1
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Bhatia S, Udgaonkar JB. Understanding the heterogeneity intrinsic to protein folding. Curr Opin Struct Biol 2024; 84:102738. [PMID: 38041993 DOI: 10.1016/j.sbi.2023.102738] [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] [Received: 09/19/2023] [Revised: 11/09/2023] [Accepted: 11/10/2023] [Indexed: 12/04/2023]
Abstract
Relating the native fold of a protein to its amino acid sequence remains a fundamental problem in biology. While computer algorithms have demonstrated recently their prowess in predicting what structure a particular amino acid sequence will fold to, an understanding of how and why a specific protein fold is achieved remains elusive. A major challenge is to define the role of conformational heterogeneity during protein folding. Recent experimental studies, utilizing time-resolved FRET, hydrogen-exchange coupled to mass spectrometry, and single-molecule force spectroscopy, often in conjunction with simulation, have begun to reveal how conformational heterogeneity evolves during folding, and whether an intermediate ensemble of defined free energy consists of different sub-populations of molecules that may differ significantly in conformation, energy and entropy.
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Affiliation(s)
- Sandhya Bhatia
- Department of Biophysics, Howard Hughes Medical Institute UT Southwestern Medical Center, Dallas 75390, United States. https://twitter.com/Sandhyabhatia_5
| | - Jayant B Udgaonkar
- Department of Biology, Indian Institute of Science Education and Research Pune, Pashan, Pune 41008, India.
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2
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Lucignano R, Spadaccini R, Merlino A, Ami D, Natalello A, Ferraro G, Picone D. Structural insights and aggregation propensity of a super-stable monellin mutant: A new potential building block for protein-based nanostructured materials. Int J Biol Macromol 2024; 254:127775. [PMID: 38287601 DOI: 10.1016/j.ijbiomac.2023.127775] [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] [Received: 08/28/2023] [Revised: 10/12/2023] [Accepted: 10/27/2023] [Indexed: 01/31/2024]
Abstract
Protein fibrillation is commonly associated with pathologic amyloidosis. However, under appropriate conditions several proteins form fibrillar structures in vitro that can be used for biotechnological applications. MNEI and its variants, firstly designed as single chain derivatives of the sweet protein monellin, are also useful models for protein fibrillary aggregation studies. In this work, we have drawn attention to a protein dubbed Mut9, already characterized as a "super stable" MNEI variant. Comparative analysis of the respective X-ray structures revealed how the substitutions present in Mut9 eliminate several unfavorable interactions and stabilize the global structure. Molecular dynamic predictions confirmed the presence of a hydrogen-bonds network in Mut9 which increases its stability, especially at neutral pH. Thioflavin-T (ThT) binding assays and Fourier transform infrared (FTIR) spectroscopy indicated that the aggregation process occurs both at acidic and neutral pH, with and without addition of NaCl, even if with a different kinetics. Accordingly, Transmission Electron Microscopy (TEM) showed a fibrillar organization of the aggregates in all the tested conditions, albeit with some differences in the quantity and in the morphology of the fibrils. Our data underline the great potential of Mut9, which combines great stability in solution with the versatile conversion into nanostructured biomaterials.
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Affiliation(s)
- Rosanna Lucignano
- Department of Chemical Sciences, University of Naples Federico II, Complesso Universitario di Monte Sant'Angelo, Via Cintia, 80126 Naples, Italy
| | - Roberta Spadaccini
- Department of Science and Technology, University of Sannio, Via de Sanctis, 82100 Benevento, Italy
| | - Antonello Merlino
- Department of Chemical Sciences, University of Naples Federico II, Complesso Universitario di Monte Sant'Angelo, Via Cintia, 80126 Naples, Italy
| | - Diletta Ami
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza, 20126 Milano, Italy
| | - Antonino Natalello
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza, 20126 Milano, Italy
| | - Giarita Ferraro
- Department of Chemical Sciences, University of Naples Federico II, Complesso Universitario di Monte Sant'Angelo, Via Cintia, 80126 Naples, Italy.
| | - Delia Picone
- Department of Chemical Sciences, University of Naples Federico II, Complesso Universitario di Monte Sant'Angelo, Via Cintia, 80126 Naples, Italy.
