1
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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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2
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Bhatia S, Krishnamoorthy G, Udgaonkar JB. Mapping Distinct Sequences of Structure Formation Differentiating Multiple Folding Pathways of a Small Protein. J Am Chem Soc 2021; 143:1447-1457. [PMID: 33430589 DOI: 10.1021/jacs.0c11097] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
To determine experimentally how the multiple folding pathways of a protein differ, in the order in which the structural parts are assembled, has been a long-standing challenge. To resolve whether structure formation during folding can progress in multiple ways, the complex folding landscape of monellin has been characterized, structurally and temporally, using the multisite time-resolved FRET methodology. After an initial heterogeneous polypeptide chain collapse, structure formation proceeds on parallel pathways. Kinetic analysis of the population evolution data across various protein segments provides a clear structural distinction between the parallel pathways. The analysis leads to a phenomenological model that describes how and when discrete segments acquire structure independently of each other in different subensembles of protein molecules. When averaged over all molecules, structure formation is seen to progress as α-helix formation, followed by core consolidation, then β-sheet formation, and last end-to-end distance compaction. Parts of the protein that are closer in the primary sequence acquire structure before parts separated by longer sequence.
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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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3
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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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4
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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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5
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Abstract
This Feature Article presents a view of the protein folding transition based on the hypothesis that Nature has built features within the sequences that enable a Shortcut to efficient folding. Nature's Shortcut is proposed to be the early establishment of a set of nonlocal weak contacts, constituting protein loops that significantly constrain regions of the collapsed disordered protein into a native-like low-resolution fluctuating topology of major sections of the backbone. Nature's establishment of this scaffold of nonlocal contacts is claimed to bypass what would otherwise be a nearly hopeless unaided search for the final three-dimensional structure in proteins longer than ∼100 amino acids. To support this main contention of the Feature Article, the loop hypothesis (LH) description of early folding events is experimentally tested with time-resolved Förster resonance energy transfer techniques for adenylate kinase, and the data are shown to be consistent with theoretical predictions from the sequential collapse model (SCM). The experimentally based LH and the theoretically founded SCM are argued to provide a unified picture of the role of nonlocal contacts as constituting Nature's Shortcut to protein folding. Importantly, the SCM is shown to reliably predict key nonlocal contacts utilizing only primary sequence information. This view on Nature's Shortcut is open to the protein community for further detailed assessment, including its practical consequences, by suitable application of advanced experimental and computational techniques.
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Affiliation(s)
| | - Elisha Haas
- The Goodman Faculty of Life Sciences , Bar-Ilan University , Ramat Gan 52900 , Israel
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6
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Lai JK, Kubelka GS, Kubelka J. Effect of Mutations on the Global and Site-Specific Stability and Folding of an Elementary Protein Structural Motif. J Phys Chem B 2018; 122:11083-11094. [PMID: 29985619 DOI: 10.1021/acs.jpcb.8b05280] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding the folding mechanism of proteins requires detailed knowledge of the roles of individual amino acid residues in stabilization of specific elements and local segments of the native structure. Recently, we have utilized the combination of circular dichroism (CD) and site-specific 13C isotopically edited infrared spectroscopy (IR) coupled with the Ising-like model for protein folding to map the thermal unfolding at the residue level of a de novo designed helix-turn-helix motif αtα. Here we use the same methodology to study how the sequence of local thermal unfolding is affected by selected mutations introduced into the most and least stable parts of the motif. Seven different mutants of αtα are screened to find substitutions with the most pronounced effects on the overall stability. Subsequently, thermal unfolding of two mutated αtα sequences is studied with site-specific resolution, using four distinct 13C isotopologues of each. The data are analyzed with the Ising-like model, which builds on a previous parametrization for the original αtα sequence and tests different ways of incorporating the amino acid substitution. We show that for both more and less stable mutants only the adjustment of all interaction parameters of the model can yield a satisfactory fit to the experimental data. The stabilizing and destabilizing mutations result, respectively, in a similar increase and decrease of the stability of all probed local segments, irrespective of their position with respect to the mutation site. Consequently, the relative order of their unfolding remains essentially unchanged. These results underline the importance of the interconnectivity of the stabilizing interaction network and cooperativity of the protein structure, which is evident even in a small motif with apparently noncooperative, heterogeneous unfolding. Overall, our findings are consistent with the native structure being the dominant factor in determining the folding mechanism, regardless of the details of its overall or local thermodynamic stabilization.
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Affiliation(s)
- Jason K Lai
- Department of Chemistry , University of Wyoming , Laramie , Wyoming 82071 , United States
| | - Ginka S Kubelka
- Department of Chemistry , University of Wyoming , Laramie , Wyoming 82071 , United States
| | - Jan Kubelka
- Department of Chemistry , University of Wyoming , Laramie , Wyoming 82071 , United States
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7
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Jacob MH, D'Souza RN, Schwarzlose T, Wang X, Huang F, Haas E, Nau WM. Method-Unifying View of Loop-Formation Kinetics in Peptide and Protein Folding. J Phys Chem B 2018; 122:4445-4456. [PMID: 29617564 DOI: 10.1021/acs.jpcb.8b00879] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Protein folding can be described as a probabilistic succession of events in which the peptide chain forms loops closed by specific amino acid residue contacts, herein referred to as loop nodes. To measure loop rates, several photophysical methods have been introduced where a pair of optically active probes is incorporated at selected chain positions and the excited probe undergoes contact quenching (CQ) upon collision with the second probe. The quenching mechanisms involved triplet-triplet energy transfer, photoinduced electron transfer, and collision-induced fluorescence quenching, where the fluorescence of Dbo, an asparagine residue conjugated to 2,3-diazabicyclo[2.2.2]octane, is quenched by tryptophan. The discrepancy between the loop rates afforded from these three CQ techniques has, however, remained unresolved. In analyzing this discrepancy, we now report two short-distance FRET methods where Dbo acts as an energy acceptor in combination with tryptophan and naphtylalanine, two donors with largely different fluorescence lifetimes of 1.3 and 33 ns, respectively. Despite the different quenching mechanisms, the rates from FRET and CQ methods were, surprisingly, of comparable magnitude. This combination of FRET and CQ data led to a unifying physical model and to the conclusion that the rate of loop formation in folding reactions varies not only with the kind and number of residues that constitute the chain but also in particular with the size and properties of the residues that constitute the loop node.
