfolding reactions. Toward achieving this objective, the folding reaction of a small protein, monellin, has been resolved structurally and temporally, with the use of the multisite time-resolved FRET methodology. The present study establishes that the initial polypeptide chain collapse is not only heterogeneous but also structurally asymmetric and nonuniform. The population-averaged size for the segments spanning parts of the β-sheet decreases much more than that for the α-helix. Multisite measurements enabled specific and nonspecific components of the initial chain collapse to be discerned. The expanded and compact intermediate subensembles have the properties of a nonspecifically collapsed (hence, random-coil-like) and specifically collapsed (hence, globular) polymer, respectively. During subsequent folding, both the subensembles underwent contraction to varying extents at the four monitored segments, which was close to gradual in nature. The expanded intermediate subensemble exhibited an additional very slow contraction, suggestive of the presence of non-native interactions that result in a higher effective viscosity slowing down intrachain motions under folding conditions.
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Affiliation(s)
- Sandhya Bhatia
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560 065, India
- Indian Institute of Science Education and Research, Pune 411 008, India
| | | | - Jayant B Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560 065, India
- Indian Institute of Science Education and Research, Pune 411 008, India
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16
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Kuwajima K. The Molten Globule, and Two-State vs. Non-Two-State Folding of Globular Proteins. Biomolecules 2020; 10:biom10030407. [PMID: 32155758 PMCID: PMC7175247 DOI: 10.3390/biom10030407] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 03/03/2020] [Accepted: 03/06/2020] [Indexed: 11/16/2022] Open
Abstract
From experimental studies of protein folding, it is now clear that there are two types of folding behavior, i.e., two-state folding and non-two-state folding, and understanding the relationships between these apparently different folding behaviors is essential for fully elucidating the molecular mechanisms of protein folding. This article describes how the presence of the two types of folding behavior has been confirmed experimentally, and discusses the relationships between the two-state and the non-two-state folding reactions, on the basis of available data on the correlations of the folding rate constant with various structure-based properties, which are determined primarily by the backbone topology of proteins. Finally, a two-stage hierarchical model is proposed as a general mechanism of protein folding. In this model, protein folding occurs in a hierarchical manner, reflecting the hierarchy of the native three-dimensional structure, as embodied in the case of non-two-state folding with an accumulation of the molten globule state as a folding intermediate. The two-state folding is thus merely a simplified version of the hierarchical folding caused either by an alteration in the rate-limiting step of folding or by destabilization of the intermediate.
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Affiliation(s)
- Kunihiro Kuwajima
- Department of Physics, School of Science, the University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; ; Tel.: +81-90-5435-6540
- School of Computational Sciences, Korea Institute for Advanced Study (KIAS), Seoul 02455, Korea
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17
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Ramanujam V, Alderson TR, Pritišanac I, Ying J, Bax A. Protein structural changes characterized by high-pressure, pulsed field gradient diffusion NMR spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 312:106701. [PMID: 32113145 PMCID: PMC7153785 DOI: 10.1016/j.jmr.2020.106701] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 02/16/2020] [Accepted: 02/17/2020] [Indexed: 06/10/2023]
Abstract
Pulsed-field gradient NMR spectroscopy is widely used to measure the translational diffusion and hydrodynamic radius (Rh) of biomolecules in solution. For unfolded proteins, the Rh provides a sensitive reporter on the ensemble-averaged conformation and the extent of polypeptide chain expansion as a function of added denaturant. Hydrostatic pressure is a convenient and reversible alternative to chemical denaturants for the study of protein folding, and enables NMR measurements to be performed on a single sample. While the impact of pressure on the viscosity of water is well known, and our water diffusivity measurements agree closely with theoretical expectations, we find that elevated pressures increase the Rh of dioxane and other small molecules by amounts that correlate with their hydrophobicity, with parallel increases in rotational friction indicated by 13C longitudinal relaxation times. These data point to a tighter coupling with water for hydrophobic surfaces at elevated pressures. Translational diffusion measurement of the unfolded state of a pressure-sensitized ubiquitin mutant (VA2-ubiquitin) as a function of hydrostatic pressure or urea concentration shows that Rh values of both the folded and the unfolded states remain nearly invariant. At ca 23 Å, the Rh of the fully pressure-denatured state is essentially indistinguishable from the urea-denatured state, and close to the value expected for an idealized random coil of 76 residues. The intrinsically disordered protein (IDP) α-synuclein shows slight compaction at pressures above 2 kbar. Diffusion of unfolded ubiquitin and α-synuclein is significantly impacted by sample concentration, indicating that quantitative measurements need to be carried out under dilute conditions.
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Affiliation(s)
- Venkatraman Ramanujam
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA; Institute of Biophysical Chemistry, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt am Main, 60438 Frankfurt am Main, Germany
| | - T Reid Alderson
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA; Institute of Biophysical Chemistry, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt am Main, 60438 Frankfurt am Main, Germany
| | - Iva Pritišanac
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA; Institute of Biophysical Chemistry, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt am Main, 60438 Frankfurt am Main, Germany
| | - Jinfa Ying
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA; Institute of Biophysical Chemistry, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt am Main, 60438 Frankfurt am Main, Germany
| | - Ad Bax
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA; Institute of Biophysical Chemistry, Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt am Main, 60438 Frankfurt am Main, Germany.
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18
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Clark PL, Plaxco KW, Sosnick TR. Water as a Good Solvent for Unfolded Proteins: Folding and Collapse are Fundamentally Different. J Mol Biol 2020; 432:2882-2889. [PMID: 32044346 DOI: 10.1016/j.jmb.2020.01.031] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Revised: 01/28/2020] [Accepted: 01/29/2020] [Indexed: 12/30/2022]
Abstract
The argument that the hydrophobic effect is the primary effect driving the folding of globular proteins is nearly universally accepted (including by the authors). But does this view also imply that water is a "poor" solvent for the unfolded states of these same proteins? Here we argue that the answer is "no," that is, folding to a well-packed, extensively hydrogen-bonded native structure differs fundamentally from the nonspecific chain collapse that defines a poor solvent. Thus, the observation that a protein folds in water does not necessitate that water is a poor solvent for its unfolded state. Indeed, chain-solvent interactions that are marginally more favorable than nonspecific intrachain interactions are beneficial to protein function because they destabilize deleterious misfolded conformations and inter-chain interactions.
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Affiliation(s)
- Patricia L Clark
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN, 46556, USA.
| | - Kevin W Plaxco
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA, 93106, USA.
| | - Tobin R Sosnick
- Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, 60637, USA.
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19
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Best RB. Emerging consensus on the collapse of unfolded and intrinsically disordered proteins in water. Curr Opin Struct Biol 2020; 60:27-38. [PMID: 31805437 PMCID: PMC7472963 DOI: 10.1016/j.sbi.2019.10.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Revised: 10/23/2019] [Accepted: 10/24/2019] [Indexed: 11/16/2022]
Abstract
Establishing the degree of collapse of unfolded or disordered proteins is a fundamental problem in biophysics, because of its relation to protein folding and to the function of intrinsically disordered proteins. However, until recently, different experiments gave qualitatively different results on collapse and there were large discrepancies between experiments and all-atom simulations. New methodology introduced in the past three years has helped to resolve the differences between experiments, and improvements in simulations have closed the gap between experiment and simulation. These advances have led to an emerging consensus on the collapse of disordered proteins in water.
