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Bozovic O, Jankovic B, Hamm P. Using azobenzene photocontrol to set proteins in motion. Nat Rev Chem 2021; 6:112-124. [PMID: 37117294 DOI: 10.1038/s41570-021-00338-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/14/2021] [Indexed: 02/06/2023]
Abstract
Controlling the activity of proteins with azobenzene photoswitches is a potent tool for manipulating their biological function. With the help of light, it is possible to change binding affinities, control allostery or manipulate complex biological processes, for example. Additionally, owing to their intrinsically fast photoisomerization, azobenzene photoswitches can serve as triggers that initiate out-of-equilibrium processes. Such switching of the activity initiates a cascade of conformational events that can be accessed with time-resolved methods. In this Review, we show how the potency of azobenzene photoswitching can be combined with transient spectroscopic techniques to disclose the order of events and experimentally observe biomolecular interactions in real time. This strategy will further our understanding of how a protein can accommodate, adapt and readjust its structure to answer an incoming signal, revealing more of the dynamical character of proteins.
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2
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Jankovic B, Ruf J, Zanobini C, Bozovic O, Buhrke D, Hamm P. Sequence of Events during Peptide Unbinding from RNase S: A Complete Experimental Description. J Phys Chem Lett 2021; 12:5201-5207. [PMID: 34038133 DOI: 10.1021/acs.jpclett.1c01155] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The phototriggered unbinding of the intrinsically disordered S-peptide from the RNase S complex is studied with the help of transient IR spectroscopy, covering a wide range of time scales from 100 ps to 10 ms. To that end, an azobenzene moiety has been linked to the S-peptide in a way that its helicity is disrupted by light, thereby initiating its complete unbinding. The full sequence of events is observed, starting from unfolding of the helical structure of the S-peptide on a 20 ns time scale while still being in the binding pocket of the S-protein, S-peptide unbinding after 300 μs, and the structural response of the S-protein after 3 ms. With regard to the S-peptide dynamics, the binding mechanism can be classified as an induced fit, while the structural response of the S-protein is better described as conformational selection.
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Affiliation(s)
- Brankica Jankovic
- Department of Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
| | - Jeannette Ruf
- Department of Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
| | - Claudio Zanobini
- Department of Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
| | - Olga Bozovic
- Department of Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
| | - David Buhrke
- Department of Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
| | - Peter Hamm
- Department of Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich, Switzerland
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3
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Jankovic B, Bozovic O, Hamm P. Intrinsic Dynamics of Protein-Peptide Unbinding. Biochemistry 2021; 60:1755-1763. [PMID: 33999611 DOI: 10.1021/acs.biochem.1c00262] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The dynamics of peptide-protein binding and unbinding of a variant of the RNase S system has been investigated. To initiate the process, a photoswitchable azobenzene moiety has been covalently linked to the S-peptide, thereby switching its binding affinity to the S-protein. Transient fluorescence quenching was measured with the help of a time-resolved fluorometer, which has been specifically designed for these experiments and is based on inexpensive light-emitting diodes and laser diodes only. One mutant shows on-off behavior with no specific binding detectable in one of the states of the photoswitch. Unbinding is faster by at least 2 orders of magnitude, compared to that of other variants of the RNase S system. We conclude that unbinding is essentially barrier-less in that case, revealing the intrinsic dynamics of the unbinding event, which occurs on a time scale of a few hundred microseconds in a strongly stretched-exponential manner.
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Affiliation(s)
- Brankica Jankovic
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
| | - Olga Bozovic
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
| | - Peter Hamm
- Department of Chemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
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4
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Loper J, Zhou G, Geman S. Capacities and efficient computation of first-passage probabilities. Phys Rev E 2020; 102:023304. [PMID: 32942394 DOI: 10.1103/physreve.102.023304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Accepted: 06/12/2020] [Indexed: 06/11/2023]
Abstract
A reversible diffusion process is initialized at position x_{0} and run until it first hits any of several targets. What is the probability that it terminates at a particular target? We propose a computationally efficient approach for estimating this probability, focused on those situations in which it takes a long time to hit any target. In these cases, direct simulation of the hitting probabilities becomes prohibitively expensive. On the other hand, if the timescales are sufficiently long, then the system will essentially "forget" its initial condition before it encounters a target. In these cases the hitting probabilities can be accurately approximated using only local simulations around each target, obviating the need for direct simulations. In empirical tests, we find that these local estimates can be computed in the same time it would take to compute a single direct simulation, but that they achieve an accuracy that would require thousands of direct simulation runs.
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Affiliation(s)
- Jackson Loper
- Data Science Institute, Columbia University, 10027 New York, New York, USA
| | - Guangyao Zhou
- Division of Applied Mathematics, Brown University, Providence, 02912 Rhode Island, USA
| | - Stuart Geman
- Division of Applied Mathematics, Brown University, Providence, 02912 Rhode Island, USA
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5
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Perumalla DS, Govind G, Anjukandi P. Folding‐Unfolding Dynamics of pH‐Assisted Structures of S‐Peptide. ChemistrySelect 2020. [DOI: 10.1002/slct.202000360] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
| | - Gokul Govind
- Department of Chemistry Central University of Tamil Nadu Tiruvarur India
| | - Padmesh Anjukandi
- Department of Chemistry Indian Institute of Technology Palakkad India
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6
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Vurgun N, Nitz M. Validation of l-Tellurienylalanine as a Phenylalanine Isostere. Chembiochem 2019; 21:1136-1139. [PMID: 31742805 DOI: 10.1002/cbic.201900635] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Indexed: 01/21/2023]
Abstract
Mass cytometry (MC) and imaging mass cytometry (IMCTM ) have emerged as important tools for the study of biological heterogeneity. We recently demonstrated the use of l-2-tellurienylalanine (TePhe), a mimic of phenylalanine (Phe), as an MC- and IMC-compatible protein synthesis reporter. In this work, the biochemical similarity of TePhe and its cognate analogue, Phe, are examined in the context of the RNase S complex. Isothermal titration calorimetry studies show that incorporation of TePhe preserves the interaction of S-peptide with S-protein, and the dissociation constants for the interaction of the Phe and TePhe peptides are within a factor of two. The resulting RNase S complex is catalytically active without significant alterations in the enzyme's kinetic parameters. Furthermore, circular dichroism spectroscopy does not reveal any changes to the secondary structure of TePhe-substituted RNase S. These findings provide strong evidence that TePhe functions as a Phe isostere in the context of a folded protein. It is anticipated that incorporation of TePhe into peptides or peptidomimetic scaffolds will enable facile generation of MC and IMCTM probes.