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Affiliation(s)
- Maik H Jacob
- Department of Life Sciences and Chemistry , Jacobs University Bremen , Bremen 28759 , Germany
| | - Roy N D'Souza
- Department of Life Sciences and Chemistry , Jacobs University Bremen , Bremen 28759 , Germany
| | - Thomas Schwarzlose
- Department of Life Sciences and Chemistry , Jacobs University Bremen , Bremen 28759 , Germany
| | - Xiaojuan Wang
- Center for Biotechnology and Bioengineering , China University of Petroleum , Qingdao , Shandong , China 266580
| | - Fang Huang
- Center for Biotechnology and Bioengineering , China University of Petroleum , Qingdao , Shandong , China 266580
| | - Elisha Haas
- Department of Life Science , Bar Ilan University , Ramat Gan 5290002 , Israel
| | - Werner M Nau
- Department of Life Sciences and Chemistry , Jacobs University Bremen , Bremen 28759 , Germany.,Center for Biotechnology and Bioengineering , China University of Petroleum , Qingdao , Shandong , China 266580
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8
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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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9
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Singh MI, Jain V. Identification and Characterization of an Inside-Out Folding Intermediate of T4 Phage Sliding Clamp. Biophys J 2017; 113:1738-1749. [PMID: 29045868 DOI: 10.1016/j.bpj.2017.08.043] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 08/15/2017] [Accepted: 08/28/2017] [Indexed: 10/18/2022] Open
Abstract
Protein folding process involves formation of transiently occurring intermediates that are difficult to isolate and characterize. It is both necessary and interesting to characterize the structural conformations adopted by these intermediates, also called molten globules (MG), to understand protein folding. Here, we investigated the equilibrium (un)folding intermediate state of T4 phage gene product 45 (gp45, also known as DNA polymerase processivity factor or sliding clamp) obtained during chemical denaturation. We show that gp45 undergoes substantial conformational rearrangement during unfolding and forms an expanded dry-MG. By monitoring the fluorescence of tryptophans that were strategically introduced at various sites, we demonstrate that the urea-treated molecule has its surface residues flip inside the core, and closely placed residues move farther. We were also able to isolate and purify the MG form of gp45 in native condition (i.e., nondenaturing buffer, at physiological pH and temperature); characteristics of this purified molecule substantially match with urea-treated wild-type gp45. To the best of our knowledge, this is one of the few reports that demonstrate the isolation and purification of a protein folding intermediate in native condition. We believe that our work not only allows us to dissect the process of protein folding, but will also help in the designing of folding inhibitors against sliding clamps to treat a wide variety of diseases from bacterial infection to cancer, due to the vast presence of clamps in all the domains of life.
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Affiliation(s)
- Manika Indrajit Singh
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal, Madhya Pradesh, India
| | - Vikas Jain
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal, Madhya Pradesh, India.
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10
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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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11
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Goluguri RR, Udgaonkar JB. Microsecond Rearrangements of Hydrophobic Clusters in an Initially Collapsed Globule Prime Structure Formation during the Folding of a Small Protein. J Mol Biol 2016; 428:3102-17. [PMID: 27370109 DOI: 10.1016/j.jmb.2016.06.015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 06/17/2016] [Accepted: 06/19/2016] [Indexed: 12/14/2022]
Abstract
Determining how polypeptide chain collapse initiates structure formation during protein folding is a long standing goal. It has been challenging to characterize experimentally the dynamics of the polypeptide chain, which lead to the formation of a compact kinetic molten globule (MG) in about a millisecond. In this study, the sub-millisecond events that occur early during the folding of monellin from the guanidine hydrochloride-unfolded state have been characterized using multiple fluorescence and fluorescence resonance energy transfer probes. The kinetic MG is shown to form in a noncooperative manner from the unfolded (U) state as a result of at least three different processes happening during the first millisecond of folding. Initial chain compaction completes within the first 37μs, and further compaction occurs only after structure formation commences at a few milliseconds of folding. The transient nonnative and native-like hydrophobic clusters with side chains of certain residues buried form during the initial chain collapse and the nonnative clusters quickly disassemble. Subsequently, partial chain desolvation occurs, leading to the formation of a kinetic MG. The initial chain compaction and subsequent chain rearrangement appear to be barrierless processes. The two structural rearrangements within the collapsed globule appear to prime the protein for the actual folding transition.
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Affiliation(s)
- Rama Reddy Goluguri
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India
| | - Jayant B Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India.
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12
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Maity H, Reddy G. Folding of Protein L with Implications for Collapse in the Denatured State Ensemble. J Am Chem Soc 2016; 138:2609-16. [PMID: 26835789 DOI: 10.1021/jacs.5b11300] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A fundamental question in protein folding is whether the coil to globule collapse transition occurs during the initial stages of folding (burst phase) or simultaneously with the protein folding transition. Single molecule fluorescence resonance energy transfer (FRET) and small-angle X-ray scattering (SAXS) experiments disagree on whether Protein L collapse transition occurs during the burst phase of folding. We study Protein L folding using a coarse-grained model and molecular dynamics simulations. The collapse transition in Protein L is found to be concomitant with the folding transition. In the burst phase of folding, we find that FRET experiments overestimate radius of gyration, Rg, of the protein due to the application of Gaussian polymer chain end-to-end distribution to extract Rg from the FRET efficiency. FRET experiments estimate ≈6 Å decrease in Rg when the actual decrease is ≈3 Å on guanidinium chloride denaturant dilution from 7.5 to 1 M, thereby suggesting pronounced compaction in the protein dimensions in the burst phase. The ≈3 Å decrease is close to the statistical uncertainties of the Rg data measured from SAXS experiments, which suggest no compaction, leading to a disagreement with the FRET experiments. The transition-state ensemble (TSE) structures in Protein L folding are globular and extensive in agreement with the Ψ-analysis experiments. The results support the hypothesis that the TSE of single domain proteins depends on protein topology and is not stabilized by local interactions alone.