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Affiliation(s)
- Robert B Best
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, United States
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20
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Observation of Continuous Contraction and a Metastable Misfolded State during the Collapse and Folding of a Small Protein. J Mol Biol 2019; 431:3814-3826. [DOI: 10.1016/j.jmb.2019.07.024] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Revised: 07/12/2019] [Accepted: 07/12/2019] [Indexed: 01/22/2023]
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21
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Thirumalai D, Samanta HS, Maity H, Reddy G. Universal Nature of Collapsibility in the Context of Protein Folding and Evolution. Trends Biochem Sci 2019; 44:675-687. [DOI: 10.1016/j.tibs.2019.04.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 04/03/2019] [Accepted: 04/04/2019] [Indexed: 12/21/2022]
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22
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Unfolded states under folding conditions accommodate sequence-specific conformational preferences with random coil-like dimensions. Proc Natl Acad Sci U S A 2019; 116:12301-12310. [PMID: 31167941 PMCID: PMC7056937 DOI: 10.1073/pnas.1818206116] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Proteins are marginally stable molecules that fluctuate between folded and unfolded states. Here, we provide a high-resolution description of unfolded states under refolding conditions for the N-terminal domain of the L9 protein (NTL9). We use a combination of time-resolved Förster resonance energy transfer (FRET) based on multiple pairs of minimally perturbing labels, time-resolved small-angle X-ray scattering (SAXS), all-atom simulations, and polymer theory. Upon dilution from high denaturant, the unfolded state undergoes rapid contraction. Although this contraction occurs before the folding transition, the unfolded state remains considerably more expanded than the folded state and accommodates a range of local and nonlocal contacts, including secondary structures and native and nonnative interactions. Paradoxically, despite discernible sequence-specific conformational preferences, the ensemble-averaged properties of unfolded states are consistent with those of canonical random coils, namely polymers in indifferent (theta) solvents. These findings are concordant with theoretical predictions based on coarse-grained models and inferences drawn from single-molecule experiments regarding the sequence-specific scaling behavior of unfolded proteins under folding conditions.
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23
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Li M, Cao H, Lai L, Liu Z. Disordered linkers in multidomain allosteric proteins: Entropic effect to favor the open state or enhanced local concentration to favor the closed state? Protein Sci 2019; 27:1600-1610. [PMID: 30019371 DOI: 10.1002/pro.3475] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2018] [Revised: 06/12/2018] [Accepted: 06/24/2018] [Indexed: 12/11/2022]
Abstract
There are many multidomain allosteric proteins where an allosteric signal at the allosteric domain modifies the activity of the functional domain. Intrinsically disordered regions (linkers) are widely involved in this kind of regulation process, but the essential role they play therein is not well understood. Here, we investigated the effect of linkers in stabilizing the open or the closed states of multidomain proteins using combined thermodynamic deduction and coarse-grained molecular dynamics simulations. We revealed that the influence of linker can be fully characterized by an effective local concentration [B]0 . When Kd is smaller than [B]0 , the closed state would be favored; while the open state would be preferred when Kd is larger than [B]0 . We used four protein systems with markedly different domain-domain binding affinity and structural order/disorder as model systems to understand the relationship between [B]0 and the linker length as well as its flexibility. The linker length is the main practical determinant of [B]0 . [B]0 of a flexible linker with 40-60 residues was determined to be in a narrow range of 0.2-0.6 mM, while a too short or too long length would dramatically decrease [B]0 . With the revealed [B]0 range, the introduction of a flexible linker makes the regulation of weakly interacting partners possible.
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Affiliation(s)
- Maodong Li
- Center for Quantitative Biology, Peking University, Beijing, 100871, China
| | - Huaiqing Cao
- College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China
| | - Luhua Lai
- Center for Quantitative Biology, Peking University, Beijing, 100871, China.,College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China.,State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Beijing National Laboratory for Molecular Sciences (BNLMS), Peking University, Beijing, 100871, China
| | - Zhirong Liu
- Center for Quantitative Biology, Peking University, Beijing, 100871, China.,College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, China.,State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Beijing National Laboratory for Molecular Sciences (BNLMS), Peking University, Beijing, 100871, China
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24
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Commonly used FRET fluorophores promote collapse of an otherwise disordered protein. Proc Natl Acad Sci U S A 2019; 116:8889-8894. [PMID: 30992378 DOI: 10.1073/pnas.1813038116] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The dimensions that unfolded proteins, including intrinsically disordered proteins (IDPs), adopt in the absence of denaturant remain controversial. We developed an analysis procedure for small-angle X-ray scattering (SAXS) profiles and used it to demonstrate that even relatively hydrophobic IDPs remain nearly as expanded in water as they are in high denaturant concentrations. In contrast, as demonstrated here, most fluorescence resonance energy transfer (FRET) measurements have indicated that relatively hydrophobic IDPs contract significantly in the absence of denaturant. We use two independent approaches to further explore this controversy. First, using SAXS we show that fluorophores employed in FRET can contribute to the observed discrepancy. Specifically, we find that addition of Alexa-488 to a normally expanded IDP causes contraction by an additional 15%, a value in reasonable accord with the contraction reported in FRET-based studies. Second, using our simulations and analysis procedure to accurately extract both the radius of gyration (Rg) and end-to-end distance (Ree) from SAXS profiles, we tested the recent suggestion that FRET and SAXS results can be reconciled if the Rg and Ree are "uncoupled" (i.e., no longer simply proportional), in contrast to the case for random walk homopolymers. We find, however, that even for unfolded proteins, these two measures of unfolded state dimensions remain proportional. Together, these results suggest that improved analysis procedures and a correction for significant, fluorophore-driven interactions are sufficient to reconcile prior SAXS and FRET studies, thus providing a unified picture of the nature of unfolded polypeptide chains in the absence of denaturant.
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25
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Qu S, Liu C, Liu Q, Wu W, Du B, Wang J. Solvent effect on FRET spectroscopic ruler. J Chem Phys 2018; 148:123331. [PMID: 29604875 DOI: 10.1063/1.5004205] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
A discrepancy has emerged in recent years between single-molecule Förster resonance energy transfer (smFRET) measurements and small angle X-ray scattering (SAXS) or small angle neutron scattering experiments in the study of unfolded or intrinsically disordered proteins in denaturing solutions. Despite significant advances that have been made in identifying various factors which may have contributed to the manifestation of the so-called smFRET-SAXS discrepancy, no consensus has been reached so far on its original source or eventual resolution. In this study, we investigate this problem from the perspective of the solvent effect on FRET spectroscopic ruler (SEFSR), a generic term we use to describe various solvent-dependent factors affecting the accuracy of the FRET experimental method that is known as a "spectroscopic ruler." Some factors belonging to SEFSR, such as direct dye-solvent interaction and labeling configuration, seem to have not received due attention regarding their significance in contributing to the discrepancy. We identify SEFSR by measuring a rigid segment of a double-stranded DNA in various solutions using the smFRET method and evaluate its relative importance in smFRET experiments by measuring segments of a single-stranded DNA and polyethylene glycol (PEG) in solutions. We find that SEFSR can produce non-negligible FRET-inferred interdye distance changes in various solutions, with an intensity following the Hofmeister series in ionic solutions and dependent on labeling configurations. SEFSR is found to be significant in GuHCl and urea solutions, which can fully cover the apparent expansion signal of dye-labeled PEG. Our findings suggest that SEFSR may have played an important role in contributing to the smFRET-SAXS discrepancy.