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Affiliation(s)
- Nesrin Vurgun
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, M5S 3H6, Canada
| | - Mark Nitz
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, M5S 3H6, Canada
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7
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Jankovic B, Gulzar A, Zanobini C, Bozovic O, Wolf S, Stock G, Hamm P. Photocontrolling Protein–Peptide Interactions: From Minimal Perturbation to Complete Unbinding. J Am Chem Soc 2019; 141:10702-10710. [DOI: 10.1021/jacs.9b03222] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Brankica Jankovic
- Department of Chemistry, University of Zurich, Zurich CH-8057, Switzerland
| | - Adnan Gulzar
- Biomolecular Dynamics, Institute of Physics, Albert Ludwigs University, Freiburg 79104, Germany
| | - Claudio Zanobini
- Department of Chemistry, University of Zurich, Zurich CH-8057, Switzerland
| | - Olga Bozovic
- Department of Chemistry, University of Zurich, Zurich CH-8057, Switzerland
| | - Steffen Wolf
- Biomolecular Dynamics, Institute of Physics, Albert Ludwigs University, Freiburg 79104, Germany
| | - Gerhard Stock
- Biomolecular Dynamics, Institute of Physics, Albert Ludwigs University, Freiburg 79104, Germany
| | - Peter Hamm
- Department of Chemistry, University of Zurich, Zurich CH-8057, Switzerland
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8
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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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9
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Comparative Molecular Dynamics Analysis of RNase-S Complex Formation. Biophys J 2017; 113:1466-1474. [PMID: 28978440 DOI: 10.1016/j.bpj.2017.08.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Revised: 07/25/2017] [Accepted: 08/07/2017] [Indexed: 11/20/2022] Open
Abstract
Limited proteolysis of RNase-A yields a short N-terminal S-peptide segment and the larger S-protein. Binding of S-peptide to S-protein results in the formation of an enzymatically active RNase-S protein. S-peptide undergoes a transition from intrinsic disorder to an ordered helical state upon association with S-protein to form RNase-S and is an excellent model system to study coupled folding and binding. To better understand the dynamics of the RNases-S complex and its isolated partners, comparative molecular dynamics simulations have been performed. In agreement with experiment, we find significant conformational fluctuations of the isolated S-peptide compatible with a disordered regime and only little residual helical structure. In the RNase-S complex, the N-terminal helix of S-peptide unfolds and refolds repeatedly on the microsecond timescale, indicating that the α-helical structure is only part of the equilibrium regime for these residues whereas the C-terminal residues are confined to the helical conformation that is found in the x-ray structure. This is also in line with systematic, in silico Alanine scanning free-energy simulations, which indicate that the major contribution to complex stability emerges from the C-terminal helical turn, consisting of residues 8-13 in S-peptide whereas the N-terminal S-peptide residues 1-7 make only minor contributions. Comparative simulations of S-protein in the presence and absence of S-peptide reveal that the isolated S-protein is significantly more flexible than in the complex, and undergoes a global pincerlike conformational change that narrows the S-peptide binding cleft. The narrowed binding cleft adds a barrier for complex formation likely influencing the binding kinetics. This conformational change is reversed by S-peptide association, which also stabilizes conformational fluctuations in S-protein. Such global motions associated with binding are also likely to play a role for other coupled peptide folding and binding processes at peptide binding regions on protein surfaces.
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10
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Abstract
The expression and screening of the solubility of recombinant proteins is an important step in the high-throughput (HT) production of target proteins. For many applications, E. coli remains the most widely used expression system due to the relative ease of adapting it to HT pipelines. Herein is described a platform using a 96-well format for efficient expression and solubility screening of target proteins.
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Affiliation(s)
- Keehwan Kwon
- J. Craig Venter Institute, 9704 Medical Center Drive, Rockville, MD, 20850, USA,
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11
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Rogers J, Wong CT, Clarke J. Coupled folding and binding of the disordered protein PUMA does not require particular residual structure. J Am Chem Soc 2014; 136:5197-200. [PMID: 24654952 PMCID: PMC4017604 DOI: 10.1021/ja4125065] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2013] [Indexed: 11/29/2022]
Abstract
Many cellular proteins are 'disordered' in isolation. A subset of these intrinsically disordered proteins (IDPs) can, upon binding another molecule, fold to a well-defined three-dimensional structure. In the structurally heterogeneous, unbound ensemble of these IDPs, conformations are likely to exist that, in part, resemble the final bound form. It has been suggested that these conformations, displaying 'residual structure', could be important for the mechanism of such coupled folding and binding reactions. PUMA, of the BCL-2 family, is an IDP in isolation but will form a single, contiguous α-helix upon binding the folded protein MCL-1. Using the helix-breaking residue proline, we systematically target each potential turn of helix of unbound PUMA and assess the binding to MCL-1 using time-resolved stopped-flow techniques. All proline-containing mutants bound, and although binding was weaker than the wild-type protein, association rate constants were largely unaffected. We conclude that population of particular residual structure, containing a specific helical turn, is neither required for the binding nor for fast association of PUMA and MCL-1.
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Affiliation(s)
- Joseph
M. Rogers
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, United Kingdom
| | - Chi T. Wong
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, United Kingdom
| | - Jane Clarke
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, United Kingdom
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12
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Bagchi S, Boxer SG, Fayer MD. Ribonuclease S dynamics measured using a nitrile label with 2D IR vibrational echo spectroscopy. J Phys Chem B 2012; 116:4034-42. [PMID: 22417088 PMCID: PMC3354990 DOI: 10.1021/jp2122856] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
A nitrile-labeled amino acid, p-cyanophenylalanine, is introduced near the active site of the semisynthetic enzyme ribonuclease S to serve as a probe of protein dynamics and fluctuations. Ribonuclease S is the limited proteolysis product of subtilisin acting on ribonuclease A, and consists of a small fragment including amino acids 1-20, the S-peptide, and a larger fragment including residues 21-124, the S-protein. A series of two-dimensional vibrational echo experiments performed on the nitrile-labeled S-peptide and the RNase S are described. The time-dependent changes in the two-dimensional infrared vibrational echo line shapes are analyzed using the center line slope method to obtain the frequency-frequency correlation function (FFCF). The observations show that the nitrile probe in the S-peptide has dynamics that are similar to, but faster than, those of the single amino acid p-cyanophenylalanine in water. In contrast, the dynamics of the nitrile label when the peptide is bound to form ribonuclease S are dominated by homogeneous dephasing (motionally narrowed) contributions with only a small contribution from very fast inhomogeneous structural dynamics. The results provide insights into the nature of the structural dynamics of the ribonuclease S complex. The equilibrium dynamics of the nitrile labeled S-peptide and the ribonuclease S complex are also investigated by molecular dynamics simulations. The experimentally determined FFCFs are compared to the FFCFs obtained from the molecular dynamics simulations, thereby testing the capacity of simulations to determine the amplitudes and time scales of protein structural fluctuations on fast time scales under thermal equilibrium conditions.