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3
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Kaushik A, Udgaonkar JB. Replacement of the native cis prolines by alanine leads to simplification of the complex folding mechanism of a small globular protein. Biophys J 2023; 122:3894-3908. [PMID: 37596784 PMCID: PMC10560683 DOI: 10.1016/j.bpj.2023.08.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Revised: 08/08/2023] [Accepted: 08/15/2023] [Indexed: 08/20/2023] Open
Abstract
The folding mechanism of MNEI, a single-chain variant of naturally occurring double-chain monellin, is complex, with multiple parallel refolding channels. To determine whether its folding energy landscape could be simplified, the two native cis-prolines, Pro41 and Pro93, were mutated, singly and together, to Ala. The stability of P93A was the same as that of the wild-type protein, pWT; however, P41A and P41AP93A were destabilized by ∼0.9 kcal mol-1. The effects of the mutations on the very fast, fast, slow, and very slow phases of folding were studied. They showed that heterogeneity in the unfolded state arises due to cis to trans isomerization of the Gly92-Pro93 peptide bond. The Pro41 to Ala mutation abolished the very slow phase of folding, whereas surprisingly, the Pro93 to Ala mutation abolished the very fast phase of folding. Double-jump, interrupted folding experiments indicated that two sequential trans to cis proline isomerization steps, of the Gly92-Pro93 peptide bond followed by the Arg40-Pro41 peptide bond, lead to the formation of the native state. They also revealed the accumulation of a late native-like intermediate, N∗, which differs from the native state in the isomeric status of the Arg40-Pro41 bond, as well as in a few tertiary contacts as monitored by near-UV CD measurements. The Pro to Ala mutations not only eliminated the cis to trans Pro isomerization reaction in the unfolded state, but also the two trans to cis Pro isomerization reactions during folding. By doing so, and by differentially affecting the relative stabilities of folding intermediates, the mutations resulted in a simplification of the folding mechanism. The two Pro to Ala mutations together accelerate folding to such an extent that the native state forms more than 1000-fold faster than in the case of pWT.
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Affiliation(s)
- Anushka Kaushik
- Indian Institute of Science Education and Research, Pune, India
| | - Jayant B Udgaonkar
- Indian Institute of Science Education and Research, Pune, India; National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bengaluru, India.
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4
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Bhattacharjee R, Udgaonkar JB. Differentiating between the sequence of structural events on alternative pathways of folding of a heterodimeric protein. Protein Sci 2022; 31:e4513. [PMID: 36382901 PMCID: PMC9703597 DOI: 10.1002/pro.4513] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 11/09/2022] [Accepted: 11/10/2022] [Indexed: 11/17/2022]
Abstract
Distinguishing between competing pathways of folding of a protein, on the basis of how they differ in their progress of structure acquisition, remains an important challenge in protein folding studies. A previous study had shown that the heterodimeric protein, double chain monellin (dcMN) switches between alternative folding pathways upon a change in guanidine hydrochloride (GdnHCl) concentration. In the current study, the folding of dcMN has been characterized by the pulsed hydrogen exchange (HX) labeling methodology used in conjunction with mass spectrometry. Quantification of the extent to which folding intermediates accumulate and then disappear with time of folding at both low and high GdnHCl concentrations, where the folding pathways are known to be different, shows that the folding mechanism is describable by a triangular three-state mechanism. Structural characterization of the productive folding intermediates populated on the alternative pathways has enabled the pathways to be differentiated on the basis of the progress of structure acquisition that occurs on them. The intermediates on the two pathways differ in the extent to which the α-helix and the rest of the β-sheet have acquired structure that is protective against HX. The major difference is, however, that β2 has not acquired any protective structure in the intermediate formed on one pathway, but it has acquired significant protective structure in the intermediate formed on the alternative pathway. Hence, the sequence of structural events is different on the two alternative pathways.
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Affiliation(s)
- Rupam Bhattacharjee
- National Centre for Biological Sciences, Tata Institute of Fundamental ResearchBengaluruKarnatakaIndia
- Indian Institute of Science Education and ResearchPuneMaharashtraIndia
| | - Jayant B. Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental ResearchBengaluruKarnatakaIndia
- Indian Institute of Science Education and ResearchPuneMaharashtraIndia
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5
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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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6
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Bhattacharjee R, Udgaonkar JB. Structural Characterization of the Cooperativity of Unfolding of a Heterodimeric Protein using Hydrogen Exchange-Mass Spectrometry. J Mol Biol 2021; 433:167268. [PMID: 34563547 DOI: 10.1016/j.jmb.2021.167268] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Revised: 09/03/2021] [Accepted: 09/16/2021] [Indexed: 10/20/2022]
Abstract
Little is known about how the sequence of structural changes in one chain of a heterodimeric protein is coupled to those in the other chain during protein folding and unfolding reactions, and whether individual secondary structural changes in the two chains occur in one or many coordinated steps. Here, the unfolding mechanism of a small heterodimeric protein, double chain monellin, has been characterized using hydrogen exchange-mass spectrometry. Transient structure opening, which enables HX, was found to be describable by a five state N ↔ I1 ↔ I2 ↔ I3 ↔ U mechanism. Structural changes occur gradually in the first three steps, and cooperatively in the last step. β strands 2, 4 and 5, as well as the α-helix undergo transient unfolding during all three non-cooperative steps, while β1 and the two loops on both sides of the helix undergo transient unfolding during the first two steps. In the absence of GdnHCl, only β3 in chain A of the protein unfolds during the last cooperative step, while in the presence of 1 M GdnHCl, not only β3, but also β2 in chain B unfolds cooperatively. Hence, the extent of cooperative structural change and size of the cooperative unfolding unit increase when the protein is destabilized by denaturant. The naturally evolved two-chain variant of monellin folds and unfolds in a more cooperative manner than does a single chain variant created artificially, suggesting that increasing folding cooperativity, even at the cost of decreasing stability, may be a driving force in the evolution of proteins.