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Affiliation(s)
- Songyuan Qu
- College of Physics, Jilin University, Changchun, Jilin 130012, People's Republic of China
| | - Chuanbo Liu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People's Republic of China
| | - Qiong Liu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People's Republic of China
| | - Wei Wu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People's Republic of China
| | - Baoji Du
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, People's Republic of China
| | - Jin Wang
- College of Physics, Jilin University, Changchun, Jilin 130012, People's Republic of China
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26
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Holmstrom ED, Holla A, Zheng W, Nettels D, Best RB, Schuler B. Accurate Transfer Efficiencies, Distance Distributions, and Ensembles of Unfolded and Intrinsically Disordered Proteins From Single-Molecule FRET. Methods Enzymol 2018; 611:287-325. [PMID: 30471690 PMCID: PMC8018263 DOI: 10.1016/bs.mie.2018.09.030] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Intrinsically disordered proteins (IDPs) sample structurally diverse ensembles. Characterizing the underlying distributions of conformations is a key step toward understanding the structural and functional properties of IDPs. One increasingly popular method for obtaining quantitative information on intramolecular distances and distributions is single-molecule Förster resonance energy transfer (FRET). Here we describe two essential elements of the quantitative analysis of single-molecule FRET data of IDPs: the sample-specific calibration of the single-molecule instrument that is required for determining accurate transfer efficiencies, and the use of state-of-the-art methods for inferring accurate distance distributions from these transfer efficiencies. First, we illustrate how to quantify the correction factors for instrument calibration with alternating donor and acceptor excitation measurements of labeled samples spanning a wide range of transfer efficiencies. Second, we show how to infer distance distributions based on suitably parameterized simple polymer models, and how to obtain conformational ensembles from Bayesian reweighting of molecular simulations or from parameter optimization in simplified coarse-grained models.
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Affiliation(s)
- Erik D Holmstrom
- Department of Biochemistry, University of Zurich, Zurich, Switzerland.
| | - Andrea Holla
- Department of Biochemistry, University of Zurich, Zurich, Switzerland
| | - Wenwei Zheng
- College of Integrative Sciences and Arts, Arizona State University, Mesa, AZ, United States.
| | - Daniel Nettels
- Department of Biochemistry, University of Zurich, Zurich, Switzerland
| | - Robert B Best
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, United States.
| | - Benjamin Schuler
- Department of Biochemistry, University of Zurich, Zurich, Switzerland; Department of Physics, University of Zurich, Zurich, Switzerland.
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27
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LeBlanc SJ, Kulkarni P, Weninger KR. Single Molecule FRET: A Powerful Tool to Study Intrinsically Disordered Proteins. Biomolecules 2018; 8:biom8040140. [PMID: 30413085 PMCID: PMC6315554 DOI: 10.3390/biom8040140] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Revised: 11/02/2018] [Accepted: 11/06/2018] [Indexed: 12/22/2022] Open
Abstract
Intrinsically disordered proteins (IDPs) are often modeled using ideas from polymer physics that suggest they smoothly explore all corners of configuration space. Experimental verification of this random, dynamic behavior is difficult as random fluctuations of IDPs cannot be synchronized across an ensemble. Single molecule fluorescence (or Förster) resonance energy transfer (smFRET) is one of the few approaches that are sensitive to transient populations of sub-states within molecular ensembles. In some implementations, smFRET has sufficient time resolution to resolve transitions in IDP behaviors. Here we present experimental issues to consider when applying smFRET to study IDP configuration. We illustrate the power of applying smFRET to IDPs by discussing two cases in the literature of protein systems for which smFRET has successfully reported phosphorylation-induced modification (but not elimination) of the disordered properties that have been connected to impacts on the related biological function. The examples we discuss, PAGE4 and a disordered segment of the GluN2B subunit of the NMDA receptor, illustrate the great potential of smFRET to inform how IDP function can be regulated by controlling the detailed ensemble of disordered states within biological networks.
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Affiliation(s)
- Sharonda J LeBlanc
- Department of Physics, North Carolina State University, Raleigh, NC 27695, USA.
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Prakash Kulkarni
- Department of Medical Oncology and Therapeutics Research, City of Hope National Medical Center, Duarte, CA 91010, USA.
| | - Keith R Weninger
- Department of Physics, North Carolina State University, Raleigh, NC 27695, USA.
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28
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Best RB, Zheng W, Borgia A, Buholzer K, Borgia MB, Hofmann H, Soranno A, Nettels D, Gast K, Grishaev A, Schuler B. Comment on "Innovative scattering analysis shows that hydrophobic disordered proteins are expanded in water". Science 2018; 361:361/6405/eaar7101. [PMID: 30166459 DOI: 10.1126/science.aar7101] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Accepted: 07/30/2018] [Indexed: 12/29/2022]
Abstract
Riback et al (Reports, 13 October 2017, p. 238) used small-angle x-ray scattering (SAXS) experiments to infer a degree of compaction for unfolded proteins in water versus chemical denaturant that is highly consistent with the results from Förster resonance energy transfer (FRET) experiments. There is thus no "contradiction" between the two methods, nor evidence to support their claim that commonly used FRET fluorophores cause protein compaction.
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Affiliation(s)
- Robert B Best
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892, USA.
| | - Wenwei Zheng
- College of Integrative Sciences and Arts, Arizona State University, Mesa, AZ 85212, USA
| | - Alessandro Borgia
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
| | - Karin Buholzer
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
| | - Madeleine B Borgia
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
| | - Hagen Hofmann
- Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Andrea Soranno
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Daniel Nettels
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland
| | - Klaus Gast
- Physical Biochemistry, University of Potsdam, 14476 Potsdam, Germany
| | - Alexander Grishaev
- National Institute of Standards and Technology and Institute for Bioscience and Biotechnology Research, Rockville, MD 20850, USA
| | - Benjamin Schuler
- Department of Biochemistry, University of Zurich, 8057 Zurich, Switzerland. .,Department of Physics, University of Zurich, 8057 Zurich, Switzerland
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29
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Riback JA, Bowman MA, Zmyslowski A, Knoverek CR, Jumper J, Kaye EB, Freed KF, Clark PL, Sosnick TR. Response to Comment on “Innovative scattering analysis shows that hydrophobic disordered proteins are expanded in water”. Science 2018; 361:361/6405/eaar7949. [PMID: 30166460 DOI: 10.1126/science.aar7949] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2018] [Accepted: 07/30/2018] [Indexed: 12/30/2022]
Abstract
Best et al. claim that we provide no convincing basis to assert that a discrepancy remains between FRET and SAXS results on the dimensions of disordered proteins under physiological conditions. We maintain that a clear discrepancy is apparent in our and other recent publications, including results shown in the Best et al. comment. A plausible origin is fluorophore interactions in FRET experiments.