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Affiliation(s)
- Sayan Bagchi
- Department of Chemistry, Stanford University, Stanford, California 94305
| | - Steven G. Boxer
- Department of Chemistry, Stanford University, Stanford, California 94305
| | - M. D. Fayer
- Department of Chemistry, Stanford University, Stanford, California 94305
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13
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Chène P. Can biochemistry drive drug discovery beyond simple potency measurements? Drug Discov Today 2012; 17:388-95. [DOI: 10.1016/j.drudis.2012.01.022] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2011] [Revised: 01/23/2012] [Accepted: 01/25/2012] [Indexed: 10/14/2022]
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14
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Karlsson OA, Chi CN, Engström A, Jemth P. The transition state of coupled folding and binding for a flexible β-finger. J Mol Biol 2012; 417:253-61. [PMID: 22310047 DOI: 10.1016/j.jmb.2012.01.042] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Revised: 01/13/2012] [Accepted: 01/25/2012] [Indexed: 12/19/2022]
Abstract
Flexible and fully disordered protein regions that fold upon binding mediate numerous protein-protein interactions. However, little is known about their mechanism of interaction. One such coupled folding and binding occurs when a flexible region of neuronal nitric oxide synthase adopts a β-finger structure upon binding to its protein ligand, a PDZ [PSD-95 (postsynaptic density protein-95)/Discs large/ZO-1] domain from PSD-95. We have analyzed this binding reaction by protein engineering combined with kinetic experiments. Mutational destabilization of the β-finger changed mainly the dissociation rate constant of the proteins and, to a lesser extent, the association rate constant. Thus, mutation affected late events in the coupled folding and binding reaction. Our results therefore suggest that the native binding interactions of the β-finger are not present in the rate-limiting transition state for binding but form on the downhill side in a cooperative manner. However, by mutation, we could destabilize the β-finger further and change the rate-limiting step such that an initial conformational change becomes rate limiting. This switch in rate-limiting step shows that multistep binding mechanisms are likely to be found among flexible and intrinsically disordered regions of proteins.
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Affiliation(s)
- O Andreas Karlsson
- Department of Medical Biochemistry and Microbiology, Uppsala University, SE-75123 Uppsala, Sweden
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15
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Kiefhaber T, Bachmann A, Jensen KS. Dynamics and mechanisms of coupled protein folding and binding reactions. Curr Opin Struct Biol 2011; 22:21-9. [PMID: 22129832 DOI: 10.1016/j.sbi.2011.09.010] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Accepted: 09/27/2011] [Indexed: 11/28/2022]
Abstract
Protein folding coupled to binding of a specific ligand is frequently observed in biological processes. In recent years numerous studies have addressed the structural properties of the unfolded proteins in the absence of their ligands. Surprisingly few time-resolved investigations on coupled folding and binding reactions have been published up to date and the dynamics and kinetic mechanisms of these processes are still only poorly understood. Especially, it is still unsolved for most systems which conformation of the protein is recognized by the ligand (conformational selection vs. folding-after-binding) and whether the ligand influences the folding kinetics. Here we review experimental methods, kinetic models and time-resolved experimental studies of coupled folding and binding reactions.
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Affiliation(s)
- Thomas Kiefhaber
- Munich Center for Integrated Protein Science at the Chemistry Department, TU München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
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16
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Prakash MK. Insights on the Role of (Dis)order from Protein–Protein Interaction Linear Free-Energy Relationships. J Am Chem Soc 2011; 133:9976-9. [DOI: 10.1021/ja201500z] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Meher K. Prakash
- Chemistry and Applied Biosciences Division, ETH Zürich, USI Campus, CH 6900 Lugano, Switzerland
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17
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Mapping backbone and side-chain interactions in the transition state of a coupled protein folding and binding reaction. Proc Natl Acad Sci U S A 2011; 108:3952-7. [PMID: 21325613 DOI: 10.1073/pnas.1012668108] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Understanding the mechanism of protein folding requires a detailed knowledge of the structural properties of the barriers separating unfolded from native conformations. The S-peptide from ribonuclease S forms its α-helical structure only upon binding to the folded S-protein. We characterized the transition state for this binding-induced folding reaction at high resolution by determining the effect of site-specific backbone thioxylation and side-chain modifications on the kinetics and thermodynamics of the reaction, which allows us to monitor formation of backbone hydrogen bonds and side-chain interactions in the transition state. The experiments reveal that α-helical structure in the S-peptide is absent in the transition state of binding. Recognition between the unfolded S-peptide and the S-protein is mediated by loosely packed hydrophobic side-chain interactions in two well defined regions on the S-peptide. Close packing and helix formation occurs rapidly after binding. Introducing hydrophobic residues at positions outside the recognition region can drastically slow down association.
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18
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Abstract
Three different nitrile-containing amino acids, p-cyanophenylalanine, m-cyanophenylalanine, and S-cyanohomocysteine, have been introduced near the active site of the semisynthetic enzyme ribonuclease S (RNase S) to serve as probes of electrostatic fields. Vibrational Stark spectra, measured directly on the probe-modified proteins, confirm the predominance of the linear Stark tuning rate in describing the sensitivity of the nitrile stretch to external electric fields, a necessary property for interpreting observed frequency shifts as a quantitative measure of local electric fields that can be compared with simulations. The X-ray structures of these nitrile-modified RNase variants and enzymatic assays demonstrate minimal perturbation to the structure and function, respectively, by the probes and provide a context for understanding the influence of the environment on the nitrile stretching frequency. We examine the ability of simulation techniques to recapitulate the spectroscopic properties of these nitriles as a means to directly test a computational electrostatic model for proteins, specifically that in the ubiquitous Amber-99 force field. Although qualitative agreement between theory and experiment is observed for the largest shifts, substantial discrepancies are observed in some cases, highlighting the ongoing need for experimental metrics to inform the development of theoretical models of electrostatic fields in proteins.
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Affiliation(s)
- Aaron Fafarman
- Department of Chemistry Stanford University Stanford, California 94305-5080
| | - Steven G. Boxer
- Department of Chemistry Stanford University Stanford, California 94305-5080
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19
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Vilà R, Benito A, Ribó M, Vilanova M. Mapping the stability clusters in bovine pancreatic ribonuclease A. Biopolymers 2010; 91:1038-47. [PMID: 19373927 DOI: 10.1002/bip.21204] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In the present work, we have thermodynamically characterized the thermally induced unfolding of 20 variants of bovine pancreatic ribonuclease A (RNase A) to experimentally describe the residues and the regions that are critical for the stability of the enzyme. The achieved results, complemented with previous studies by our group, allowed us to define the significance of the two hydrophobic nuclei present in the RNase A structure, as well as the contribution of the participating residues within each nucleus, to the global enzyme stability. We propose a structural model for the major and the minor hydrophobic nuclei of RNase A. The major nucleus is composite and located in the cavity delimited by alpha-helices 1 and 3, and the beta-sheet that is formed by strands 2, 3, 5, and 6. It consists of a central tight packed part constituted by residues Phe8, Met13, Val54, Val57, Ile106, Val108, and Phe120. This central part is surrounded by a layer formed by residues Val63, Tyr73, Met79, Ile107, Val116, and Val118. The minor nucleus, although less complex, is also constituted by a tight packing that involves the side chains of residues Tyr25, Met29, Met30, Leu35, Phe46, and Tyr97, which fill the cavity that originates the beta-sheet formed by beta-strands 1, 4, and 5 together with alpha-helix2.