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Affiliation(s)
- Rupam Bhattacharjee
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India; Indian Institute of Science Education and Research, Pune, India. https://twitter.com/Rupam_B01
| | - Jayant B Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India; Indian Institute of Science Education and Research, Pune, India.
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7
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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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8
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Delfi M, Leone S, Emendato A, Ami D, Borriello M, Natalello A, Iannuzzi C, Picone D. Understanding the self-assembly pathways of a single chain variant of monellin: A first step towards the design of sweet nanomaterials. Int J Biol Macromol 2020; 152:21-29. [PMID: 32088237 DOI: 10.1016/j.ijbiomac.2020.02.229] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Revised: 02/19/2020] [Accepted: 02/20/2020] [Indexed: 12/20/2022]
Abstract
Peptides and proteins possess an inherent tendency to self-assemble, prompting the formation of amyloid aggregates from their soluble and functional states. Amyloids are linked to many devastating diseases, but self-assembling proteins can also represent formidable tools to produce new and sustainable biomaterials for biomedical and biotechnological applications. The mechanism of fibrillar aggregation, which influences the morphology and the properties of the protein aggregates, depend on factors such as pH, ionic strength, temperature, agitation, and protein concentration. We have here used intensive mechanical agitation, with or without beads, to prompt the aggregation of the single-chain derivative of the plant protein monellin, named MNEI, which is a well characterized sweet protein. Transmission electron microscopy confirmed the formation of fibrils several micrometers long, morphologically different from the previously characterized fibers of MNEI. Changes in the protein secondary structures during the aggregation process were monitored by Fourier transform infrared spectroscopy, which detected differences in the conformation of the final aggregates obtained under mechanical agitation. Moreover, soluble oligomers could be detected in the early phases of aggregation by polyacrylamide gel-electrophoresis. These findings emphasize the existence of multiple pathways of fibrillar aggregation for MNEI, which could be exploited for the design of innovative protein-based biomaterials.
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Affiliation(s)
- Masoud Delfi
- Department of Chemical Sciences, University of Naples "Federico II", Complesso Universitario Monte S. Angelo, Via Cintia, 80126 Napoli, Italy
| | - Serena Leone
- Department of Chemical Sciences, University of Naples "Federico II", Complesso Universitario Monte S. Angelo, Via Cintia, 80126 Napoli, Italy
| | - Alessandro Emendato
- Department of Chemical Sciences, University of Naples "Federico II", Complesso Universitario Monte S. Angelo, Via Cintia, 80126 Napoli, Italy
| | - Diletta Ami
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milano, Italy
| | - Margherita Borriello
- Department of Precision Medicine, University of Campania "L. Vanvitelli", Via L. De Crecchio 7, 80138 Naples, Italy
| | - Antonino Natalello
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milano, Italy
| | - Clara Iannuzzi
- Department of Precision Medicine, University of Campania "L. Vanvitelli", Via L. De Crecchio 7, 80138 Naples, Italy.
| | - Delia Picone
- Department of Chemical Sciences, University of Naples "Federico II", Complesso Universitario Monte S. Angelo, Via Cintia, 80126 Napoli, Italy.