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Affiliation(s)
- Hiranmay Maity
- Solid State and Structural Chemistry Unit, Indian Institute of Science , Bangalore, Karnataka 560012, India
| | - Govardhan Reddy
- Solid State and Structural Chemistry Unit, Indian Institute of Science , Bangalore, Karnataka 560012, India
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13
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Rahamim G, Chemerovski-Glikman M, Rahimipour S, Amir D, Haas E. Resolution of Two Sub-Populations of Conformers and Their Individual Dynamics by Time Resolved Ensemble Level FRET Measurements. PLoS One 2015; 10:e0143732. [PMID: 26699718 PMCID: PMC4689530 DOI: 10.1371/journal.pone.0143732] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 11/08/2015] [Indexed: 11/19/2022] Open
Abstract
Most active biopolymers are dynamic structures; thus, ensembles of such molecules should be characterized by distributions of intra- or intermolecular distances and their fast fluctuations. A method of choice to determine intramolecular distances is based on Förster resonance energy transfer (FRET) measurements. Major advances in such measurements were achieved by single molecule FRET measurements. Here, we show that by global analysis of the decay of the emission of both the donor and the acceptor it is also possible to resolve two sub-populations in a mixture of two ensembles of biopolymers by time resolved FRET (trFRET) measurements at the ensemble level. We show that two individual intramolecular distance distributions can be determined and characterized in terms of their individual means, full width at half maximum (FWHM), and two corresponding diffusion coefficients which reflect the rates of fast ns fluctuations within each sub-population. An important advantage of the ensemble level trFRET measurements is the ability to use low molecular weight small-sized probes and to determine nanosecond fluctuations of the distance between the probes. The limits of the possible resolution were first tested by simulation and then by preparation of mixtures of two model peptides. The first labeled polypeptide was a relatively rigid Pro7 and the second polypeptide was a flexible molecule consisting of (Gly-Ser)7 repeats. The end to end distance distributions and the diffusion coefficients of each peptide were determined. Global analysis of trFRET measurements of a series of mixtures of polypeptides recovered two end-to-end distance distributions and associated intramolecular diffusion coefficients, which were very close to those determined from each of the pure samples. This study is a proof of concept study demonstrating the power of ensemble level trFRET based methods in resolution of subpopulations in ensembles of flexible macromolecules.
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Affiliation(s)
- Gil Rahamim
- The Goodman Faculty of Life Sciences Bar Ilan University, Ramat Gan Israel 52900
| | | | - Shai Rahimipour
- Department of Chemistry, Bar-Ilan University, Ramat Gan Israel 52900
| | - Dan Amir
- The Goodman Faculty of Life Sciences Bar Ilan University, Ramat Gan Israel 52900
| | - Elisha Haas
- The Goodman Faculty of Life Sciences Bar Ilan University, Ramat Gan Israel 52900
- * E-mail:
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14
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Orevi T, Rahamim G, Amir D, Kathuria S, Bilsel O, Matthews CR, Haas E. Sequential Closure of Loop Structures Forms the Folding Nucleus during the Refolding Transition of the Escherichia coli Adenylate Kinase Molecule. Biochemistry 2015; 55:79-91. [DOI: 10.1021/acs.biochem.5b00849] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Tomer Orevi
- The
Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel 52900
| | - Gil Rahamim
- The
Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel 52900
| | - Dan Amir
- The
Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel 52900
| | - Sagar Kathuria
- Department
of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, United States
| | - Osman Bilsel
- Department
of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, United States
| | - C. Robert Matthews
- Department
of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605, United States
| | - Elisha Haas
- The
Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel 52900
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15
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Goluguri RR, Udgaonkar JB. Rise of the Helix from a Collapsed Globule during the Folding of Monellin. Biochemistry 2015; 54:5356-65. [DOI: 10.1021/acs.biochem.5b00730] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Rama Reddy Goluguri
- National Centre for Biological
Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India
| | - Jayant B. Udgaonkar
- National Centre for Biological
Sciences, Tata Institute of Fundamental Research, Bengaluru 560065, India
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16
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Czar MF, Zosel F, König I, Nettels D, Wunderlich B, Schuler B, Zarrine-Afsar A, Jockusch RA. Gas-Phase FRET Efficiency Measurements To Probe the Conformation of Mass-Selected Proteins. Anal Chem 2015; 87:7559-65. [DOI: 10.1021/acs.analchem.5b01591] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Martin F. Czar
- Department
of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - Franziska Zosel
- Biochemisches
Institut, Universität Zürich, Zürich, CH-8057, Switzerland
| | - Iwo König
- Biochemisches
Institut, Universität Zürich, Zürich, CH-8057, Switzerland
| | - Daniel Nettels
- Biochemisches
Institut, Universität Zürich, Zürich, CH-8057, Switzerland
| | - Bengt Wunderlich
- Biochemisches
Institut, Universität Zürich, Zürich, CH-8057, Switzerland
| | - Benjamin Schuler
- Biochemisches
Institut, Universität Zürich, Zürich, CH-8057, Switzerland
| | | | - Rebecca A. Jockusch
- Department
of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
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17
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Milán-Garcés EA, Thaore P, Udgaonkar JB, Puranik M. Formation of a CH−π Contact in the Core of Native Barstar during Folding. J Phys Chem B 2015; 119:2928-32. [DOI: 10.1021/jp512036p] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Erix A. Milán-Garcés
- National
Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Pallavi Thaore
- National
Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Jayant B. Udgaonkar
- National
Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Mrinalini Puranik
- Indian Institute
of Science Education and Research, Pune 411008, India
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18
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Sarkar SS, Udgaonkar JB, Krishnamoorthy G. Unfolding of a small protein proceeds via dry and wet globules and a solvated transition state. Biophys J 2014; 105:2392-402. [PMID: 24268151 DOI: 10.1016/j.bpj.2013.09.048] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Revised: 08/31/2013] [Accepted: 09/30/2013] [Indexed: 10/26/2022] Open
Abstract
Dissecting a protein unfolding process into individual steps can provide valuable information on the forces that maintain the integrity of the folded structure. Solvation of the protein core determines stability, but it is not clear when such solvation occurs during unfolding. In this study, far-UV circular dichroism measurements suggest a simplistic two-state view of the unfolding of barstar, but the use of multiple other probes brings out the complexity of the unfolding reaction. Near-UV circular dichroism measurements show that unfolding commences with the loosening of tertiary interactions in a native-like intermediate, N(∗). Fluorescence resonance energy transfer measurements show that N(∗) then expands rapidly but partially to form an early unfolding intermediate IE. Fluorescence spectral measurements indicate that both N(∗) and IE have retained native-like solvent accessibility of the core, suggesting that they are dry molten globules. Dynamic quenching measurements at the single tryptophan buried in the core suggest that the core becomes solvated only later in a late wet molten globule, IL, which precedes the unfolded form. Fluorescence anisotropy decay measurements show that tight packing around the core tryptophan is lost when IL forms. Of importance, the slowest step is unfolding of the wet molten globule and involves a solvated transition state.