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Affiliation(s)
- Roger Vilà
- Departament de Biologia, Universitat de Girona, Campus de Montilivi s/n 17071 Girona, Spain
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20
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Rai J. Interaction energy analysis of peptide can predict the possibilities of mimetics by its retroinverso isomer. Chem Biol Drug Des 2009; 74:483-7. [PMID: 19811507 DOI: 10.1111/j.1747-0285.2009.00868.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
It has been previously reported that the retroinverso analog of S peptide cannot mimic the S peptide, whereas the retroinverso analog of foot-and-mouth disease virus antigen can mimic the foot-and-mouth disease virus antigen. The structures of S peptide, foot-and-mouth disease virus antigen, and their retroinverso analogs are known. Here, we have attempted to explain the structural basis of mimetics at the level of atomic interactions by elaborating upon the Guptasarma's hypothesis. Using interaction energy analysis of S peptide and foot-and-mouth disease virus antigen, we propose that if the energy of the CO and NH backbone atoms' non-covalent interactions with all other atoms is negligible as compared with the energy of other non-covalent interactions, then the retroinverso isomer can mimic the original peptide/protein. Previous work has established that the structure of the inverso analog of a protein will be the mirror image of the protein, and it will only recognize the respective mirror image substrate/binding partner. The retro peptide conformation that can be superimposed on all side chains in any conformation of the original peptide does not exist in the conformational space of the peptides.
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Affiliation(s)
- Jagdish Rai
- International Centre For Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi, India.
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21
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Rumfeldt JAO, Galvagnion C, Vassall KA, Meiering EM. Conformational stability and folding mechanisms of dimeric proteins. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 98:61-84. [PMID: 18602415 DOI: 10.1016/j.pbiomolbio.2008.05.004] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The folding of multisubunit proteins is of tremendous biological significance since the large majority of proteins exist as protein-protein complexes. Extensive experimental and computational studies have provided fundamental insights into the principles of folding of small monomeric proteins. Recently, important advances have been made in extending folding studies to multisubunit proteins, in particular homodimeric proteins. This review summarizes the equilibrium and kinetic theory and models underlying the quantitative analysis of dimeric protein folding using chemical denaturation, as well as the experimental results that have been obtained. Although various principles identified for monomer folding also apply to the folding of dimeric proteins, the effects of subunit association can manifest in complex ways, and are frequently overlooked. Changes in molecularity typically give rise to very different overall folding behaviour than is observed for monomeric proteins. The results obtained for dimers have provided key insights pertinent to understanding biological assembly and regulation of multisubunit proteins. These advances have set the stage for future advances in folding involving protein-protein interactions for natural multisubunit proteins and unnatural assemblies involved in disease.
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Affiliation(s)
- Jessica A O Rumfeldt
- Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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22
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Abstract
The S peptide from ribonuclease S was used as a model system to explore the relationship between the native peptide and its retroinverso (RI) analog. As probed by circular dichroism, the conformations of S peptide and retroinverso S peptide (RIS peptide) are each right-handed helical conformation. The helical propensity of retro S peptide is greater than S peptide, in trifluoroethanol (TFE). In 70% TFE, the S peptide possesses greater helicity at pH 4 than at pH 7, whereas RIS peptide possesses greater helicity at pH 7 than at pH 4. The RIS peptide does not mimic the S peptide in binding to S protein. Specifically, the RIS peptide does not mimic the S peptide to effect RNase activity with S protein and it also does not inhibit the RNase activity of S peptide with S protein. The biological mimicry between the S peptide and its RIS analog depends on the conformation and relatedness of both the side chain and backbone substructures. The backbones in the S peptide and its RIS analog are reverted with respect to each other; however, the side chain patterns are predicted to be similar. Importantly, if the molecular interactions of backbone atoms of the S peptide and its binding to S protein, then the RIS analog would be unlikely to mimic this parent peptide.
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23
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Kwon K, Pieper R, Shallom S, Grose C, Kwon E, Do Y, Latham S, Alami H, Huang ST, Gatlin C, Papazisi L, Fleischmann R, Peterson S. A correlation analysis of protein characteristics associated with genome-wide high throughput expression and solubility of Streptococcus pneumoniae proteins. Protein Expr Purif 2007; 55:368-78. [PMID: 17703947 DOI: 10.1016/j.pep.2007.06.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2007] [Revised: 06/12/2007] [Accepted: 06/18/2007] [Indexed: 12/01/2022]
Abstract
We have developed and evaluated a highly parallel protein expression and purification system using ORFs derived from the pathogenic bacterium Streptococcus pneumoniae as a representative test case in conjunction with the Gateway cloning technology. Establishing high throughput protein production capability is essential for genome-wide characterization of protein function. In this study, we focused on protein expression and purification outcomes generated from an expression vector which encodes an NH(2)-terminal hexa-histidine tag and a COOH-terminal S-tag. Purified recombinant proteins were validated by SDS-PAGE, followed by in-gel digestion and identification by MALDI-TOF/TOF analysis. Starting with 1360 sequence-validated destination clones we examined correlation analyses of expression and solubility of a wide variety of recombinant proteins. In total, 428 purified proteins (31%) were recovered in soluble form. We describe a semi-quantitative scoring method using an S-tag assay to improve the throughput and efficiency of expression and solubility studies for recombinant proteins. Given a relatively large dataset derived from proteins representing all functional groups in a microbial genome we correlated various protein characteristics as they relate to protein expression outcomes.
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Affiliation(s)
- Keehwan Kwon
- J. Craig Venter Institute, 9704 Medical Center Drive, Rockville, MD 20850, USA
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24
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Long F, McElheny D, Jiang S, Park S, Caffrey MS, Fung LWM. Conformational change of erythroid alpha-spectrin at the tetramerization site upon binding beta-spectrin. Protein Sci 2007; 16:2519-30. [PMID: 17905835 PMCID: PMC2211704 DOI: 10.1110/ps.073115307] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
We previously determined the solution structures of the first 156 residues of human erythroid alpha-spectrin (SpalphaI-1-156, or simply Spalpha). Spalpha consists of the tetramerization site of alpha-spectrin and associates with a model beta-spectrin protein (Spbeta) with an affinity similar to that of native alpha- and beta-spectrin. Upon alphabeta-complex formation, our previous results indicate that there is an increase in helicity in the complex, suggesting conformational change in either Spalpha or Spbeta or in both. We have now used isothermal titration calorimetry, circular dichroism, static and dynamic light scattering, and solution NMR methods to investigate properties of the complex as well as the conformation of Spalpha in the complex. The results reveal a highly asymmetric complex, with a Perrin shape parameter of 1.23, which could correspond to a prolate ellipsoid with a major axis of about five and a minor axis of about one. We identified 12 residues, five prior to and seven following the partial domain helix in Spalpha that moved freely relative to the structural domain in the absence of Spbeta but when in the complex moved with a mobility similar to that of the structural domain. Thus, it appears that the association with Spbeta induced an unstructured-to-helical conformational transition in these residues to produce a rigid and asymmetric complex. Our findings may provide insight toward understanding different association affinities of alphabeta-spectrin at the tetramerization site for erythroid and non-erythroid spectrin and a possible mechanism to understand some of the clinical mutations, such as L49F of alpha-spectrin, which occur outside the functional partial domain region.