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9
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Donnarumma F, Leone S, Delfi M, Emendato A, Ami D, Laurents DV, Natalello A, Spadaccini R, Picone D. Probing structural changes during amyloid aggregation of the sweet protein MNEI. FEBS J 2019; 287:2808-2822. [DOI: 10.1111/febs.15168] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Revised: 11/20/2019] [Accepted: 12/05/2019] [Indexed: 12/13/2022]
Affiliation(s)
- Federica Donnarumma
- Department of Chemical Sciences University of Naples ‘Federico II’ Napoli Italy
| | - Serena Leone
- Department of Chemical Sciences University of Naples ‘Federico II’ Napoli Italy
| | - Masoud Delfi
- Department of Chemical Sciences University of Naples ‘Federico II’ Napoli Italy
| | - Alessandro Emendato
- Department of Chemical Sciences University of Naples ‘Federico II’ Napoli Italy
| | - Diletta Ami
- Department of Biotechnology and Biosciences University of Milano‐Bicocca Italy
| | - Douglas V. Laurents
- Institute of Physical Chemistry ‘Rocasolano’ Consejo Superior de Investigaciones Científicas Madrid Spain
| | - Antonino Natalello
- Department of Biotechnology and Biosciences University of Milano‐Bicocca Italy
| | - Roberta Spadaccini
- Department of Science and Technology Università degli Studi del Sannio Benevento Italy
| | - Delia Picone
- Department of Chemical Sciences University of Naples ‘Federico II’ Napoli Italy
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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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PFDB: A standardized protein folding database with temperature correction. Sci Rep 2019; 9:1588. [PMID: 30733462 PMCID: PMC6367381 DOI: 10.1038/s41598-018-36992-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 11/22/2018] [Indexed: 11/23/2022] Open
Abstract
We constructed a standardized protein folding kinetics database (PFDB) in which the logarithmic rate constants of all listed proteins are calculated at the standard temperature (25 °C). A temperature correction based on the Eyring–Kramers equation was introduced for proteins whose folding kinetics were originally measured at temperatures other than 25 °C. We verified the temperature correction by comparing the logarithmic rate constants predicted and experimentally observed at 25 °C for 14 different proteins, and the results demonstrated improvement of the quality of the database. PFDB consists of 141 (89 two-state and 52 non-two-state) single-domain globular proteins, which has the largest number among the currently available databases of protein folding kinetics. PFDB is thus intended to be used as a standard for developing and testing future predictive and theoretical studies of protein folding. PFDB can be accessed from the following link: http://lee.kias.re.kr/~bala/PFDB.
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12
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Dahiya V, Buchner J. Functional principles and regulation of molecular chaperones. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2018; 114:1-60. [PMID: 30635079 DOI: 10.1016/bs.apcsb.2018.10.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
To be able to perform their biological function, a protein needs to be correctly folded into its three dimensional structure. The protein folding process is spontaneous and does not require the input of energy. However, in the crowded cellular environment where there is high risk of inter-molecular interactions that may lead to protein molecules sticking to each other, hence forming aggregates, protein folding is assisted. Cells have evolved robust machinery called molecular chaperones to deal with the protein folding problem and to maintain proteins in their functional state. Molecular chaperones promote efficient folding of newly synthesized proteins, prevent their aggregation and ensure protein homeostasis in cells. There are different classes of molecular chaperones functioning in a complex interplay. In this review, we discuss the principal characteristics of different classes of molecular chaperones, their structure-function relationships, their mode of regulation and their involvement in human disorders.
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Affiliation(s)
- Vinay Dahiya
- Center for Integrated Protein Science Munich CIPSM at the Department Chemie, Technische Universität München, Garching, Germany
| | - Johannes Buchner
- Center for Integrated Protein Science Munich CIPSM at the Department Chemie, Technische Universität München, Garching, Germany.
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14
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pH driven fibrillar aggregation of the super-sweet protein Y65R-MNEI: A step-by-step structural analysis. Biochim Biophys Acta Gen Subj 2018; 1862:808-815. [DOI: 10.1016/j.bbagen.2017.12.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Revised: 12/14/2017] [Accepted: 12/22/2017] [Indexed: 11/22/2022]
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15
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Mascarenhas NM, Terse VL, Gosavi S. Intrinsic Disorder in a Well-Folded Globular Protein. J Phys Chem B 2018; 122:1876-1884. [PMID: 29304275 DOI: 10.1021/acs.jpcb.7b12546] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The folded structure of the heterodimeric sweet protein monellin mimics single-chain proteins with topology β1-α1-β2-β3-β4-β5 (chain A: β3-β4-β5; chain B: β1-α1-β2). Furthermore, like naturally occurring single-chain proteins of a similar size, monellin folds cooperatively with no detectable intermediates. However, the two monellin chains, A and B, are marginally structured in isolation and fold only upon binding to each other. Thus, monellin presents a unique opportunity to understand the design of intrinsically disordered proteins that fold upon binding. Here, we study the folding of a single-chain variant of monellin (scMn) using simulations of an all heavy-atom structure-based model. These simulations can explain mechanistic details derived from scMn experiments performed using several different structural probes. scMn folds cooperatively in our structure-based simulations, as is also seen in experiments. We find that structure formation near the transition-state ensemble of scMn is not uniformly distributed but is localized to a hairpin-like structure which contains one strand from each chain (β2, β3). Thus, the sequence and the underlying energetics of heterodimeric monellin promote the early formation of the interchain interface (β2-β3). By studying computational scMn mutants whose "interchain" interactions are deleted, we infer that this energy distribution allows the two protein chains to remain largely disordered when this interface is not folded. From these results, we suggest that cutting the protein backbone of a globular protein between residues which lie within its folding nucleus may be one way to construct two disordered fragments which fold upon binding.