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Affiliation(s)
- Joshua A Riback
- Graduate Program in Biophysical Sciences, University of Chicago, Chicago, IL 60637, USA
| | - Micayla A Bowman
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Adam Zmyslowski
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA
| | - Catherine R Knoverek
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
| | - John Jumper
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA
- Department of Chemistry and James Franck Institute, University of Chicago, Chicago, IL 60637, USA
| | - Emily B Kaye
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Karl F Freed
- Department of Chemistry and James Franck Institute, University of Chicago, Chicago, IL 60637, USA
| | - Patricia L Clark
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
| | - Tobin R Sosnick
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA.
- Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA
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30
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Holehouse AS, Pappu RV. Collapse Transitions of Proteins and the Interplay Among Backbone, Sidechain, and Solvent Interactions. Annu Rev Biophys 2018; 47:19-39. [PMID: 29345991 PMCID: PMC10740066 DOI: 10.1146/annurev-biophys-070317-032838] [Citation(s) in RCA: 82] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Proteins can collapse into compact globules or form expanded, solvent-accessible, coil-like conformations. Additionally, they can fold into well-defined three-dimensional structures or remain partially or entirely disordered. Recent discoveries have shown that the tendency for proteins to collapse or remain expanded is not intrinsically coupled to their ability to fold. These observations suggest that proteins do not have to form compact globules in aqueous solutions. They can be intrinsically disordered, collapsed, or expanded, and even form well-folded, elongated structures. This ability to decouple collapse from folding is determined by the sequence details of proteins. In this review, we highlight insights gleaned from studies over the past decade. Using a polymer physics framework, we explain how the interplay among sidechains, backbone units, and solvent determines the driving forces for collapsed versus expanded states in aqueous solvents.
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Affiliation(s)
- Alex S Holehouse
- Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in Saint Louis, Saint Louis, Missouri 63130, USA; ,
| | - Rohit V Pappu
- Department of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in Saint Louis, Saint Louis, Missouri 63130, USA; ,
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31
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Miao Y, Tipakornsaowapak T, Zheng L, Mu Y, Lewellyn E. Phospho-regulation of intrinsically disordered proteins for actin assembly and endocytosis. FEBS J 2018; 285:2762-2784. [PMID: 29722136 DOI: 10.1111/febs.14493] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Revised: 04/04/2018] [Accepted: 04/26/2018] [Indexed: 12/13/2022]
Abstract
Actin filament assembly contributes to the endocytic pathway pleiotropically, with active roles in clathrin-dependent and clathrin-independent endocytosis as well as subsequent endosomal trafficking. Endocytosis comprises a series of dynamic events, including the initiation of membrane curvature, bud invagination, vesicle abscission and subsequent vesicular transport. The ultimate success of endocytosis requires the coordinated activities of proteins that trigger actin polymerization, recruit actin-binding proteins (ABPs) and organize endocytic proteins (EPs) that promote membrane curvature through molecular crowding or scaffolding mechanisms. A particularly interesting phenomenon is that multiple EPs and ABPs contain a substantial percentage of intrinsically disordered regions (IDRs), which can contribute to protein coacervation and phase separation. In addition, intrinsically disordered proteins (IDPs) frequently contain sites for post-translational modifications (PTMs) such as phosphorylation, and these modifications exhibit a high preference for IDR residues [Groban ES et al. (2006) PLoS Comput Biol 2, e32]. PTMs are implicated in regulating protein function by modulating the protein conformation, protein-protein interactions and the transition between order and disorder states of IDPs. The molecular mechanisms by which IDRs of ABPs and EPs fine-tune actin assembly and endocytosis remain mostly unexplored and elusive. In this review, we analyze protein sequences of budding yeast EPs and ABPs, and discuss the potential underlying mechanisms for regulating endocytosis and actin assembly through the emerging concept of IDR-mediated protein multivalency, coacervation, and phase transition, with an emphasis on the phospho-regulation of IDRs. Finally, we summarize the current understanding of how these mechanisms coordinate actin cytoskeleton assembly and membrane curvature formation during endocytosis in budding yeast.
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Affiliation(s)
- Yansong Miao
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.,School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, Singapore
| | | | - Liangzhen Zheng
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Yuguang Mu
- School of Biological Sciences, Nanyang Technological University, Singapore, Singapore
| | - Eric Lewellyn
- Department of Biology, Division of Natural Sciences, St Norbert College, De Pere, WI, USA
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32
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Zheng W, Best RB. An Extended Guinier Analysis for Intrinsically Disordered Proteins. J Mol Biol 2018; 430:2540-2553. [PMID: 29571687 DOI: 10.1016/j.jmb.2018.03.007] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 02/28/2018] [Accepted: 03/12/2018] [Indexed: 12/25/2022]
Abstract
Guinier analysis allows model-free determination of the radius of gyration (Rg) of a biomolecule from X-ray or neutron scattering data, in the limit of very small scattering angles. Its range of validity is well understood for globular proteins, but is known to be more restricted for unfolded or intrinsically disordered proteins (IDPs). We have used ensembles of disordered structures from molecular dynamics simulations to investigate which structural properties cause deviations from the Guinier approximation at small scattering angles. We find that the deviation from the Guinier approximation is correlated with the polymer scaling exponent ν describing the unfolded ensemble. We therefore introduce an empirical, ν-dependent, higher-order correction term, to augment the standard Guinier analysis. We test the new fitting scheme using all-atom simulation data for several IDPs and experimental data for both an IDP and a destabilized mutant of a folded protein. In all cases tested, we achieve an accuracy of the inferred Rg within ∼3% of the true Rg. The method is straightforward to implement and extends the range of validity to a maximum qRg of ∼2 versus ∼1.1 for Guinier analysis. Compared with the Guinier or Debye approaches, our method allows data from wider angles with lower noise to be used to analyze scattering data accurately. In addition to Rg, our fitting scheme also yields estimates of the scaling exponent ν in excellent agreement with the reference ν determined from the underlying molecular ensemble.
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Affiliation(s)
- Wenwei Zheng
- College of Integrative Sciences and Arts, Arizona State University, Mesa, AZ 85212, USA.
| | - Robert B Best
- Laboratory of Chemical Physics, National Institute of Diabetes Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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33
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Takahashi S, Yoshida A, Oikawa H. Hypothesis: structural heterogeneity of the unfolded proteins originating from the coupling of the local clusters and the long-range distance distribution. Biophys Rev 2018; 10:363-373. [PMID: 29446056 DOI: 10.1007/s12551-018-0405-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Accepted: 02/05/2018] [Indexed: 01/22/2023] Open
Abstract
We propose a hypothesis that explains two apparently contradicting observations for the heterogeneity of the unfolded proteins. First, the line confocal method of the single-molecule Förster resonance energy transfer (sm-FRET) spectroscopy revealed that the unfolded proteins possess broad peaks in the FRET efficiency plot, implying the significant heterogeneity that lasts longer than milliseconds. Second, the fluorescence correlation method demonstrated that the unfolded proteins fluctuate in the time scale shorter than 100 ns. To formulate the hypothesis, we first summarize the recent consensus for the structure and dynamics of the unfolded proteins. We next discuss the conventional method of the sm-FRET spectroscopy and its limitations for the analysis of the unfolded proteins, followed by the advantages of the line confocal method that revealed the heterogeneity. Finally, we propose that the structural heterogeneity formed by the local clustering of hydrophobic residues modulates the distribution of the long-range distance between the labeled chromophores, resulting in the broadening of the peak in the FRET efficiency plot. A clustering of hydrophobic residues around the chromophore might further contribute to the broadening. The proposed clusters are important for the understanding of protein folding mechanism.