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Affiliation(s)
- Saswata Sankar Sarkar
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai, India
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19
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Orevi T, Rahamim G, Hazan G, Amir D, Haas E. The loop hypothesis: contribution of early formed specific non-local interactions to the determination of protein folding pathways. Biophys Rev 2013; 5:85-98. [PMID: 28510159 DOI: 10.1007/s12551-013-0113-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 03/01/2013] [Indexed: 12/12/2022] Open
Abstract
The extremely fast and efficient folding transition (in seconds) of globular proteins led to the search for some unifying principles embedded in the physics of the folding polypeptides. Most of the proposed mechanisms highlight the role of local interactions that stabilize secondary structure elements or a folding nucleus as the starting point of the folding pathways, i.e., a "bottom-up" mechanism. Non-local interactions were assumed either to stabilize the nucleus or lead to the later steps of coalescence of the secondary structure elements. An alternative mechanism was proposed, an "up-down" mechanism in which it was assumed that folding starts with the formation of very few non-local interactions which form closed long loops at the initiation of folding. The possible biological advantage of this mechanism, the "loop hypothesis", is that the hydrophobic collapse is associated with ordered compactization which reduces the chance for degradation and misfolding. In the present review the experiments, simulations and theoretical consideration that either directly or indirectly support this mechanism are summarized. It is argued that experiments monitoring the time-dependent development of the formation of specifically targeted early-formed sub-domain structural elements, either long loops or secondary structure elements, are necessary. This can be achieved by the time-resolved FRET-based "double kinetics" method in combination with mutational studies. Yet, attempts to improve the time resolution of the folding initiation should be extended down to the sub-microsecond time regime in order to design experiments that would resolve the classes of proteins which first fold by local or non-local interactions.
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Affiliation(s)
- Tomer Orevi
- The Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel, 52900
| | - Gil Rahamim
- The Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel, 52900
| | - Gershon Hazan
- The Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel, 52900
| | - Dan Amir
- The Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel, 52900
| | - Elisha Haas
- The Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel, 52900.
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20
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Nwamba CO, Chilaka FC, Moosavi-Movahedi AA. Cation modulation of hemoglobin interaction with sodium n-dodecyl sulfate (SDS). III: Calcium interaction with R- and mixed spin states of hemoglobin S at pH 5.0: the musical chair paradox. Cell Biochem Biophys 2013; 67:547-55. [PMID: 23456537 DOI: 10.1007/s12013-013-9540-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We investigate the interaction of Ca(2+) (0-500 µM) and a membrane mimic (0.60 mM SDS) with both the R- and mixed spin states hemoglobin S (HbS) as a function of time. These interactions were carried out at pH 5.0. We aim at ascertaining if there is or are differences in the UV-Visible spectra of such interactions to account for the dynamics of calcium ion concentrations [Ca(2+)] in initiating structures which may ultimately suggest HbS polymerization and or resistance to Plasmodium attack. From our results, we conclude that (a) simultaneous interaction of 40 µM Ca(2+) and 0.60 mM SDS with the R state protein would promote structural formations that can "lock up" the protein for nucleation on the membranes and or become cytotoxic to the parasite; (b) simultaneous R state HbS-SDS or R state HbS-Ca(2+) would lead to enhanced hemin formation and less deoxyHb species. This condition is unlikely to precipitate polymerization in the HbS but the resulting hemin would poison the parasite; (c) the mixed spin state HbS-SDS and 40 µM Ca(2+) interaction yields more toxic products to that of the interaction of the mixed spin HbS-SDS with 500 µM Ca(2+) thus suggesting why the 40 µM Ca(2+) is important in parasite Hb proteolysis; and (d) pronounced structural changes on interaction with SDS and Ca(2+) are more in the R state to the mixed spin state.