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Affiliation(s)
| | - Vishram L Terse
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research , Bangalore 560065, India
| | - Shachi Gosavi
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research , Bangalore 560065, India
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16
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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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17
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Bhatia S, Krishnamoorthy G, Udgaonkar JB. Site-specific time-resolved FRET reveals local variations in the unfolding mechanism in an apparently two-state protein unfolding transition. Phys Chem Chem Phys 2018; 20:3216-3232. [DOI: 10.1039/c7cp06214a] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Using multi-site time-resolved FRET, it is shown that equilibrium unfolding of monellin is not only heterogeneous, but that the degree of non-cooperativity differs between the sole α-helix and different parts of the β-sheet.
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Affiliation(s)
- Sandhya Bhatia
- 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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18
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Malhotra P, Jethva PN, Udgaonkar JB. Chemical Denaturants Smoothen Ruggedness on the Free Energy Landscape of Protein Folding. Biochemistry 2017; 56:4053-4063. [DOI: 10.1021/acs.biochem.7b00367] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Pooja Malhotra
- National Centre for Biological Sciences, Tata Institute
of Fundamental Research, Bengaluru 560065, India
| | - Prashant N. Jethva
- 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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19
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Mascarenhas NM, Gosavi S. Understanding protein domain-swapping using structure-based models of protein folding. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2016; 128:113-120. [PMID: 27867057 PMCID: PMC7127520 DOI: 10.1016/j.pbiomolbio.2016.09.013] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/23/2016] [Revised: 09/05/2016] [Accepted: 09/26/2016] [Indexed: 02/05/2023]
Abstract
In domain-swapping, two or more identical protein monomers exchange structural elements and fold into dimers or multimers whose units are structurally similar to the original monomer. Domain-swapping is of biotechnological interest because inhibiting domain-swapping can reduce disease-causing fibrillar protein aggregation. To achieve such inhibition, it is important to understand both the energetics that stabilize the domain-swapped structure and the protein dynamics that enable the swapping. Structure-based models (SBMs) encode the folded structure of the protein in their potential energy functions. SBMs have been successfully used to understand diverse aspects of monomer folding. Symmetrized SBMs model interactions between two identical protein chains using only intra-monomer interactions. Molecular dynamics simulations of such symmetrized SBMs have been used to correctly predict the domain-swapped structure and to understand the mechanism of domain-swapping. Here, we review such models and illustrate that monomer topology determines key aspects of domain-swapping. However, in some proteins, specifics of local energetic interactions modulate domain-swapping and these need to be added to the symmetrized SBMs. We then summarize some general principles of the mechanism of domain-swapping that emerge from the symmetrized SBM simulations. Finally, using our own results, we explore how symmetrized SBMs could be used to design domain-swapping in proteins.
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Affiliation(s)
- Nahren Manuel Mascarenhas
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Shachi Gosavi
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India.
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20
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Malhotra P, Udgaonkar JB. How cooperative are protein folding and unfolding transitions? Protein Sci 2016; 25:1924-1941. [PMID: 27522064 PMCID: PMC5079258 DOI: 10.1002/pro.3015] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 08/09/2016] [Accepted: 08/09/2016] [Indexed: 11/12/2022]
Abstract
A thermodynamically and kinetically simple picture of protein folding envisages only two states, native (N) and unfolded (U), separated by a single activation free energy barrier, and interconverting by cooperative two-state transitions. The folding/unfolding transitions of many proteins occur, however, in multiple discrete steps associated with the formation of intermediates, which is indicative of reduced cooperativity. Furthermore, much advancement in experimental and computational approaches has demonstrated entirely non-cooperative (gradual) transitions via a continuum of states and a multitude of small energetic barriers between the N and U states of some proteins. These findings have been instrumental towards providing a structural rationale for cooperative versus noncooperative transitions, based on the coupling between interaction networks in proteins. The cooperativity inherent in a folding/unfolding reaction appears to be context dependent, and can be tuned via experimental conditions which change the stabilities of N and U. The evolution of cooperativity in protein folding transitions is linked closely to the evolution of function as well as the aggregation propensity of the protein. A large activation energy barrier in a fully cooperative transition can provide the kinetic control required to prevent the accumulation of partially unfolded forms, which may promote aggregation. Nevertheless, increasing evidence for barrier-less "downhill" folding, as well as for continuous "uphill" unfolding transitions, indicate that gradual non-cooperative processes may be ubiquitous features on the free energy landscape of protein folding.