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Affiliation(s)
- Satoshi Takahashi
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, 980-8577, Japan. .,Department of Chemistry, Graduate school of Science, Tohoku University, Aramaki 6-3, Aoba-ku, Sendai, 980-8578, Japan.
| | - Aya Yoshida
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, 980-8577, Japan.,Department of Chemistry, Graduate school of Science, Tohoku University, Aramaki 6-3, Aoba-ku, Sendai, 980-8578, Japan
| | - Hiroyuki Oikawa
- Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, 980-8577, Japan.,Department of Chemistry, Graduate school of Science, Tohoku University, Aramaki 6-3, Aoba-ku, Sendai, 980-8578, Japan
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34
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Maity H, Reddy G. Thermodynamics and Kinetics of Single-Chain Monellin Folding with Structural Insights into Specific Collapse in the Denatured State Ensemble. J Mol Biol 2018; 430:465-478. [DOI: 10.1016/j.jmb.2017.09.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Revised: 08/28/2017] [Accepted: 09/09/2017] [Indexed: 01/21/2023]
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35
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Song J, Gomes GN, Shi T, Gradinaru CC, Chan HS. Conformational Heterogeneity and FRET Data Interpretation for Dimensions of Unfolded Proteins. Biophys J 2017; 113:1012-1024. [PMID: 28877485 DOI: 10.1016/j.bpj.2017.07.023] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 07/26/2017] [Accepted: 07/31/2017] [Indexed: 12/28/2022] Open
Abstract
A mathematico-physically valid formulation is required to infer properties of disordered protein conformations from single-molecule Förster resonance energy transfer (smFRET). Conformational dimensions inferred by conventional approaches that presume a homogeneous conformational ensemble can be unphysical. When all possible-heterogeneous as well as homogeneous-conformational distributions are taken into account without prejudgment, a single value of average transfer efficiency 〈E〉 between dyes at two chain ends is generally consistent with highly diverse, multiple values of the average radius of gyration 〈Rg〉. Here we utilize unbiased conformational statistics from a coarse-grained explicit-chain model to establish a general logical framework to quantify this fundamental ambiguity in smFRET inference. As an application, we address the long-standing controversy regarding the denaturant dependence of 〈Rg〉 of unfolded proteins, focusing on Protein L as an example. Conventional smFRET inference concluded that 〈Rg〉 of unfolded Protein L is highly sensitive to [GuHCl], but data from SAXS suggested a near-constant 〈Rg〉 irrespective of [GuHCl]. Strikingly, our analysis indicates that although the reported 〈E〉 values for Protein L at [GuHCl] = 1 and 7 M are very different at 0.75 and 0.45, respectively, the Bayesian Rg2 distributions consistent with these two 〈E〉 values overlap by as much as 75%. Our findings suggest, in general, that the smFRET-SAXS discrepancy regarding unfolded protein dimensions likely arise from highly heterogeneous conformational ensembles at low or zero denaturant, and that additional experimental probes are needed to ascertain the nature of this heterogeneity.
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Affiliation(s)
- Jianhui Song
- School of Polymer Science and Engineering, Qingdao University of Science and Technology, Qingdao, Shandong, China; Departments of Biochemistry and Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Gregory-Neal Gomes
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada; Department of Physics, University of Toronto, Toronto, Ontario, Canada
| | - Tongfei Shi
- State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, China
| | - Claudiu C Gradinaru
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, Canada; Department of Physics, University of Toronto, Toronto, Ontario, Canada
| | - Hue Sun Chan
- Departments of Biochemistry and Molecular Genetics, University of Toronto, Toronto, Ontario, Canada.
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36
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Riback JA, Bowman MA, Zmyslowski AM, Knoverek CR, Jumper JM, Hinshaw JR, Kaye EB, Freed KF, Clark PL, Sosnick TR. Innovative scattering analysis shows that hydrophobic disordered proteins are expanded in water. Science 2017; 358:238-241. [PMID: 29026044 PMCID: PMC5959285 DOI: 10.1126/science.aan5774] [Citation(s) in RCA: 154] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 09/07/2017] [Indexed: 01/02/2023]
Abstract
A substantial fraction of the proteome is intrinsically disordered, and even well-folded proteins adopt non-native geometries during synthesis, folding, transport, and turnover. Characterization of intrinsically disordered proteins (IDPs) is challenging, in part because of a lack of accurate physical models and the difficulty of interpreting experimental results. We have developed a general method to extract the dimensions and solvent quality (self-interactions) of IDPs from a single small-angle x-ray scattering measurement. We applied this procedure to a variety of IDPs and found that even IDPs with low net charge and high hydrophobicity remain highly expanded in water, contrary to the general expectation that protein-like sequences collapse in water. Our results suggest that the unfolded state of most foldable sequences is expanded; we conjecture that this property was selected by evolution to minimize misfolding and aggregation.
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Affiliation(s)
- Joshua A Riback
- Graduate Program in Biophysical Sciences, University of Chicago, Chicago, IL 60637, USA
| | - Micayla A Bowman
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Adam M Zmyslowski
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA
| | - Catherine R Knoverek
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
| | - John M Jumper
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA
- Department of Chemistry and James Franck Institute, University of Chicago, Chicago, IL 60637, USA
| | - James R Hinshaw
- Department of Chemistry and James Franck Institute, University of Chicago, Chicago, IL 60637, USA
| | - Emily B Kaye
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Karl F Freed
- Department of Chemistry and James Franck Institute, University of Chicago, Chicago, IL 60637, USA
| | - Patricia L Clark
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA.
| | - Tobin R Sosnick
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA.
- Institute for Biophysical Dynamics, University of Chicago, Chicago, IL 60637, USA
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37
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Abstract
In this review, I discuss the various methods researchers use to unfold proteins in the lab in order to understand protein folding both
in vitro and
in vivo. The four main techniques, chemical-, heat-, pressure- and force-denaturation, produce distinctly different unfolded conformational ensembles. Recent measurements have revealed different folding kinetics from different unfolding mechanisms. Thus, comparing these distinct unfolded ensembles sheds light on the underlying free energy landscape of folding.