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Affiliation(s)
- Charles O Nwamba
- Department of Chemistry, University of Idaho, 875 Perimeter Dr. MS 2343, Moscow, ID, 83844-2343, USA,
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21
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Udgaonkar JB. Polypeptide chain collapse and protein folding. Arch Biochem Biophys 2013; 531:24-33. [DOI: 10.1016/j.abb.2012.10.003] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Revised: 10/01/2012] [Accepted: 10/08/2012] [Indexed: 12/11/2022]
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22
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Jacob MH, Dsouza RN, Ghosh I, Norouzy A, Schwarzlose T, Nau WM. Diffusion-Enhanced Förster Resonance Energy Transfer and the Effects of External Quenchers and the Donor Quantum Yield. J Phys Chem B 2012; 117:185-98. [DOI: 10.1021/jp310381f] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Maik H. Jacob
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759, Bremen, Germany
| | - Roy N. Dsouza
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759, Bremen, Germany
| | - Indrajit Ghosh
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759, Bremen, Germany
| | - Amir Norouzy
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759, Bremen, Germany
| | - Thomas Schwarzlose
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759, Bremen, Germany
| | - Werner M. Nau
- School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759, Bremen, Germany
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23
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Dasgupta A, Udgaonkar JB. Transient Non-Native Burial of a Trp Residue Occurs Initially during the Unfolding of a SH3 Domain. Biochemistry 2012; 51:8226-34. [DOI: 10.1021/bi3008627] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Amrita Dasgupta
- National Centre for Biological
Sciences, Tata Institute of Fundamental Research, Bangalore 560065,
India
| | - Jayant B. Udgaonkar
- National Centre for Biological
Sciences, Tata Institute of Fundamental Research, Bangalore 560065,
India
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24
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Dasgupta A, Udgaonkar JB. Four-State Folding of a SH3 Domain: Salt-Induced Modulation of the Stabilities of the Intermediates and Native State. Biochemistry 2012; 51:4723-34. [DOI: 10.1021/bi300223b] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Amrita Dasgupta
- National Centre for Biological
Sciences, Tata Institute of Fundamental Research, Bangalore 560065,
India
| | - Jayant B. Udgaonkar
- National Centre for Biological
Sciences, Tata Institute of Fundamental Research, Bangalore 560065,
India
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25
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Haldar S, Chattopadhyay K. Interconnection of salt-induced hydrophobic compaction and secondary structure formation depends on solution conditions: revisiting early events of protein folding at single molecule resolution. J Biol Chem 2012; 287:11546-55. [PMID: 22303014 DOI: 10.1074/jbc.m111.315648] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
What happens in the early stage of protein folding remains an interesting unsolved problem. Rapid kinetics measurements with cytochrome c using submillisecond continuous flow mixing devices suggest simultaneous formation of a compact collapsed state and secondary structure. These data seem to indicate that collapse formation is guided by specific short and long range interactions (heteropolymer collapse). A contrasting interpretation also has been proposed, which suggests that the collapse formation is rapid, nonspecific, and a trivial solvent related compaction, which could as well be observed by a homopolymer (homopolymer collapse). We address this controversy using fluorescence correlation spectroscopy (FCS), which enables us to monitor the salt-induced compaction accompanying collapse formation and the associated time constant directly at single molecule resolution. In addition, we follow the formation of secondary structure using far UV CD. The data presented here suggest that both these models (homopolymer and heteropolymer) could be applicable depending on the solution conditions. For example, the formation of secondary structure and compact state is not simultaneous in aqueous buffer. In aqueous buffer, formation of the compact state occurs through a two-state co-operative transition following heteropolymer formalism, whereas secondary structure formation takes place gradually. In contrast, in the presence of urea, a compaction of the protein radius occurs gradually over an extended range of salt concentration following homopolymer formalism. The salt-induced compaction and the formation of secondary structure take place simultaneously in the presence of urea.
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Affiliation(s)
- Shubhasis Haldar
- Protein Folding and Dynamics Laboratory, Structural Biology and Bioinformatics Division, Indian Institute of Chemical Biology, Council for Scientific and Industrial Research, 4 Raja S.C. Mullick Rd., Kolkata 700032, India
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26
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Haran G. How, when and why proteins collapse: the relation to folding. Curr Opin Struct Biol 2011; 22:14-20. [PMID: 22104965 DOI: 10.1016/j.sbi.2011.10.005] [Citation(s) in RCA: 136] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2011] [Revised: 10/15/2011] [Accepted: 10/18/2011] [Indexed: 11/25/2022]
Abstract
Unfolded proteins under strongly denaturing conditions are highly expanded. However, when the conditions are more close to native, an unfolded protein may collapse to a compact globular structure distinct from the folded state. This transition is akin to the coil-globule transition of homopolymers. Single-molecule FRET experiments have been particularly conducive in revealing the collapsed state under conditions of coexistence with the folded state. The collapse can be even more readily observed in natively unfolded proteins. Time-resolved studies, using FRET and small-angle scattering, have shown that the collapse transition is a very fast event, probably occurring on the submicrosecond time scale. The forces driving collapse are likely to involve both hydrophobic and backbone interactions. The loss of configurational entropy during collapse makes the unfolded state less stable compared to the folded state, thus facilitating folding.
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Affiliation(s)
- Gilad Haran
- Chemical Physics Department, Weizmann Institute of Science, Rehovot 76100, Israel
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27
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Khan MKA, Rahaman H, Ahmad F. Conformation and thermodynamic stability of pre-molten and molten globule states of mammalian cytochromes-c. Metallomics 2011; 3:327-38. [DOI: 10.1039/c0mt00078g] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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28
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Dasgupta A, Udgaonkar JB. Evidence for initial non-specific polypeptide chain collapse during the refolding of the SH3 domain of PI3 kinase. J Mol Biol 2010; 403:430-45. [PMID: 20837026 DOI: 10.1016/j.jmb.2010.08.046] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2010] [Revised: 08/22/2010] [Accepted: 08/24/2010] [Indexed: 12/01/2022]
Abstract
Refolding of the SH3 domain of PI3 kinase from the guanidine hydrochloride (GdnHCl)-unfolded state has been probed with millisecond (stopped flow) and sub-millisecond (continuous flow) measurements of the change in fluorescence, circular dichroism, ANS fluorescence and three-site fluorescence resonance energy transfer (FRET) efficiency. Fluorescence measurements are unable to detect structural changes preceding the rate-limiting step of folding, whereas measurements of changes in ANS fluorescence and FRET efficiency indicate that polypeptide chain collapse precedes the major structural transition. The initial chain collapse reaction is complete within 150 μs. The collapsed form at this time possesses hydrophobic clusters to which ANS binds. Each of the three measured intra-molecular distances has contracted to an extent predicted by the dependence of the FRET signal in completely unfolded protein on denaturant concentration, indicating that contraction is non-specific. The extent of contraction of each intra-molecular distance in the collapsed product of sub-millisecond folding increases continuously with a decrease in [GdnHCl]. The gradual contraction is continuous with the gradual contraction seen in completely unfolded protein, and its dependence on [GdnHCl] is not indicative of an all-or-none collapse reaction. The dependence of the extent of contraction on [GdnHCl] was similar for the three distances, indicating that chain collapse occurs in a synchronous manner across different segments of the polypeptide chain. The sub-millisecond measurements of folding in GdnHCl were unable to determine whether hydrophobic cluster formation, probed by ANS fluorescence measurement, precedes chain contraction probed by FRET. To determine whether hydrogen bonding plays a role in initial chain collapse, folding was initiated by dilution of the urea-unfolded state. The extent of contraction of at least one intra-molecular distance in the collapsed product of sub-millisecond folding in urea is similar to that seen in GdnHCl, and the initial contraction in urea too appears to be gradual.