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Affiliation(s)
- Pooja Malhotra
- 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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21
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Mascarenhas NM, Gosavi S. Protein Domain-Swapping Can Be a Consequence of Functional Residues. J Phys Chem B 2016; 120:6929-38. [PMID: 27331242 DOI: 10.1021/acs.jpcb.6b03968] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Monomer topology has been implicated in domain-swapping, a potential first step on the route to disease-causing protein aggregation. Despite having the same topology (β1-α1-β2-β3-β4-β5), the cysteine protease inhibitor stefin-B domain swaps more readily than a single-chain variant of the heterodimeric sweet protein monellin (scMn). Here, we computationally study the folding of stefin-B and scMn in order to understand the molecular basis for the difference in their domain-swapping propensities. In agreement with experiments, our structure-based simulations show that scMn folds cooperatively without the population of an intermediate while stefin-B populates an equilibrium intermediate state. Since the simulation intermediate has only one domain structured (β3-β4-β5), it can directly lead to domain-swapping. Using computational variants of stefin-B, we show that the population of this intermediate is caused by regions of stefin-B that have been implicated in protease inhibition. We also find that the protease-binding regions are located on two structural elements and localized in space. In contrast, the residues that contribute to the sweetness of monellin are not localized to a few structural elements but are distributed over the protein fold. We conclude that the distributed functional residues of monellin do not induce large local perturbations in the protein structure, eliminating the formation of folding intermediates and in turn domain-swapping. On the other hand, the localized protease-binding regions of stefin-B promote the formation of a folding intermediate which can lead to domain-swapping. Thus, domain-swapping can be a direct consequence of the constraints that function imposes on the protein structure.
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Affiliation(s)
- Nahren Manuel Mascarenhas
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research , Bangalore 560065, India
| | - Shachi Gosavi
- Simons Centre for the Study of Living Machines, National Centre for Biological Sciences, Tata Institute of Fundamental Research , Bangalore 560065, India
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22
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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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23
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Malhotra P, Udgaonkar JB. Secondary Structural Change Can Occur Diffusely and Not Modularly during Protein Folding and Unfolding Reactions. J Am Chem Soc 2016; 138:5866-78. [DOI: 10.1021/jacs.6b03356] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Pooja Malhotra
- 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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24
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Aksel T, Barrick D. Direct observation of parallel folding pathways revealed using a symmetric repeat protein system. Biophys J 2015; 107:220-32. [PMID: 24988356 DOI: 10.1016/j.bpj.2014.04.058] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2014] [Revised: 04/09/2014] [Accepted: 04/11/2014] [Indexed: 11/26/2022] Open
Abstract
Although progress has been made to determine the native fold of a polypeptide from its primary structure, the diversity of pathways that connect the unfolded and folded states has not been adequately explored. Theoretical and computational studies predict that proteins fold through parallel pathways on funneled energy landscapes, although experimental detection of pathway diversity has been challenging. Here, we exploit the high translational symmetry and the direct length variation afforded by linear repeat proteins to directly detect folding through parallel pathways. By comparing folding rates of consensus ankyrin repeat proteins (CARPs), we find a clear increase in folding rates with increasing size and repeat number, although the size of the transition states (estimated from denaturant sensitivity) remains unchanged. The increase in folding rate with chain length, as opposed to a decrease expected from typical models for globular proteins, is a clear demonstration of parallel pathways. This conclusion is not dependent on extensive curve-fitting or structural perturbation of protein structure. By globally fitting a simple parallel-Ising pathway model, we have directly measured nucleation and propagation rates in protein folding, and have quantified the fluxes along each path, providing a detailed energy landscape for folding. This finding of parallel pathways differs from results from kinetic studies of repeat-proteins composed of sequence-variable repeats, where modest repeat-to-repeat energy variation coalesces folding into a single, dominant channel. Thus, for globular proteins, which have much higher variation in local structure and topology, parallel pathways are expected to be the exception rather than the rule.