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Affiliation(s)
- Fei Long
- Department of Chemistry, University of Illinois at Chicago 60607, USA
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25
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Fafarman AT, Webb LJ, Chuang JI, Boxer SG. Site-specific conversion of cysteine thiols into thiocyanate creates an IR probe for electric fields in proteins. J Am Chem Soc 2007; 128:13356-7. [PMID: 17031938 PMCID: PMC2516909 DOI: 10.1021/ja0650403] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The nitrile stretching mode of the thiocyanate moiety is a nearly ideal probe for measuring the local electric field arising from the organized environment of the interior of a protein. Nitriles were introduced into three proteins: ribonuclease S (RNase S), human aldose reductase (hALR2), and the reaction center (RC) of Rhodobacter capsulatus, through a facile synthetic scheme for the transformation of cysteine residues into thiocyanatoalanine. Vibrational Stark effect spectroscopy and Fourier transform infrared spectroscopy on the modified proteins demonstrated that thiocyanate residues are a highly general tool for probing electrostatic fields in proteins.
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Affiliation(s)
- Aaron T Fafarman
- Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA
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26
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Abstract
The phenolic pKa of fluorescein varies depending on its environment. The fluorescence of the dye varies likewise. Accordingly, a change in fluorescence can report on the association of a fluorescein conjugate to another molecule. Here, we demonstrate how to optimize this process with chemical synthesis. The fluorescence of fluorescein-labeled model protein, bovine pancreatic ribonuclease (RNase A), decreases upon binding to its cognate inhibitor protein (RI). Free and RI-bound fluorescein-RNase A have pKa values of 6.35 and 6.70, respectively, leaving the fluorescein moiety largely unprotonated at physiological pH and thus limiting the sensitivity of the assay. To increase the fluorescein pKa and, hence, the assay sensitivity, we installed an electron-donating alkyl group ortho to each phenol group. 2',7'-Diethylfluorescein (DEF) has spectral properties similar to those of fluorescein but a higher phenolic pKa. Most importantly, free and RI-bound DEF-RNase A have pKa values of 6.68 and 7.29, respectively, resulting in a substantial increase in the sensitivity of the assay. Using DEF-RNase A rather than fluorescein-RNase A in a microplate assay at pH 7.12 increased the Z'-factor from -0.17 to 0.69. We propose that synthetic "tuning" of the pKa of fluorescein and other pH-sensitive fluorophores provides a general means to optimize binding assays.
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Affiliation(s)
| | | | - Ronald T. Raines
- Corresponding author. Department of Biochemistry, University of Wisconsin–Madison, 433 Babcock Drive, Madison, Wisconsin 53706-1544; Phone: 608-262-8588. Fax: 608-262-3453.
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27
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Mahmoud KA, Kraatz HB. A Bioorganometallic Approach for the Electrochemical Detection of Proteins: A Study on the Interaction of Ferrocene–Peptide Conjugates with Papain in Solution and on Au Surfaces. Chemistry 2007; 13:5885-95. [PMID: 17455185 DOI: 10.1002/chem.200601878] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
In this paper, a new bioorganometallic approach for the detection of proteins using surface-bound ferrocene-peptide conjugates is presented. Specifically, a series of peptide conjugates of 1'-aminoferrocene-1-carboxylic acid (ferrocene amino acid, Fca) is synthesized: Boc-Fca-Gly-Gly-Tyr(Bzl)-Arg(NO2)-OMe (2), Thc-Fca-Gly-Gly-Tyr(Bzl)-Arg(NO2)-OMe (3), Thc-Fca-Gly-Gly-Tyr(Bzl)-Arg(NO2)-OH (4), Boc-Fca-Gly-Gly-Arg(Mtr)-Tyr-OMe (7), Thc-Fca-Gly-Gly-Arg(Mtr)-Tyr-OMe (8), Thc-Fca-Gly-Gly-Arg(Mtr)-Tyr-OH (9), Thc-Fca-Gly-Gly-Arg-Tyr-OH (10). The peptide is conjugated to the C-terminal side of Fca and compounds 4, 7-10 possess a thiostic acid linked to the N-terminal side of Fca in order to facilitate formation of thin films on gold substrates. Competitive inhibition towards papain was determined for Thc-Fca-Gly-Gly-Tyr(Bzl)-Arg(NO2)-OH (4), Thc-Fca-Gly-Gly-Arg(Mtr)-Tyr-OH (9) and Thc-Fca-Gly-Gly-Arg-Tyr-OH (10). The binding interaction between the peptide modified substrates and papain enzyme was studied using real-time surface plasmon resonance (SPR) imaging. Peptide 10 showed the strongest binding affinity to papain. Adsorption/desorption rate constants were ka = 1.75+/-0.05 x 10(5) M(-1) s(-1) and kd = 2.90 +/- 0.05 x 10(-2) s(-1). Interactions of papain with Fca-peptide 10 were investigated by cyclic voltammetry. The interaction results were also verified by measuring the electrochemical response of the peptide-papain interaction as function of increasing enzyme concentration. A linear relationship was observed for papain concentration of up to 80 nM. Shifting to higher potentials as well as decrease in the overall signal intensity was observed. The detection limit was 4 x 10(-9) M.
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Affiliation(s)
- Khaled A Mahmoud
- Department of Chemistry, University Of Saskatchewan, Saskatoon, SK S7N 5C9, Canada
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28
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Font J, Benito A, Torrent J, Lange R, Ribó M, Vilanova M. Pressure- and temperature-induced unfolding studies: thermodynamics of core hydrophobicity and packing of ribonuclease A. Biol Chem 2006; 387:285-96. [PMID: 16542150 DOI: 10.1515/bc.2006.038] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractIn this work we demonstrate that heat and pressure induce only slightly different energetic changes in the unfolded state of RNase A. Using pressure and temperature as denaturants on a significant number of variants, and by determining the free energy of unfolding at different temperatures, we estimated the stability of variants unable to complete the unfolding transition owing to the experimental conditions required for pressure experiments. The overall set of results allowed us to map the contributions to stability of the hydrophobic core residues of RNase A, with the positions most critical for stability being V54, V57, I106 and V108. We also show that the stability differences can be attributed to both hydrophobic interactions and packing density with an equivalent energetic magnitude. The main hydrophobic core of RNase A is tightly packed, as shown by the small-to-large and isosteric substitutions. In addition, we found that large changes in the number of methylene groups have non-additive positive stability interaction energies that are consistent with exquisite tight core packing and rearrangements of van der Waals' interactions in the protein interior, even after drastic deleterious substitutions.
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Affiliation(s)
- Josep Font
- Laboratori d'Enginyeria de Proteïnes, Departament de Biologia, Facultat de Ciències, Universitat de Girona, Campus de Montilivi s/n, E-17071 Girona, Spain
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29
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McLeish TCB. Diffusive searches in high-dimensional spaces and apparent 'two-state' behaviour in protein folding. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2006; 18:1861-1868. [PMID: 21697560 DOI: 10.1088/0953-8984/18/6/003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We extend a simple model for protein folding as a high-dimensional diffusive search. By solving a steady-state diffusion equation on a hypersphere centred on an absorbing 'native state' we find the general property that the kinetics of such a search will always be nearly single exponential. This explains the common observation of such simple 'two-state' folding kinetics in models that contain considerable intermediate structure. It also suggests that the experimental signature of single-exponential folding kinetics does not imply a simple two-state structure to the folding space.
