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Morea V, Angelucci F, Tame JRH, Di Cera E, Bellelli A. Structural Basis of Sequential and Concerted Cooperativity. Biomolecules 2022; 12:biom12111651. [PMID: 36359000 PMCID: PMC9687781 DOI: 10.3390/biom12111651] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Revised: 10/31/2022] [Accepted: 11/03/2022] [Indexed: 11/09/2022] Open
Abstract
Allostery is a property of biological macromolecules featuring cooperative ligand binding and regulation of ligand affinity by effectors. The definition was introduced by Monod and Jacob in 1963, and formally developed as the "concerted model" by Monod, Wyman, and Changeux in 1965. Since its inception, this model of cooperativity was seen as distinct from and not reducible to the "sequential model" originally formulated by Pauling in 1935, which was developed further by Koshland, Nemethy, and Filmer in 1966. However, it is difficult to decide which model is more appropriate from equilibrium or kinetics measurements alone. In this paper, we examine several cooperative proteins whose functional behavior, whether sequential or concerted, is established, and offer a combined approach based on functional and structural analysis. We find that isologous, mostly helical interfaces are common in cooperative proteins regardless of their mechanism. On the other hand, the relative contribution of tertiary and quaternary structural changes, as well as the asymmetry in the liganded state, may help distinguish between the two mechanisms.
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Affiliation(s)
- Veronica Morea
- Institute of Molecular Biology and Pathology (IBPM), National Research Council of Italy (CNR) c/o Dipartimento di Scienze Biochimiche “A. Rossi Fanelli”, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy
| | - Francesco Angelucci
- Department of Life, Health, and Environmental Sciences, University of L’Aquila, Piazzale Salvatore Tommasi 1, 67100 L’Aquila, Italy
| | - Jeremy R. H. Tame
- Drug Design Laboratory, Graduate School of Medical Life Science, Yokohama City University, Tsurumi, Yokohama 230-0045, Japan
| | - Enrico Di Cera
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, MO 63104, USA
| | - Andrea Bellelli
- Dipartimento di Scienze Biochimiche “A. Rossi Fanelli”, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy
- Correspondence:
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Karamitros CS, Murray K, Winemiller B, Lamb C, Stone EM, D'Arcy S, Johnson KA, Georgiou G. Leveraging intrinsic flexibility to engineer enhanced enzyme catalytic activity. Proc Natl Acad Sci U S A 2022; 119:e2118979119. [PMID: 35658075 PMCID: PMC9191678 DOI: 10.1073/pnas.2118979119] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Accepted: 03/01/2022] [Indexed: 11/18/2022] Open
Abstract
Dynamic motions of enzymes occurring on a broad range of timescales play a pivotal role in all steps of the reaction pathway, including substrate binding, catalysis, and product release. However, it is unknown whether structural information related to conformational flexibility can be exploited for the directed evolution of enzymes with higher catalytic activity. Here, we show that mutagenesis of residues exclusively located at flexible regions distal to the active site of Homo sapiens kynureninase (HsKYNase) resulted in the isolation of a variant (BF-HsKYNase) in which the rate of the chemical step toward kynurenine was increased by 45-fold. Mechanistic pre–steady-state kinetic analysis of the wild type and the evolved enzyme shed light on the underlying effects of distal mutations (>10 Å from the active site) on the rate-limiting step of the catalytic cycle. Hydrogen-deuterium exchange coupled to mass spectrometry and molecular dynamics simulations revealed that the amino acid substitutions in BF-HsKYNase allosterically affect the flexibility of the pyridoxal-5′-phosphate (PLP) binding pocket, thereby impacting the rate of chemistry, presumably by altering the conformational ensemble and sampling states more favorable to the catalyzed reaction.
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Affiliation(s)
| | - Kyle Murray
- Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080
| | - Brent Winemiller
- Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712
| | - Candice Lamb
- Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712
| | - Everett M. Stone
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712
- Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712
- Department of Oncology, Dell Medical School, University of Texas at Austin, Austin, TX 78712
- LiveSTRONG Cancer Institutes, Dell Medical School, University of Texas at Austin, Austin, TX 78712
| | - Sheena D'Arcy
- Department of Chemistry and Biochemistry, University of Texas at Dallas, Richardson, TX 75080
| | - Kenneth A. Johnson
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712
| | - George Georgiou
- Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX 78712
- Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712
- Department of Oncology, Dell Medical School, University of Texas at Austin, Austin, TX 78712
- LiveSTRONG Cancer Institutes, Dell Medical School, University of Texas at Austin, Austin, TX 78712
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78712
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3
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Lei Z, Wang N, Tan H, Zheng J, Jia Z. Conformational Plasticity of the Active Site Entrance in E. coli Aspartate Transcarbamoylase and Its Implication in Feedback Regulation. Int J Mol Sci 2020; 21:ijms21010320. [PMID: 31947715 PMCID: PMC6981877 DOI: 10.3390/ijms21010320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2019] [Revised: 12/21/2019] [Accepted: 12/23/2019] [Indexed: 11/21/2022] Open
Abstract
Aspartate transcarbamoylase (ATCase) has been studied for decades and Escherichia coli ATCase is referred as a “textbook example” for both feedback regulation and cooperativity. However, several critical questions about the catalytic and regulatory mechanisms of E. coli ATCase remain unanswered, especially about its remote feedback regulation. Herein, we determined a structure of E. coli ATCase in which a key residue located (Arg167) at the entrance of the active site adopted an uncommon open conformation, representing the first wild-type apo-form E. coli ATCase holoenzyme that features this state. Based on the structure and our results of enzymatic characterization, as well as molecular dynamic simulations, we provide new insights into the feedback regulation of E. coli ATCase. We speculate that the binding of pyrimidines or purines would affect the hydrogen bond network at the interface of the catalytic and regulatory subunit, which would further influence the stability of the open conformation of Arg167 and the enzymatic activity of ATCase. Our results not only revealed the importance of the previously unappreciated open conformation of Arg167 in the active site, but also helped to provide rationalization for the mechanism of the remote feedback regulation of ATCase.