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Affiliation(s)
- Amrita Dasgupta
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
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29
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Pugh SD, Gell C, Smith DA, Radford SE, Brockwell DJ. Single-molecule studies of the Im7 folding landscape. J Mol Biol 2010; 398:132-45. [PMID: 20211187 PMCID: PMC2855442 DOI: 10.1016/j.jmb.2010.02.048] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2009] [Revised: 02/20/2010] [Accepted: 02/26/2010] [Indexed: 11/29/2022]
Abstract
Under appropriate conditions, the four-helical Im7 (immunity protein 7) folds from an ensemble of unfolded conformers to a highly compact native state via an on-pathway intermediate. Here, we investigate the unfolded, intermediate, and native states populated during folding using diffusion single-pair fluorescence resonance energy transfer by measuring the efficiency of energy transfer (or proximity or P ratio) between pairs of fluorophores introduced into the side chains of cysteine residues placed in the center of helices 1 and 4, 1 and 3, or 2 and 4. We show that while the native states of each variant give rise to a single narrow distribution with high P values, the distributions of the intermediates trapped at equilibrium (denoted Ieqm) are fitted by two Gaussian distributions. Modulation of the folding conditions from those that stabilize the intermediate to those that destabilize the intermediate enabled the distribution of lower P value to be assigned to the population of the unfolded ensemble in equilibrium with the intermediate state. The reduced stability of the Ieqm variants allowed analysis of the effect of denaturant concentration on the compaction and breadth of the unfolded state ensemble to be quantified from 0 to 6 M urea. Significant compaction is observed as the concentration of urea is decreased in both the presence and absence of sodium sulfate, as previously reported for a variety of proteins. In the presence of Na2SO4 in 0 M urea, the P value of the unfolded state ensemble approaches that of the native state. Concurrent with compaction, the ensemble displays increased peak width of P values, possibly reflecting a reduction in the rate of conformational exchange among iso-energetic unfolded, but compact conformations. The results provide new insights into the initial stages of folding of Im7 and suggest that the unfolded state is highly conformationally constrained at the outset of folding.
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Affiliation(s)
- Sara D Pugh
- Astbury Centre for Structural Molecular Biology, Institute of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
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30
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Jha A, Udgaonkar JB, Krishnamoorthy G. Characterization of the Heterogeneity and Specificity of Interpolypeptide Interactions in Amyloid Protofibrils by Measurement of Site-Specific Fluorescence Anisotropy Decay Kinetics. J Mol Biol 2009; 393:735-52. [DOI: 10.1016/j.jmb.2009.08.053] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2009] [Revised: 07/24/2009] [Accepted: 08/17/2009] [Indexed: 10/20/2022]
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31
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Liu P, Meng X, Qu P, Zhao XS, Wang CC. Subdomain-Specific Collapse of Denatured Staphylococcal Nuclease Revealed by Single Molecule Fluorescence Resonance Energy Transfer Measurements. J Phys Chem B 2009; 113:12030-6. [PMID: 19678648 DOI: 10.1021/jp809825x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Pengcheng Liu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China, Graduate School of the Chinese Academy of Sciences, Beijing 100049, China, Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, and Department of Chemical Biology, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Xianglan Meng
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China, Graduate School of the Chinese Academy of Sciences, Beijing 100049, China, Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, and Department of Chemical Biology, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Peng Qu
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China, Graduate School of the Chinese Academy of Sciences, Beijing 100049, China, Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, and Department of Chemical Biology, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Xin Sheng Zhao
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China, Graduate School of the Chinese Academy of Sciences, Beijing 100049, China, Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, and Department of Chemical Biology, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
| | - Chih-chen Wang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China, Graduate School of the Chinese Academy of Sciences, Beijing 100049, China, Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, and Department of Chemical Biology, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
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32
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O'Brien EP, Morrison G, Brooks BR, Thirumalai D. How accurate are polymer models in the analysis of Förster resonance energy transfer experiments on proteins? J Chem Phys 2009; 130:124903. [PMID: 19334885 DOI: 10.1063/1.3082151] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Single molecule Förster resonance energy transfer (FRET) experiments are used to infer the properties of the denatured state ensemble (DSE) of proteins. From the measured average FRET efficiency, <E>, the distance distribution P(R) is inferred by assuming that the DSE can be described as a polymer. The single parameter in the appropriate polymer model (Gaussian chain, wormlike chain, or self-avoiding walk) for P(R) is determined by equating the calculated and measured <E>. In order to assess the accuracy of this "standard procedure," we consider the generalized Rouse model (GRM), whose properties [<E> and P(R)] can be analytically computed, and the Molecular Transfer Model for protein L for which accurate simulations can be carried out as a function of guanadinium hydrochloride (GdmCl) concentration. Using the precisely computed <E> for the GRM and protein L, we infer P(R) using the standard procedure. We find that the mean end-to-end distance can be accurately inferred (less than 10% relative error) using <E> and polymer models for P(R). However, the value extracted for the radius of gyration (R(g)) and the persistence length (l(p)) are less accurate. For protein L, the errors in the inferred properties increase as the GdmCl concentration increases for all polymer models. The relative error in the inferred R(g) and l(p), with respect to the exact values, can be as large as 25% at the highest GdmCl concentration. We propose a self-consistency test, requiring measurements of <E> by attaching dyes to different residues in the protein, to assess the validity of describing DSE using the Gaussian model. Application of the self-consistency test to the GRM shows that even for this simple model, which exhibits an order-->disorder transition, the Gaussian P(R) is inadequate. Analysis of experimental data of FRET efficiencies with dyes at several locations for the cold shock protein, and simulations results for protein L, for which accurate FRET efficiencies between various locations were computed, shows that at high GdmCl concentrations there are significant deviations in the DSE P(R) from the Gaussian model.