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Affiliation(s)
- T C B McLeish
- Department of Physics and Astronomy and Astbury Centre for Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
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30
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Lee HJ, Yan Y, Marriott G, Corn RM. Quantitative functional analysis of protein complexes on surfaces. J Physiol 2004; 563:61-71. [PMID: 15613368 PMCID: PMC1665573 DOI: 10.1113/jphysiol.2004.081117] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
A major challenge in cell and molecular physiology research is to understand the mechanisms of biological processes in terms of the interactions, activities and regulation of the underlying proteins. Functional and mechanistic analyses of the large number of proteins that participate in the regulation of cellular processes will require new approaches and techniques for high throughput and multiplexed functional analyses of protein interactions, protein conformational dynamics and protein activity. In this review we focus on the development and application of proteomics and associated technologies for quantitative functional analysis of proteins and their complexes that include: (1) the application of surface plasmon resonance (SPR) imaging for multiplexed, label-free analyses of protein interactions, binding constants for biomolecular interactions and protein activities; and (2) high content analysis of protein motions within functional multiprotein complexes.
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Affiliation(s)
- Hye Jin Lee
- Department of Physiology, University of Wisconsin-Madison, WI 53706, USA
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31
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McLeish TCB. Protein folding in high-dimensional spaces: hypergutters and the role of nonnative interactions. Biophys J 2004; 88:172-83. [PMID: 15501939 PMCID: PMC1304996 DOI: 10.1529/biophysj.103.036616] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We explore the consequences of very high dimensionality in the dynamical landscape of protein folding. Consideration of both typical range of stabilizing interactions, and folding rates themselves, leads to a model of the energy hypersurface that is characterized by the structure of diffusive "hypergutters" as well as the familiar "funnels". Several general predictions result: 1), intermediate subspaces of configurations will always be visited; 2), specific but nonnative interactions may be important in stabilizing these low-dimensional diffusive searches on the folding pathway, as well as native interactions; 3), sequential barriers will commonly be found, even in "two-state" proteins; 4), very early times will show characteristic departures from single-exponential kinetics; and 5), contributions of nonnative interactions to Phi-values and "Chevron plots" are calculable, and may be significant. The example of a three-helix bundle is treated in more detail as an illustration. The model also shows that high-dimensional structures provide conceptual relations between different models of protein folding. It suggests that kinetic strategies for fast folding may be encoded rather generally in nonnative as well as in native interactions. The predictions are related to very recent findings in experiment and simulation.
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Affiliation(s)
- T C B McLeish
- Department of Physics and Astronomy and Astbury Centre for Molecular Biology, University of Leeds, Leeds, United Kingdom.
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32
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Backer MV, Gaynutdinov TI, Gorshkova II, Crouch RJ, Hu T, Aloise R, Arab M, Przekop K, Backer JM. Humanized docking system for assembly of targeting drug delivery complexes. J Control Release 2003; 89:499-511. [PMID: 12737851 DOI: 10.1016/s0168-3659(03)00150-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Targeted drug delivery requires 'loading' drugs onto targeting proteins. Traditional technologies for loading drugs rely on chemical conjugation of drugs or drug carriers to targeting proteins. An alternative approach might rely on assembly of targeting complexes using a docking system that includes two components: a 'docking' tag fused to a targeting protein, and a 'payload' module containing an adapter protein for non-covalent binding to the docking tag. We describe here a fully humanized adapter/docking tag system based on non-covalent interaction between two fragments of human pancreatic RNase I. A 15 amino acid long N-terminal fragment of RNase I designed to serve as a docking tag, was fused to the N-terminus of human vascular endothelial growth factor that served as a targeting protein. An 18-125 and an 18-127 amino acid long fragments of RNase I were engineered, expressed and refolded into active conformations to serve as adapter proteins. Interactions between the targeting and adapter proteins were characterized using enzymatic analysis and surface plasmon resonance. Targeting DNA delivery complexes were assembled, characterized by dynamic light scattering, and found to be very effective in receptor-mediated DNA delivery.
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Affiliation(s)
- Marina V Backer
- SibTech, Inc, 705 North Mountain Road, Newington, CT 06111, USA.
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33
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Bartley LE, Zhuang X, Das R, Chu S, Herschlag D. Exploration of the transition state for tertiary structure formation between an RNA helix and a large structured RNA. J Mol Biol 2003; 328:1011-26. [PMID: 12729738 DOI: 10.1016/s0022-2836(03)00272-9] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Docking of the P1 duplex into the pre-folded core of the Tetrahymena group I ribozyme exemplifies the formation of tertiary interactions in the context of a complex, structured RNA. We have applied Phi-analysis to P1 docking, which compares the effects of modifications on the rate constant for docking (k(dock)) with the effects on the docking equilibrium (K(dock)). To accomplish this we used a single molecule fluorescence resonance energy transfer assay that allows direct determination of the rate constants for formation of thermodynamically favorable, as well as unfavorable, states. Modification of the eight groups of the P1 duplex that make tertiary interactions with the core and changes in solution conditions decrease K(dock) up to 500-fold, whereas k(dock) changes by </=2-fold. The absence of effects on k(dock), both from atomic modifications and global perturbations, strongly suggests that the transition state for docking is early and does not closely resemble the docked state. These results, the slow rate of docking of 3s(-1), and the observation that a modification that is expected to increase the degrees of freedom between the P1 duplex and the ribozyme core accelerates docking, suggest a model in which a kinetic trap(s) slows docking substantially. Nonetheless, urea does not increase k(dock), suggesting that there is little change in the exposed surface area between the trapped, undocked state and the transition state. The findings highlight that urea and temperature dependencies can be inadequate to diagnose the presence of kinetic traps in a folding process. The results described here, combined with previous work, provide an in-depth view of an RNA tertiary structure formation event and suggest that large, highly structured RNAs may have local regions that are misordered.
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Affiliation(s)
- Laura E Bartley
- Department of Biochemistry, B400 Beckman Center, Stanford University, Stanford, CA 94305-5307, USA
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34
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Abstract
An explosion of in vitro experimental data on the folding of proteins has revealed many examples of folding in the millisecond or faster timescale, often occurring in the absence of stable intermediate states. We review experimental methods for measuring fast protein folding kinetics, and then discuss various analytical models used to interpret these data. Finally, we classify general mechanisms that have been proposed to explain fast protein folding into two catagories, heterogeneous and homogeneous, reflecting the nature of the transition state. One heterogeneous mechanism, the diffusion-collision mechanism, can be used to interpret experimental data for a number of proteins.
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Affiliation(s)
- Jeffrey K Myers
- Department of Biochemistry, Duke University Medical Center, Box 3711, Durham, North Carolina 27710, USA.