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Affiliation(s)
- Tural Aksel
- Deparment of Biochemistry, Stanford University School of Medicine, Stanford, California
| | - Doug Barrick
- T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, Maryland.
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25
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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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26
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Malhotra P, Udgaonkar JB. Tuning Cooperativity on the Free Energy Landscape of Protein Folding. Biochemistry 2015; 54:3431-41. [DOI: 10.1021/acs.biochem.5b00247] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Pooja Malhotra
- 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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27
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Malhotra P, Udgaonkar JB. High-Energy Intermediates in Protein Unfolding Characterized by Thiol Labeling under Nativelike Conditions. Biochemistry 2014; 53:3608-20. [DOI: 10.1021/bi401493t] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Pooja Malhotra
- 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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28
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Sabareesan AT, Udgaonkar JB. Amyloid Fibril Formation by the Chain B Subunit of Monellin Occurs by a Nucleation-Dependent Polymerization Mechanism. Biochemistry 2014; 53:1206-17. [DOI: 10.1021/bi401467p] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- A. T. Sabareesan
- 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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29
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Aghera N, Udgaonkar JB. The Utilization of Competing Unfolding Pathways of Monellin Is Dictated by Enthalpic Barriers. Biochemistry 2013; 52:5770-9. [DOI: 10.1021/bi400688w] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Nilesh Aghera
- 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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30
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Aghera N, Dasgupta I, Udgaonkar JB. A Buried Ionizable Residue Destabilizes the Native State and the Transition State in the Folding of Monellin. Biochemistry 2012; 51:9058-66. [DOI: 10.1021/bi3008017] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Nilesh Aghera
- National
Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065,
India
| | - Ishita 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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31
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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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32
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Aghera N, Udgaonkar JB. Kinetic Studies of the Folding of Heterodimeric Monellin: Evidence for Switching between Alternative Parallel Pathways. J Mol Biol 2012; 420:235-50. [DOI: 10.1016/j.jmb.2012.04.019] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2011] [Revised: 04/14/2012] [Accepted: 04/18/2012] [Indexed: 11/17/2022]
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33
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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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34
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Aghera N, Udgaonkar JB. Heterologous expression, purification and characterization of heterodimeric monellin. Protein Expr Purif 2011; 76:248-53. [DOI: 10.1016/j.pep.2010.11.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2010] [Revised: 10/26/2010] [Accepted: 11/03/2010] [Indexed: 11/29/2022]
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35
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Jha SK, Dasgupta A, Malhotra P, Udgaonkar JB. Identification of Multiple Folding Pathways of Monellin Using Pulsed Thiol Labeling and Mass Spectrometry. Biochemistry 2011; 50:3062-74. [DOI: 10.1021/bi1006332] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Santosh Kumar Jha
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Amrita Dasgupta
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Pooja Malhotra
- 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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36
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Aghera N, Earanna N, Udgaonkar JB. Equilibrium unfolding studies of monellin: the double-chain variant appears to be more stable than the single-chain variant. Biochemistry 2011; 50:2434-44. [PMID: 21351752 DOI: 10.1021/bi101955f] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To improve our understanding of the contributions of different stabilizing interactions to protein stability, including that of residual structure in the unfolded state, the small sweet protein monellin has been studied in both its two variant forms, the naturally occurring double-chain variant (dcMN) and the artificially created single-chain variant (scMN). Equilibrium guanidine hydrochloride-induced unfolding studies at pH 7 show that the standard free energy of unfolding, ΔG°(U), of dcMN to unfolded chains A and B and its dependence on guanidine hydrochloride (GdnHCl) concentration are both independent of protein concentration, while the midpoint of unfolding has an exponential dependence on protein concentration. Hence, the unfolding of dcMN like that of scMN can be described as two-state unfolding. The free energy of dissociation, ΔG°(d), of the two free chains, A and B, from dcMN, as measured by equilibrium binding studies, is significantly lower than ΔG°(U), apparently because of the presence of residual structure in free chain B. The value of ΔG°(U), at the standard concentration of 1 M, is found to be ∼5.5 kcal mol(-1) higher for dcMN than for scMN in the range from pH 4 to 9, over which unfolding appears to be two-state. Hence, dcMN appears to be more stable than scMN. It seems that unfolded scMN is stabilized by residual structure that is absent in unfolded dcMN and/or that native scMN is destabilized by strain that is relieved in native dcMN. The value of ΔG°(U) for both protein variants decreases with an increase in pH from 4 to 9, apparently because of the thermodynamic coupling of unfolding to the protonation of a buried carboxylate side chain whose pK(a) shifts from 4.5 in the unfolded state to 9 in the native state. Finally, it is shown that although the thermodynamic stabilities of dcMN and scMN are very different, their kinetic stabilities with respect to unfolding in GdnHCl are very similar.