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Affiliation(s)
- Edward P O'Brien
- Biophysics Program, University of Maryland, College Park, Maryland 20742, USA
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33
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Candel AM, Cobos ES, Conejero-Lara F, Martinez JC. Evaluation of folding co-operativity of a chimeric protein based on the molecular recognition between polyproline ligands and SH3 domains. Protein Eng Des Sel 2009; 22:597-606. [PMID: 19617233 DOI: 10.1093/protein/gzp041] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
In previous work, we designed a chimeric protein, named SPCp41, to evaluate the thermodynamics of the interaction between SH3 domains and proline-rich ligands by combining thermal unfolding measurements and mutagenesis. Here, we have investigated the energetic integrity of the chain extension corresponding to the ligand sequence into the native structure, since the opposite will produce changes in the folding mechanism of the SH3 domain that may give rise to undesirable contributions to the thermodynamic parameters. We have analysed the folding-unfolding kinetics under standard conditions (50 mM phosphate pH 7). Kinetic evolutions are well described by a bi-exponential where, on top of the main kinetic phase, a low-populated slower phase appears as a consequence of cis-trans isomerisation of Pro39, as demonstrated by the influence of prolyl isomerases and by mutational analysis. There is also a burst phase possibly due to a productive formation of some helical ensembles. The main evolution, accounting for the true folding kinetics of SPCp41, can be considered as a two-state process, where the folding transition state produces essentially the same picture shown by the circular permutant S19-P20s (the 'nucleus' of the design) and the ligand will dock at the latter stages of the two-state process. Thus, all conclusions argue in favour of the effectiveness of SPCp41 to study energetic, dynamic and structural aspects of SH3-ligand interactions.
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Affiliation(s)
- Adela M Candel
- Departamento de Quimica Fisica e Instituto de Biotecnologia, Facultad de Ciencias, Universidad de Granada, Granada, Spain
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34
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Direct evidence for a dry molten globule intermediate during the unfolding of a small protein. Proc Natl Acad Sci U S A 2009; 106:12289-94. [PMID: 19617531 DOI: 10.1073/pnas.0905744106] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Little is known about how proteins begin to unfold. In particular, how and when water molecules penetrate into the protein interior during unfolding, thereby enabling the dissolution of specific structure, is poorly understood. The hypothesis that the native state expands initially into a dry molten globule, in which tight packing interactions are broken, but whose hydrophobic core has not expanded sufficiently to be able to absorb water molecules, has very little experimental support. Here, we report our analysis of the earliest observable events during the unfolding of single chain monellin (MNEI), a small plant protein. Far- and near-UV circular dichroism measurements of GdnHCl-induced unfolding indicate that a molten globule intermediate forms initially, before the major slow unfolding reaction commences. Steady-state fluorescence resonance energy transfer measurements show that the C-terminal end of the single helix of MNEI initially moves rapidly away from the single tryptophan residue that is close to the N-terminal end of the helix. The average end-to-end distance of the protein also expands during unfolding to the molten globule intermediate. At this time, water has yet to penetrate the protein core, according to the evidence from intrinsic tryptophan fluorescence and 8-anilino-1-naphthalenesulfonic acid fluorescence-monitored kinetic unfolding measurements. Our results therefore provide direct evidence for a dry molten globule intermediate at the initial stage of unfolding. Our results further suggest that the structural transition between the native and dry molten globule states could be an all-or-none transition, whereas further swelling of the globule appears to occur gradually.
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Abstract
The coil-globule transition, a tenet of the physics of polymers, has been identified in recent years as an important unresolved aspect of the initial stages of the folding of proteins. We describe the basics of the collapse transition, starting with homopolymers and continuing with proteins. Studies of denatured-state collapse under equilibrium are then presented. An emphasis is placed on single-molecule fluorescence experiments, which are particularly useful for measuring properties of the denatured state even under conditions of coexistence with the folded state. Attempts to understand the dynamics of collapse, both theoretically and experimentally, are then described. Only an upper limit for the rate of collapse has been obtained so far. Improvements in experimental and theoretical methodology are likely to continue to push our understanding of the importance of the denatured-state thermodynamics and dynamics for protein folding in the coming years.
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Affiliation(s)
- Guy Ziv
- Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot, Israel. E-mail:
| | - D. Thirumalai
- Biophysics Program, Institute for Physical Science and Technology and Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA
| | - Gilad Haran
- Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot, Israel. E-mail:
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36
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Orevi T, Ben Ishay E, Pirchi M, Jacob MH, Amir D, Haas E. Early closure of a long loop in the refolding of adenylate kinase: a possible key role of non-local interactions in the initial folding steps. J Mol Biol 2008; 385:1230-42. [PMID: 19013178 DOI: 10.1016/j.jmb.2008.10.077] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2008] [Revised: 09/16/2008] [Accepted: 10/27/2008] [Indexed: 11/25/2022]
Abstract
Most globular protein chains, when transferred from high to low denaturant concentrations, collapse instantly before they refold to their native state. The initial compaction of the protein molecule is assumed to have a key effect on the folding pathway, but it is not known whether the earliest structures formed during or instantly after collapse are defined by local or by non-local interactions--that is, by secondary structural elements or by loop closure of long segments of the protein chain. Stable closure of one or several long loops can reduce the chain entropy at a very early stage and can prevent the protein from following non-productive pathways whose number grows exponentially with the length of the protein chain. In Escherichia coli adenylate kinase (AK), about seven long loops define the topology of the native structure. We selected four loop-forming sections of the chain and probed the time course of loop formation during refolding of AK. We labeled the termini of the loop segments with tryptophan and cysteine-5-amidosalicylic acid. This donor-acceptor pair of probes used with fluorescence resonance excitation energy transfer spectroscopy (FRET) is suitable for detecting very short distances and thus is able to distinguish between random and specific compactions. Refolding of AK was initiated by stopped-flow mixing, followed simultaneously by donor and acceptor fluorescence, and analyzed in terms of energy transfer efficiency and distance. In the collapsed state of AK, observed after the 5-ms dead time of the instrument, one of the selected segments shows a native-like separation of its termini; it forms a loop already in the collapsed state. A second segment that includes the first but is longer by 15 residues shows an almost native-like separation of its termini. In contrast, a segment that is shorter but part of the second segment shows a distance separation of its termini as high as a segment that spans almost the whole protein chain. We conclude that a specific network of non-local interactions, the closure of one or several loops, can play an important role in determining the protein folding pathway at its early phases.