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35
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Benito A, Bosch M, Torrent G, Ribó M, Vilanova M. Stabilization of human pancreatic ribonuclease through mutation at its N-terminal edge. Protein Eng Des Sel 2002; 15:887-93. [PMID: 12538908 DOI: 10.1093/protein/15.11.887] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Enzyme stability can be an important parameter in the design of recombinant toxins because unstable proteins are often degraded before they can reach their cellular target. There is great interest in the design of human pancreatic ribonuclease variants that could be cytotoxic against tumoral cells. To this end, some residues in the protein need to be substituted, but this may result in a loss of stability. Previous papers have reported the production of N- and C-terminal human pancreatic ribonuclease variants with increased thermal stability. Here, we investigated the contribution of the different amino acid changes at the N-terminus of the protein to its thermostability increase. We show that this increase correlates with the helical propensity of the first alpha-helix of the protein. On the other hand, deletion of the four last residues of the protein does not affect its thermal stability. These results set the basis for the design of a human pancreatic ribonuclease template on which amino acid substitutions can be made that could render the enzyme cytotoxic, without an important loss in its stability.
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Affiliation(s)
- A Benito
- Laboratori d'Enginyeria de Proteïnes, Departament de Biologia, Facultat de Ciències, Universitat de Girona, Campus Montilivi, 17071 Girona, Spain
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36
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Abel RL, Haigis MC, Park C, Raines RT. Fluorescence assay for the binding of ribonuclease A to the ribonuclease inhibitor protein. Anal Biochem 2002; 306:100-7. [PMID: 12069420 DOI: 10.1006/abio.2002.5678] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ribonuclease A (RNase A) and the ribonuclease inhibitor protein (RI) form one of the tightest known protein-protein complexes. RNase A variants and homologues, such as G88R RNase A, that retain ribonucleolytic activity in the presence of RI are toxic to cancer cells. Herein, a new and facile assay is described for measuring the equilibrium dissociation constant (K(d)) and dissociation rate constant (k(d)) for complexes of RI and RNase A. This assay is based on the decrease in fluorescence intensity that occurs when a fluorescein-labeled RNase A binds to RI. To allow time for equilibration, the assay is most readily applied to those complexes with K(d) values in the nanomolar range or higher. Using this assay, the value of K(d) for the complex of RI with fluorescein-labeled G88R RNase A was determined to be 0.55 +/- 0.03 nM. In addition, the value of K(d) was determined for the complex of RI with unlabeled G88R RNase A to be 0.57 +/- 0.05 nM by using a competition assay with fluorescein-labeled G88R RNase A. Finally, the value of k(d) for the complex of RI with fluorescein-labeled G88R RNase A was determined to be (7.5 +/- 0.4) x 10(-3) s(-1) by monitoring the increase in fluorescence intensity upon dissociation. This assay can be used to characterize complexes of RI with a wide variety of RNase A variants and homologues, including those with cytotoxic activity.
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Affiliation(s)
- Richele L Abel
- Department of Biochemistry, University of Wisconsin at Madison, Madison, Wisconsin 53706, USA
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37
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James DA, Burns DC, Woolley GA. Kinetic characterization of ribonuclease S mutants containing photoisomerizable phenylazophenylalanine residues. Protein Eng Des Sel 2001; 14:983-91. [PMID: 11809929 DOI: 10.1093/protein/14.12.983] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Incorporation of the photoisomerizable amino acid phenylazophenylalanine (PAP) into enzyme structures has been proposed as a strategy for photoswitching enzyme activity. To evaluate the strengths and limitations of this approach to enzyme photo-control, we performed a kinetic analysis of RNase S analogues containing PAP in positions 4, 7, 8, 10, 11 or 13. For an enzyme containing a single PAP group, the maximum extent of photoconversion (between approximately 96% trans/4% cis and 10% trans/90% cis under standard conditions) sets a limit on the maximum fold change in the initial rate of approximately 25-fold, if the cis form is the more active isomer, and approximately 10-fold if the trans form is more active. This extent of photoswitching was not realized in the present case because the effects of photoisomerization on kinetic constants were small and distributed among effects on S-peptide binding, substrate binding and the rate of the chemical step. These results suggest that photoisomerization could substantially alter enzyme kinetic constants but that a directed combinatorial approach might be required for realizing maximal photo-control in such systems. The limit set by the extent of photoconversion might be overcome by coupling multiple PAP groups to one enzyme or by altering the behaviour of a system that required oligomerization for activity.
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Affiliation(s)
- D A James
- Department of Chemistry, University of Toronto, 80 St George St., Toronto, Canada, M5S 3H6
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38
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Ojennus DD, Fleissner MR, Wuttke DS. Reconstitution of a native-like SH2 domain from disordered peptide fragments examined by multidimensional heteronuclear NMR. Protein Sci 2001; 10:2162-75. [PMID: 11604523 PMCID: PMC2374061 DOI: 10.1110/ps.18701] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2001] [Revised: 07/16/2001] [Accepted: 07/25/2001] [Indexed: 10/14/2022]
Abstract
The N-terminal SH2 domain from the p85alpha subunit of phosphatidylinositol 3' kinase is cleaved specifically into 9- and 5-kD fragments by limited proteolytic digestion with trypsin. The noncovalent SH2 domain complex and its constituent tryptic peptides have been investigated using high-resolution heteronuclear magnetic resonance (NMR). These studies have established the viability of the SH2 domain as a fragment complementation system. The individual peptide fragments are predominantly unstructured in solution. In contrast, the noncovalent 9-kD + 5-kD complex shows a native-like (1)H-(15)N HSQC spectrum, demonstrating that the two fragments fold into a native-like structure on binding. Chemical shift analysis of the noncovalent complex compared to the native SH2 domain reveals that the highest degree of perturbation in the structure occurs at the cleavage site within a flexible loop and along the hydrophobic interface between the two peptide fragments. Mapping of these chemical shift changes on the structure of the domain reveals changes consistent with the reduction in affinity for the target peptide ligand observed in the noncovalent complex relative to the intact protein. The 5-kD fragment of the homologous Src protein is incapable of structurally complementing the p85 9-kD fragment, either in complex formation or in the context of the full-length protein. These high-resolution structural studies of the SH2 domain fragment complementation features establish the suitability of the system for further protein-folding and design studies.
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Affiliation(s)
- D D Ojennus
- Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309-0215, USA
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Singla SI, Hudmon A, Goldberg JM, Smith JL, Schulman H. Molecular characterization of calmodulin trapping by calcium/calmodulin-dependent protein kinase II. J Biol Chem 2001; 276:29353-60. [PMID: 11384969 DOI: 10.1074/jbc.m101744200] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Autophosphorylation of alpha-Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II) at Thr(286) results in calmodulin (CaM) trapping, a >10,000-fold decrease in the dissociation rate of CaM from the enzyme. Here we present the first site-directed mutagenesis study on the dissociation of the high affinity complex between CaM and full-length CaM kinase II. We measured dissociation kinetics of CaM and CaM kinase II proteins by using a fluorescently modified CaM that is sensitive to binding to target proteins. In low [Ca(2+)], the phosphorylated mutant kinase F293A and the CaM mutant E120A/M124A exhibited deficient trapping compared with wild-type. In high [Ca(2+)], the CaM mutations E120A, M124A, and E120A/M124A and the CaM kinase II mutations F293A, F293E, N294A, N294P, and R297E increased dissociation rate constants by factors ranging from 2.3 to 116. We have also identified residues in CaM and CaM kinase II that interact in the trapped state by mutant cycle-based analysis, which suggests that interactions between Phe(293) in the kinase and Glu(120) and Met(124) in CaM specifically stabilize the trapped CaM-CaM kinase II complex. Our studies further show that Phe(293) and Asn(294) in CaM kinase II play dual roles, because they likely destabilize the low affinity state of CaM complexed to unphosphorylated kinase but stabilize the trapped state of CaM bound to phosphorylated kinase.