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Affiliation(s)
- Nilesh Aghera
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
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37
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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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38
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Wu SJ, Luo J, O'Neil KT, Kang J, Lacy ER, Canziani G, Baker A, Huang M, Tang QM, Raju TS, Jacobs SA, Teplyakov A, Gilliland GL, Feng Y. Structure-based engineering of a monoclonal antibody for improved solubility. Protein Eng Des Sel 2010; 23:643-51. [PMID: 20543007 DOI: 10.1093/protein/gzq037] [Citation(s) in RCA: 149] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Protein aggregation is of great concern to pharmaceutical formulations and has been implicated in several diseases. We engineered an anti-IL-13 monoclonal antibody CNTO607 for improved solubility. Three structure-based engineering approaches were employed in this study: (i) modifying the isoelectric point (pI), (ii) decreasing the overall surface hydrophobicity and (iii) re-introducing an N-linked carbohydrate moiety within a complementarity-determining region (CDR) sequence. A mutant was identified with a modified pI that had a 2-fold improvement in solubility while retaining the binding affinity to IL-13. Several mutants with decreased overall surface hydrophobicity also showed moderately improved solubility while maintaining a similar antigen affinity. Structural studies combined with mutagenesis data identified an aggregation 'hot spot' in heavy-chain CDR3 (H-CDR3) that contains three residues ((99)FHW(100a)). The same residues, however, were found to be essential for high affinity binding to IL-13. On the basis of the spatial proximity and germline sequence, we reintroduced the consensus N-glycosylation site in H-CDR2 which was found in the original antibody, anticipating that the carbohydrate moiety would shield the aggregation 'hot spot' in H-CDR3 while not interfering with antigen binding. Peptide mapping and mass spectrometric analysis revealed that the N-glycosylation site was generally occupied. This variant showed greatly improved solubility and bound to IL-13 with affinity similar to CNTO607 without the N-linked carbohydrate. All three engineering approaches led to improved solubility and adding an N-linked carbohydrate to the CDR was the most effective route for enhancing the solubility of CNTO607.
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Affiliation(s)
- Sheng-Jiun Wu
- Biologics Research, Centocor R&D, 145 King of Prussia Radnor, PA 19087-4557, USA.
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39
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Different Folding Pathways Taken by Highly Homologous Proteins, Goat α-Lactalbumin and Canine Milk Lysozyme. J Mol Biol 2010; 396:1361-78. [DOI: 10.1016/j.jmb.2010.01.021] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2009] [Revised: 01/10/2010] [Accepted: 01/11/2010] [Indexed: 11/19/2022]
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40
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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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41
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Continuous dissolution of structure during the unfolding of a small protein. Proc Natl Acad Sci U S A 2009; 106:11113-8. [PMID: 19553216 DOI: 10.1073/pnas.0812564106] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The unfolding kinetics of many small proteins appears to be first order, when measured by ensemble-averaging probes such as fluorescence and circular dichroism. For one such protein, monellin, it is shown here that hidden behind this deceptive simplicity is a complexity that becomes evident with the use of experimental probes that are able to discriminate between different conformations in an ensemble of structures. In this study, the unfolding of monellin has been probed by measurement of the changes in the distributions of 4 different intramolecular distances, using a multisite, time-resolved fluorescence resonance energy transfer methodology. During the course of unfolding, the protein molecules are seen to undergo slow and continuous, diffusive swelling. The swelling process can be modeled as the slow diffusive swelling of a Rouse-like chain with some additional noncovalent, intramolecular interactions. Here, we show that specific structure is lost during the swelling process gradually, and not in an all-or-none manner, during unfolding.
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Patra AK, Udgaonkar JB. GroEL Can Unfold Late Intermediates Populated on the Folding Pathways of Monellin. J Mol Biol 2009; 389:759-75. [DOI: 10.1016/j.jmb.2009.04.039] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Revised: 04/10/2009] [Accepted: 04/20/2009] [Indexed: 10/20/2022]
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Wani AH, Udgaonkar JB. Revealing a Concealed Intermediate that Forms after the Rate-limiting Step of Refolding of the SH3 Domain of PI3 Kinase. J Mol Biol 2009; 387:348-62. [DOI: 10.1016/j.jmb.2009.01.060] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2008] [Revised: 12/25/2008] [Accepted: 01/28/2009] [Indexed: 10/21/2022]
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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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