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Affiliation(s)
- Lisa J Lapidus
- Department of Physics and Astronomy, Michigan State University, East Lansing, USA
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38
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Ruff KM, Holehouse AS. SAXS versus FRET: A Matter of Heterogeneity? Biophys J 2017; 113:971-973. [PMID: 28821322 DOI: 10.1016/j.bpj.2017.07.024] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Revised: 07/11/2017] [Accepted: 07/12/2017] [Indexed: 11/19/2022] Open
Affiliation(s)
- Kiersten M Ruff
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri.
| | - Alex S Holehouse
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri
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39
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Rahamim G, Amir D, Haas E. Simultaneous Determination of Two Subdomain Folding Rates Using the "Transfer-Quench" Method. Biophys J 2017; 112:1786-1796. [PMID: 28494950 DOI: 10.1016/j.bpj.2017.01.037] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Revised: 12/21/2016] [Accepted: 01/06/2017] [Indexed: 11/29/2022] Open
Abstract
The investigation of the mechanism of protein folding is complicated by the context dependence of the rates of intramolecular contact formation. Methods based on site-specific labeling and ultrafast spectroscopic detection of fluorescence signals were developed for monitoring the rates of individual subdomain folding transitions in situ, in the context of the whole molecule. However, each site-specific labeling modification might affect rates of folding of near-neighbor structural elements, and thus limit the ability to resolve fine differences in rates of folding of these elements. Therefore, it is highly desirable to be able to study the rates of folding of two or more neighboring subdomain structures using a single mutant to facilitate resolution of the order and interdependence of such steps. Here, we report the development of the "Transfer-Quench" method for measuring the rate of formation of two structural elements using a single triple-labeled mutant. This method is based on Förster resonance energy transfer combined with fluorescence quenching. We placed the donor and acceptor at the loop ends, and a quencher at an α-helical element involved in the node forming the loop. The folding of the triple-labeled mutant is monitored by the acceptor emission. The formation of nonlocal contact (loop closure) increases the time-dependent acceptor emission, while the closure of the labeled helix turn reduces this emission. The method was applied in a study of the folding mechanism of the common model protein, the B domain of staphylococcal protein A. Only natural amino acids were used as probes, and thus possible structural perturbations were minimized. Tyr and Trp residues served as donor and acceptor at the ends of a long loop between helices I and II, and a Cys residue as a quencher for the acceptor. We found that the closure of the loop (segment 14-33) occurs with the same rate constant as the nucleation of helix HII (segment 33-29), in line with the nucleation-condensation model.
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Affiliation(s)
- Gil Rahamim
- The Goodman Faculty of Life Sciences Bar Ilan University, Ramat Gan, Israel
| | - Dan Amir
- The Goodman Faculty of Life Sciences Bar Ilan University, Ramat Gan, Israel
| | - Elisha Haas
- The Goodman Faculty of Life Sciences Bar Ilan University, Ramat Gan, Israel.
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40
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Exploring the Denatured State Ensemble by Single-Molecule Chemo-Mechanical Unfolding: The Effect of Force, Temperature, and Urea. J Mol Biol 2017; 430:450-464. [PMID: 28782558 DOI: 10.1016/j.jmb.2017.07.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 07/29/2017] [Accepted: 07/31/2017] [Indexed: 11/22/2022]
Abstract
While it is widely appreciated that the denatured state of a protein is a heterogeneous conformational ensemble, there is still debate over how this ensemble changes with environmental conditions. Here, we use single-molecule chemo-mechanical unfolding, which combines force and urea using the optical tweezers, together with traditional protein unfolding studies to explore how perturbants commonly used to unfold proteins (urea, force, and temperature) affect the denatured-state ensemble. We compare the urea m-values, which report on the change in solvent accessible surface area for unfolding, to probe the denatured state as a function of force, temperature, and urea. We find that while the urea- and force-induced denatured states expose similar amounts of surface area, the denatured state at high temperature and low urea concentration is more compact. To disentangle these two effects, we use destabilizing mutations that shift the Tm and Cm. We find that the compaction of the denatured state is related to changing temperature as the different variants of acyl-coenzyme A binding protein have similar m-values when they are at the same temperature but different urea concentration. These results have important implications for protein folding and stability under different environmental conditions.
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41
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Hamadani KM, Howe J, Jensen MK, Wu P, Cate JHD, Marqusee S. An in vitro tag-and-modify protein sample generation method for single-molecule fluorescence resonance energy transfer. J Biol Chem 2017; 292:15636-15648. [PMID: 28754692 DOI: 10.1074/jbc.m117.791723] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2017] [Revised: 07/25/2017] [Indexed: 11/06/2022] Open
Abstract
Biomolecular systems exhibit many dynamic and biologically relevant properties, such as conformational fluctuations, multistep catalysis, transient interactions, folding, and allosteric structural transitions. These properties are challenging to detect and engineer using standard ensemble-based techniques. To address this drawback, single-molecule methods offer a way to access conformational distributions, transient states, and asynchronous dynamics inaccessible to these standard techniques. Fluorescence-based single-molecule approaches are parallelizable and compatible with multiplexed detection; to date, however, they have remained limited to serial screens of small protein libraries. This stems from the current absence of methods for generating either individual dual-labeled protein samples at high throughputs or protein libraries compatible with multiplexed screening platforms. Here, we demonstrate that by combining purified and reconstituted in vitro translation, quantitative unnatural amino acid incorporation via AUG codon reassignment, and copper-catalyzed azide-alkyne cycloaddition, we can overcome these challenges for target proteins that are, or can be, methionine-depleted. We present an in vitro parallelizable approach that does not require laborious target-specific purification to generate dual-labeled proteins and ribosome-nascent chain libraries suitable for single-molecule FRET-based conformational phenotyping. We demonstrate the power of this approach by tracking the effects of mutations, C-terminal extensions, and ribosomal tethering on the structure and stability of three protein model systems: barnase, spectrin, and T4 lysozyme. Importantly, dual-labeled ribosome-nascent chain libraries enable single-molecule co-localization of genotypes with phenotypes, are well suited for multiplexed single-molecule screening of protein libraries, and should enable the in vitro directed evolution of proteins with designer single-molecule conformational phenotypes of interest.
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Affiliation(s)
- Kambiz M Hamadani
- From the California Institute for Quantitative Biosciences and .,the Department of Chemistry and Biochemistry, California State University, San Marcos, California 92096, and
| | - Jesse Howe
- the Department of Chemistry and Biochemistry, California State University, San Marcos, California 92096, and
| | | | - Peng Wu
- the Department of Chemical Physiology, Scripps Research Institute, La Jolla, California 92037
| | - Jamie H D Cate
- From the California Institute for Quantitative Biosciences and .,the Departments of Molecular and Cell Biology and.,Chemistry, University of California, Berkeley, California 94720
| | - Susan Marqusee
- From the California Institute for Quantitative Biosciences and .,the Departments of Molecular and Cell Biology and
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42
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Li M, Sun T, Jin F, Yu D, Liu Z. Dimension conversion and scaling of disordered protein chains. MOLECULAR BIOSYSTEMS 2017; 12:2932-40. [PMID: 27440558 DOI: 10.1039/c6mb00415f] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
To extract protein dimension and energetics information from single-molecule fluorescence resonance energy transfer spectroscopy (smFRET) data, it is essential to establish the relationship between the distributions of the radius of gyration (Rg) and the end-to-end (donor-to-acceptor) distance (Ree). Here, we performed a coarse-grained molecular dynamics simulation to obtain a conformational ensemble of denatured proteins and intrinsically disordered proteins. For any disordered chain with fixed length, there is an excellent linear correlation between the average values of Rg and Ree under various solvent conditions, but the relationship deviates from the prediction of a Gaussian chain. A modified conversion formula was proposed to analyze smFRET data. The formula reduces the discrepancy between the results obtained from FRET and small-angle X-ray scattering (SAXS). The scaling law in a coil-globule transition process was examined where a significant finite-size effect was revealed, i.e., the scaling exponent may exceed the theoretical critical boundary [1/3, 3/5] and the prefactor changes notably during the transition. The Sanchez chain model was also tested and it was shown that the mean-field approximation works well for expanded chains.