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Affiliation(s)
- Tomer Orevi
- The E. Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat Gan 52900, Israel
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37
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Abstract
We seek to understand the link between protein thermodynamics and protein structure in molecular detail. A classical approach to this problem involves assessing changes in protein stability resulting from added cosolvents. Under any given conditions, protein molecules in aqueous buffer are in equilibrium between unfolded and folded states, U(nfolded) <==> N(ative). Addition of organic osmolytes, small uncharged compounds found throughout nature, shift this equilibrium. Urea, a denaturing osmolyte, shifts the equilibrium toward U; trimethylamine N-oxide (TMAO), a protecting osmolyte, shifts the equilibrium toward N. Using the Tanford Transfer Model, the thermodynamic response to many such osmolytes has been dissected into groupwise free energy contributions. It is found that the energetics involving backbone hydrogen bonding controls these shifts in protein stability almost entirely, with osmolyte cosolvents simply dialing between solvent-backbone versus backbone-backbone hydrogen bonds, as a function of solvent quality. This reciprocal relationship establishes the essential link between protein thermodynamics and the protein's hydrogen-bonded backbone structure.
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Affiliation(s)
- D Wayne Bolen
- Department of Biochemistry and Molecular Biology and The Sealy Center for Structural Biology, The University of Texas Medical Branch, Galveston, TX 77555-1052, USA.
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38
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Abstract
Experimental studies show that many proteins fold along sequential pathways defined by folding intermediates. An intermediate may not always be a single population of molecules but may consist of subpopulations that differ in their average structure. These subpopulations are likely to fold via independent pathways. Parallel folding and unfolding pathways appear to arise because of structural heterogeneity. For some proteins, the folding pathways can effectively switch either because different subpopulations of an intermediate get populated under different folding conditions, or because intermediates on otherwise hidden pathways get stabilized, leading to their utilization becoming discernible, or because mutations stabilize different substructures. Therefore, the same protein may fold via different pathways in different folding conditions. Multiple folding pathways make folding robust, and evolution is likely to have selected for this robustness to ensure that a protein will fold under the varying conditions prevalent in different cellular contexts.
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Affiliation(s)
- Jayant B Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India.
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Sinha KK, Udgaonkar JB. Barrierless evolution of structure during the submillisecond refolding reaction of a small protein. Proc Natl Acad Sci U S A 2008; 105:7998-8003. [PMID: 18523007 PMCID: PMC2430349 DOI: 10.1073/pnas.0803193105] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2008] [Indexed: 11/18/2022] Open
Abstract
To determine whether a protein folding reaction can occur in the absence of a dominant barrier is crucial for understanding its complexity. Here direct ultrafast kinetic measurements have been used to study the initial submillisecond (sub-ms) folding reaction of the small protein barstar. The cooperativity of the initial folding reaction has been explored by using two probes: fluorescence resonance energy transfer, through which the contraction of two intramolecular distances is measured, and the binding of 8-anilino-1-naphthalene sulfonic acid, through which the formation of hydrophobic clusters is monitored. A fast chain contraction is shown to precede the formation of hydrophobic clusters, indicating that the sub-ms folding reaction is not cooperative. The observed rate constant of the sub-ms folding reaction monitored by 8-anilino-1-naphthalene sulfonic acid fluorescence has been found to be the same in stabilizing conditions (low urea concentrations), in which specific structure is formed, and in marginally stabilizing conditions (higher urea concentrations), where virtually no structure is formed in the product of the sub-ms folding reaction. The observation that the folding rate is independent of the folding conditions suggests that the initial folding reaction occurs in the absence of a dominant free energy barrier. These results provide kinetic evidence that the formation of specific structure need not be slowed down by any significant free energy barrier during the course of a very fast protein folding reaction.
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Affiliation(s)
- Kalyan K. Sinha
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Jayant B. Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
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Hofmann H, Golbik RP, Ott M, Hübner CG, Ulbrich-Hofmann R. Coulomb Forces Control the Density of the Collapsed Unfolded State of Barstar. J Mol Biol 2008; 376:597-605. [DOI: 10.1016/j.jmb.2007.11.083] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2007] [Revised: 11/26/2007] [Accepted: 11/27/2007] [Indexed: 10/22/2022]
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Tryptophan fluorescence reveals the presence of long-range interactions in the denatured state of ribonuclease Sa. Biophys J 2007; 94:2288-96. [PMID: 18065473 DOI: 10.1529/biophysj.107.116954] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Characterizing the denatured state ensemble is crucial to understanding protein stability and the mechanism of protein folding. The aim of this research was to see if fluorescence could be used to gain new information on the denatured state ensemble. Ribonuclease Sa (RNase Sa) contains no Trp residues. We made five variants of RNase Sa by adding Trp residues at locations where they are found in other members of the microbial ribonuclease family. To better understand the protein denatured state, we also studied the fluorescence properties of the following peptides: N-acetyl-Trp-amide (NATA), N-acetyl-Ala-Trp-Ala-amide (AWA), N-acetyl-Ala-Ala-Trp-Ala-Ala-amide (AAWAA), and the five pentapeptides with the same sequence as the Trp substitution sites in RNase Sa. The major conclusions are: 1), the wavelength of maximum fluorescence intensity, lambda(max), does not differ significantly for the peptides and the denatured proteins; 2), the fluorescence intensity at lambda(max), I(F), differs significantly for the five Trp containing variants of RNase Sa; 3), the I(F) differences for the denatured proteins are mirrored in the peptides, showing that the short-range effects giving rise to the I(F) differences in the peptides are also present in the proteins; 4) the I(F) values for the denatured proteins are more than 30% greater than for the peptides, showing the presence of long-range effects in the proteins; 5), fluorescence quenching of Trp by acrylamide and iodide is more than 50% greater in the peptides than in the denatured proteins, showing that long-range effects limit the accessibility of the quenchers to the Trp side chains in the proteins; and 6), these results show that nonlocal effects in the denatured states of proteins influence Trp fluorescence and accessibility significantly.
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Jha SK, Udgaonkar JB. Exploring the Cooperativity of the Fast Folding Reaction of a Small Protein Using Pulsed Thiol Labeling and Mass Spectrometry. J Biol Chem 2007; 282:37479-91. [DOI: 10.1074/jbc.m706714200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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