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Affiliation(s)
- S I Singla
- Department of Neurobiology, Stanford University School of Medicine, Stanford, California 94305-5125, USA
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Abstract
This review focuses on a very important but little understood type of molecular recognition--the recognition between highly flexible molecular structures. The formation of a specific complex in this case is a dynamic process that can occur through sequential steps of mutual conformational adaptation. This allows modulation of specificity and affinity of interaction in extremely broad ranges. The interacting partners can interact together to form a complex with entirely new properties and produce conformational signal transduction at substantial distance. We show that this type of recognition is frequent in formation of different protein-protein and protein-nucleic acid complexes. It is also characteristic for self-assembly of protein molecules from their unfolded fragments as well as for interaction of molecular chaperones with their substrates and it can be the origin of 'protein misfolding' diseases. Thermodynamic and kinetic features of this type of dynamic recognition and the principles underlying their modeling and analysis are discussed.
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Affiliation(s)
- A P Demchenko
- The Palladin Institute of Biochemistry of the Academy of Sciences of Ukraine, Kiev 252030, Ukraine.
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Stacey MG, Kopp OR, Kim TH, von Arnim AG. Modular domain structure of Arabidopsis COP1. Reconstitution of activity by fragment complementation and mutational analysis of a nuclear localization signal in planta. PLANT PHYSIOLOGY 2000; 124:979-90. [PMID: 11080276 PMCID: PMC59198 DOI: 10.1104/pp.124.3.979] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2000] [Accepted: 06/08/2000] [Indexed: 05/21/2023]
Abstract
The Arabidopsis COP1 protein functions as a developmental regulator, in part by repressing photomorphogenesis in darkness. Using complementation of a cop1 loss-of-function allele with transgenes expressing fusions of cop1 mutant proteins and beta-glucuronidase, it was confirmed that COP1 consists of two modules, an amino terminal module conferring a basal function during development and a carboxyl terminal module conferring repression of photomorphogenesis. The amino-terminal zinc-binding domain of COP1 was indispensable for COP1 function. In contrast, the debilitating effects of site-directed mutations in the single nuclear localization signal of COP1 were partially compensated by high-level transgene expression. The carboxyl-terminal module of COP1, though unable to substantially ameliorate a cop1 loss-of-function allele on its own, was sufficient for conferring a light-quality-dependent hyperetiolation phenotype in the presence of wild-type COP1. Moreover, partial COP1 activity could be reconstituted in vivo from two non-covalently linked, complementary polypeptides that represent the two functional modules of COP1. Evidence is presented for efficient association of the two sub-fragments of the split COP1 protein in Arabidopsis and in a yeast two-hybrid assay.
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Affiliation(s)
- M G Stacey
- Department of Botany, The University of Tennessee, Knoxville, Tennessee 37996-1100, USA
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Nayak SK, Batra JK. Localization of the catalytic activity in restrictocin molecule by deletion mutagenesis. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:1777-83. [PMID: 10712610 DOI: 10.1046/j.1432-1327.2000.01176.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Restrictocin, produced by the fungus Aspergillus restrictus, is a highly specific ribonucleolytic toxin which cleaves a single phosphodiester bond between G4325 and A4326 in the 28S rRNA. It is a nonglycosylated, single-chain, basic protein of 149 amino acids. The putative catalytic site of restrictocin includes Tyr47, His49, Glu95, Arg120 and His136. To map the catalytic activity in the restrictocin molecule, and to study the role of N- and C-terminus in its activity, we have systematically deleted amino-acid residues from both the termini. Three N-terminal deletions removing 8, 15 and 30 amino acids, and three C-terminal deletions lacking 4, 6, and 11 amino acids were constructed. The deletion mutants were expressed in Escherichia coli, purified to homogeneity and functionally characterized. Removal of eight N-terminal or four C-terminal amino acids rendered restrictocin partially inactive, whereas any further deletions from either end resulted in the complete inactivation of the toxin. The study demonstrates that intact N- and C-termini are required for the optimum functional activity of restrictocin.
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Affiliation(s)
- S K Nayak
- Immunochemistry Laboratory, National Institute of Immunology, New Delhi, India
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Coll MG, Protasevich II, Torrent J, Ribó M, Lobachov VM, Makarov AA, Vilanova M. Valine 108, a chain-folding initiation site-belonging residue, crucial for the ribonuclease A stability. Biochem Biophys Res Commun 1999; 265:356-60. [PMID: 10558871 DOI: 10.1006/bbrc.1999.1672] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Thermal denaturation of bovine pancreatic ribonuclease A and a set of its single variants, carrying replacements of hydrophobic residues in the postulated 106-118 chain folding initiation site, has been studied by differential scanning calorimetry. Ribonuclease A variants undergo a two-state thermal transition denaturation except for those with replacement of valine 108. Most mutations cause a significant destabilization of the protein compared to the wild-type, thus demonstrating the importance of hydrophobic residues at the 106-118 region in maintaining the stability of the molecule. Among them, those of valine 108 promote the greatest (14-27 degrees C) destabilization of the molecule. Therefore, valine 108 plays a crucial role for ribonuclease A stability.
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Affiliation(s)
- M G Coll
- Laboratori d'Enginyeria de Proteïnes, Departament de Biologia, Facultat de Ciències, Universitat de Girona, Campus Montilivi, Girona, 17071, Spain
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44
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Moran LB, Schneider JP, Kentsis A, Reddy GA, Sosnick TR. Transition state heterogeneity in GCN4 coiled coil folding studied by using multisite mutations and crosslinking. Proc Natl Acad Sci U S A 1999; 96:10699-704. [PMID: 10485889 PMCID: PMC17946 DOI: 10.1073/pnas.96.19.10699] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have investigated the folding behavior of dimeric and covalently crosslinked versions of the 33-residue alpha-helical GCN4-p1 coiled coil derived from the leucine zipper region of the transcriptional activator GCN4. The effects of multisite substitutions indicate that folding occurs along multiple routes with nucleation sites located throughout the protein. The similarity in activation energies of the different routes together with an analysis of intrinsic helical propensities indicate that minimal helix is present before a productive collision of the two chains. However, approximately one-third to one-half of the total helical structure is formed in the postcollision transition state ensemble. For the crosslinked, monomeric version, folding occurs along a single robust pathway. Here, the region nearest the crosslink, with the least helical propensity, is structured in the transition state whereas the region farthest from the tether, with the most propensity, is completely unstructured. Hence, the existence of transition state heterogeneity and the selection of folding routes critically depend on chain topology.
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Affiliation(s)
- L B Moran
- Department of Biochemistry and Molecular Biology, University of Chicago, 920 East 58th Street, Chicago, IL 60637, USA
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