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Affiliation(s)
- Maodong Li
- Center for Quantitative Biology, Peking University, Beijing 100871, China.
| | - Tanlin Sun
- Center for Quantitative Biology, Peking University, Beijing 100871, China.
| | - Fan Jin
- College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Daqi Yu
- College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Zhirong Liu
- Center for Quantitative Biology, Peking University, Beijing 100871, China. and College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China and Beijing National Laboratory for Molecular Sciences (BNLMS), Peking University, Beijing 100871, China
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43
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Decoupling of size and shape fluctuations in heteropolymeric sequences reconciles discrepancies in SAXS vs. FRET measurements. Proc Natl Acad Sci U S A 2017; 114:E6342-E6351. [PMID: 28716919 DOI: 10.1073/pnas.1704692114] [Citation(s) in RCA: 158] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Unfolded states of proteins and native states of intrinsically disordered proteins (IDPs) populate heterogeneous conformational ensembles in solution. The average sizes of these heterogeneous systems, quantified by the radius of gyration (RG ), can be measured by small-angle X-ray scattering (SAXS). Another parameter, the mean dye-to-dye distance (RE ) for proteins with fluorescently labeled termini, can be estimated using single-molecule Förster resonance energy transfer (smFRET). A number of studies have reported inconsistencies in inferences drawn from the two sets of measurements for the dimensions of unfolded proteins and IDPs in the absence of chemical denaturants. These differences are typically attributed to the influence of fluorescent labels used in smFRET and to the impact of high concentrations and averaging features of SAXS. By measuring the dimensions of a collection of labeled and unlabeled polypeptides using smFRET and SAXS, we directly assessed the contributions of dyes to the experimental values RG and RE For chemically denatured proteins we obtain mutual consistency in our inferences based on RG and RE , whereas for IDPs under native conditions, we find substantial deviations. Using computations, we show that discrepant inferences are neither due to methodological shortcomings of specific measurements nor due to artifacts of dyes. Instead, our analysis suggests that chemical heterogeneity in heteropolymeric systems leads to a decoupling between RE and RG that is amplified in the absence of denaturants. Therefore, joint assessments of RG and RE combined with measurements of polymer shapes should provide a consistent and complete picture of the underlying ensembles.
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Otosu T, Ishii K, Oikawa H, Arai M, Takahashi S, Tahara T. Highly Heterogeneous Nature of the Native and Unfolded States of the B Domain of Protein A Revealed by Two-Dimensional Fluorescence Lifetime Correlation Spectroscopy. J Phys Chem B 2017; 121:5463-5473. [DOI: 10.1021/acs.jpcb.7b00546] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Kunihiko Ishii
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), 2-1, Hirosawa, Wako, Saitama 351-0198, Japan
| | - Hiroyuki Oikawa
- Institute
of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1
Katahira, Aoba, Sendai, Miyagi 980-8577, Japan
| | - 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
| | - Satoshi Takahashi
- Institute
of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1
Katahira, Aoba, Sendai, Miyagi 980-8577, Japan
| | - Tahei Tahara
- Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), 2-1, Hirosawa, Wako, Saitama 351-0198, Japan
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Samanta HS, Zhuravlev PI, Hinczewski M, Hori N, Chakrabarti S, Thirumalai D. Protein collapse is encoded in the folded state architecture. SOFT MATTER 2017; 13:3622-3638. [PMID: 28447708 DOI: 10.1039/c7sm00074j] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Folded states of single domain globular proteins are compact with high packing density. The radius of gyration, Rg, of both the folded and unfolded states increase as Nν where N is the number of amino acids in the protein. The values of the Flory exponent ν are, respectively, ≈⅓ and ≈0.6 in the folded and unfolded states, coinciding with those for homopolymers. However, the extent of compaction of the unfolded state of a protein under low denaturant concentration (collapsibility), conditions favoring the formation of the folded state, is unknown. We develop a theory that uses the contact map of proteins as input to quantitatively assess collapsibility of proteins. Although collapsibility is universal, the propensity to be compact depends on the protein architecture. Application of the theory to over two thousand proteins shows that collapsibility depends not only on N but also on the contact map reflecting the native structure. A major prediction of the theory is that β-sheet proteins are far more collapsible than structures dominated by α-helices. The theory and the accompanying simulations, validating the theoretical predictions, provide insights into the differing conclusions reached using different experimental probes assessing the extent of compaction of proteins. By calculating the criterion for collapsibility as a function of protein length we provide quantitative insights into the reasons why single domain proteins are small and the physical reasons for the origin of multi-domain proteins. Collapsibility of non-coding RNA molecules is similar β-sheet proteins structures adding support to "Compactness Selection Hypothesis".
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Affiliation(s)
- Himadri S Samanta
- Department of Chemistry, University of Texas at Austin, TX 78712, USA.
| | - Pavel I Zhuravlev
- Biophysics Program, Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
| | | | - Naoto Hori
- Department of Chemistry, University of Texas at Austin, TX 78712, USA.
| | - Shaon Chakrabarti
- Biophysics Program, Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
| | - D Thirumalai
- Department of Chemistry, University of Texas at Austin, TX 78712, USA. and Biophysics Program, Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
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46
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Wallace B, Atzberger PJ. Förster resonance energy transfer: Role of diffusion of fluorophore orientation and separation in observed shifts of FRET efficiency. PLoS One 2017; 12:e0177122. [PMID: 28542211 PMCID: PMC5438121 DOI: 10.1371/journal.pone.0177122] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 04/21/2017] [Indexed: 12/14/2022] Open
Abstract
Förster resonance energy transfer (FRET) is a widely used single-molecule technique for measuring nanoscale distances from changes in the non-radiative transfer of energy between donor and acceptor fluorophores. For macromolecules and complexes this observed transfer efficiency is used to infer changes in molecular conformation under differing experimental conditions. However, sometimes shifts are observed in the FRET efficiency even when there is strong experimental evidence that the molecular conformational state is unchanged. We investigate ways in which such discrepancies can arise from kinetic effects. We show that significant shifts can arise from the interplay between excitation kinetics, orientation diffusion of fluorophores, separation diffusion of fluorophores, and non-emitting quenching.
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Affiliation(s)
- Bram Wallace
- Department of Mathematics, University of California Santa Barbara, Santa Barbara, CA, 93106, United States of America
| | - Paul J. Atzberger
- Department of Mathematics, University of California Santa Barbara, Santa Barbara, CA, 93106, United States of America
- Department of Mechanical Engineering, University of California Santa Barbara, Santa Barbara, CA, 93106, United States of America
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47
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Reddy G, Thirumalai D. Collapse Precedes Folding in Denaturant-Dependent Assembly of Ubiquitin. J Phys Chem B 2017; 121:995-1009. [DOI: 10.1021/acs.jpcb.6b13100] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Govardhan Reddy
- Solid
State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, Karnataka 560012, India
| | - D. Thirumalai
- Department
of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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48
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Kempe D, Cerminara M, Poblete S, Schöne A, Gabba M, Fitter J. Single-Molecule FRET Measurements in Additive-Enriched Aqueous Solutions. Anal Chem 2016; 89:694-702. [PMID: 27966879 DOI: 10.1021/acs.analchem.6b03147] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The addition of high amounts of chemical denaturants, salts, viscosity enhancers or macro-molecular crowding agents has an impact on the physical properties of buffer solutions. Among others, the (microscopic) viscosity, the refractive index, the dielectric constant, and the ionic strength can be affected. Here, we systematically evaluate the importance of solvent characteristics with respect to single-molecule FRET (smFRET) data. First, we present a confocal based method for the determination of fluorescence quantum yields to facilitate a fast characterization of smFRET-samples at sub-nM-concentrations. As a case study, we analyze smFRET data of structurally rigid, double-stranded DNA-oligonucleotides in aqueous buffer and in buffers with specific amounts of glycerol, guanidine hydrochloride (GdnHCl), and sodium chloride (NaCl) added. We show that the calculation of interdye distances, without taking into account solvent-induced spectral and photophysical changes of the labels, leads to deviations of up to 4 Å from the real interdye distances. Additionally, we demonstrate that electrostatic dye-dye repulsions are negligible for the interdye distance regime considered here (>50 Å). Finally, we use our approach to validate the further compaction of the already unfolded state of phosphoglycerate kinase (PGK) with decreasing denaturant concentrations, a mechanism known as coil-globule transition.
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Affiliation(s)
- Daryan Kempe
- AG Biophysik, I. Physikalisches Institut (IA), RWTH Aachen University , 52056 Aachen, Germany
| | | | | | | | | | - Jörg Fitter
- AG Biophysik, I. Physikalisches Institut (IA), RWTH Aachen University , 52056 Aachen, Germany
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49
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Zheng W, Borgia A, Buholzer K, Grishaev A, Schuler B, Best RB. Probing the Action of Chemical Denaturant on an Intrinsically Disordered Protein by Simulation and Experiment. J Am Chem Soc 2016. [PMID: 27583687 DOI: 10.1021/jacs.6b05443.probing] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2023]
Abstract
Chemical denaturants are the most commonly used agents for unfolding proteins and are thought to act by better solvating the unfolded state. Improved solvation is expected to lead to an expansion of unfolded chains with increasing denaturant concentration, providing a sensitive probe of the denaturant action. However, experiments have so far yielded qualitatively different results concerning the effects of chemical denaturation. Studies using Förster resonance energy transfer (FRET) and other methods found an increase in radius of gyration with denaturant concentration, but most small-angle X-ray scattering (SAXS) studies found no change. This discrepancy therefore challenges our understanding of denaturation mechanism and more generally the accuracy of these experiments as applied to unfolded or disordered proteins. Here, we use all-atom molecular simulations to investigate the effect of urea and guanidinium chloride on the structure of the intrinsically disordered protein ACTR, which can be studied by experiment over a wide range of denaturant concentration. Using unbiased molecular simulations with a carefully calibrated denaturant model, we find that the protein chain indeed swells with increasing denaturant concentration. This is due to the favorable association of urea or guanidinium chloride with the backbone of all residues and with the side-chains of almost all residues, with denaturant-water transfer free energies inferred from this association in reasonable accord with experimental estimates. Interactions of the denaturants with the backbone are dominated by hydrogen bonding, while interactions with side-chains include other contributions. By computing FRET efficiencies and SAXS intensities at each denaturant concentration, we show that the simulation trajectories are in accord with both experiments on this protein, demonstrating that there is no fundamental inconsistency between the two types of experiment. Agreement with experiment also supports the picture of chemical denaturation described in our simulations, driven by weak association of denaturant with the protein. Our simulations support some assumptions needed for each experiment to accurately reflect changes in protein size, namely, that the commonly used FRET chromophores do not qualitatively alter the results and that possible effects such as preferential solvent partitioning into the interior of the chain do not interfere with the determination of radius of gyration from the SAXS experiments.
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Affiliation(s)
- Wenwei Zheng
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health , Bethesda, Maryland 20892-0520, United States
| | - Alessandro Borgia
- Department of Biochemistry, University of Zurich , Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Karin Buholzer
- Department of Biochemistry, University of Zurich , Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Alexander Grishaev
- National Institute of Standards and Technology and the Institute for Bioscience and Biotechnology Research , Rockville, Maryland 20850, United States
| | - Benjamin Schuler
- Department of Biochemistry, University of Zurich , Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Robert B Best
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health , Bethesda, Maryland 20892-0520, United States
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50
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Borgia A, Zheng W, Buholzer K, Borgia MB, Schüler A, Hofmann H, Soranno A, Nettels D, Gast K, Grishaev A, Best RB, Schuler B. Consistent View of Polypeptide Chain Expansion in Chemical Denaturants from Multiple Experimental Methods. J Am Chem Soc 2016; 138:11714-26. [PMID: 27583570 PMCID: PMC5597961 DOI: 10.1021/jacs.6b05917] [Citation(s) in RCA: 142] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
There has been a long-standing controversy regarding the effect of chemical denaturants on the dimensions of unfolded and intrinsically disordered proteins: A wide range of experimental techniques suggest that polypeptide chains expand with increasing denaturant concentration, but several studies using small-angle X-ray scattering (SAXS) have reported no such increase of the radius of gyration (Rg). This inconsistency challenges our current understanding of the mechanism of chemical denaturants, which are widely employed to investigate protein folding and stability. Here, we use a combination of single-molecule Förster resonance energy transfer (FRET), SAXS, dynamic light scattering (DLS), and two-focus fluorescence correlation spectroscopy (2f-FCS) to characterize the denaturant dependence of the unfolded state of the spectrin domain R17 and the intrinsically disordered protein ACTR in two different denaturants. Standard analysis of the primary data clearly indicates an expansion of the unfolded state with increasing denaturant concentration irrespective of the protein, denaturant, or experimental method used. This is the first case in which SAXS and FRET have yielded even qualitatively consistent results regarding expansion in denaturant when applied to the same proteins. To more directly illustrate this self-consistency, we used both SAXS and FRET data in a Bayesian procedure to refine structural ensembles representative of the observed unfolded state. This analysis demonstrates that both of these experimental probes are compatible with a common ensemble of protein configurations for each denaturant concentration. Furthermore, the resulting ensembles reproduce the trend of increasing hydrodynamic radius with denaturant concentration obtained by 2f-FCS and DLS. We were thus able to reconcile the results from all four experimental techniques quantitatively, to obtain a comprehensive structural picture of denaturant-induced unfolded state expansion, and to identify the most likely sources of earlier discrepancies.
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Affiliation(s)
- Alessandro Borgia
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Wenwei Zheng
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda 20892-0520
| | - Karin Buholzer
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Madeleine B. Borgia
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Anja Schüler
- Physical Biochemistry, University of Potsdam, 14476 Potsdam, Germany
| | - Hagen Hofmann
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Andrea Soranno
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Daniel Nettels
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Klaus Gast
- Physical Biochemistry, University of Potsdam, 14476 Potsdam, Germany
| | - Alexander Grishaev
- National Institute of Standards and Technology and the Institute for Bioscience and Biotechnology Research, University of Maryland, Rockville, MD 20850
| | - Robert B. Best
- Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda 20892-0520
| | - Benjamin Schuler
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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