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Affiliation(s)
- Zhen Lei
- College of Chemistry, Beijing Normal University, Beijing 100875, China; (Z.L.); (N.W.); (H.T.)
| | - Nan Wang
- College of Chemistry, Beijing Normal University, Beijing 100875, China; (Z.L.); (N.W.); (H.T.)
- Jiangsu Key Laboratory of Brain Disease Bioinformation, Research Center for Biochemistry and Molecular Biology, Xuzhou Medical University, Xuzhou 221004, China
| | - Hongwei Tan
- College of Chemistry, Beijing Normal University, Beijing 100875, China; (Z.L.); (N.W.); (H.T.)
| | - Jimin Zheng
- College of Chemistry, Beijing Normal University, Beijing 100875, China; (Z.L.); (N.W.); (H.T.)
- Correspondence: (J.Z.); (Z.J.); Tel.: +86-010-58806002 (J.Z.); +1-613-5336277 (Z.J.)
| | - Zongchao Jia
- Department of Biomedical and Molecular Sciences, Queen’s University, Kingston, ON K7L3N6, Canada
- Correspondence: (J.Z.); (Z.J.); Tel.: +86-010-58806002 (J.Z.); +1-613-5336277 (Z.J.)
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4
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BEES: Bayesian Ensemble Estimation from SAS. Biophys J 2019; 117:399-407. [PMID: 31337549 DOI: 10.1016/j.bpj.2019.06.024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Revised: 06/04/2019] [Accepted: 06/20/2019] [Indexed: 11/22/2022] Open
Abstract
Many biomolecular complexes exist in a flexible ensemble of states in solution that is necessary to perform their biological function. Small-angle scattering (SAS) measurements are a popular method for characterizing these flexible molecules because of their relative ease of use and their ability to simultaneously probe the full ensemble of states. However, SAS data is typically low dimensional and difficult to interpret without the assistance of additional structural models. In theory, experimental SAS curves can be reconstituted from a linear combination of theoretical models, although this procedure carries a significant risk of overfitting the inherently low-dimensional SAS data. Previously, we developed a Bayesian-based method for fitting ensembles of model structures to experimental SAS data that rigorously avoids overfitting. However, we have found that these methods can be difficult to incorporate into typical SAS modeling workflows, especially for users that are not experts in computational modeling. To this end, we present the Bayesian Ensemble Estimation from SAS (BEES) program. Two forks of BEES are available, the primary one existing as a module for the SASSIE web server and a developmental version that is a stand-alone Python program. BEES allows users to exhaustively sample ensemble models constructed from a library of theoretical states and to interactively analyze and compare each model's performance. The fitting routine also allows for secondary data sets to be supplied, thereby simultaneously fitting models to both SAS data as well as orthogonal information. The flexible ensemble of K63-linked ubiquitin trimers is presented as an example of BEES' capabilities.
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Abstract
X-ray scattering is uniquely suited to the study of disordered systems and thus has the potential to provide insight into dynamic processes where diffraction methods fail. In particular, while X-ray crystallography has been a staple of structural biology for more than half a century and will continue to remain so, a major limitation of this technique has been the lack of dynamic information. Solution X-ray scattering has become an invaluable tool in structural and mechanistic studies of biological macromolecules where large conformational changes are involved. Such systems include allosteric enzymes that play key roles in directing metabolic fluxes of biochemical pathways, as well as large, assembly-line type enzymes that synthesize secondary metabolites with pharmaceutical applications. Furthermore, crystallography has the potential to provide information on protein dynamics via the diffuse scattering patterns that are overlaid with Bragg diffraction. Historically, these patterns have been very difficult to interpret, but recent advances in X-ray detection have led to a renewed interest in diffuse scattering analysis as a way to probe correlated motions. Here, we will review X-ray scattering theory and highlight recent advances in scattering-based investigations of protein solutions and crystals, with a particular focus on complex enzymes.
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Affiliation(s)
- Steve P Meisburger
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
| | - William C Thomas
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
| | - Maxwell B Watkins
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
| | - Nozomi Ando
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
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Abstract
Allostery is a ubiquitous biological regulatory process in which distant binding sites within a protein or enzyme are functionally and thermodynamically coupled. Allosteric interactions play essential roles in many enzymological mechanisms, often facilitating formation of enzyme-substrate complexes and/or product release. Thus, elucidating the forces that drive allostery is critical to understanding the complex transformations of biomolecules. Currently, a number of models exist to describe allosteric behavior, taking into account energetics as well as conformational rearrangements and fluctuations. In the following Review, we discuss the use of solution NMR techniques designed to probe allosteric mechanisms in enzymes. NMR spectroscopy is unequaled in its ability to detect structural and dynamical changes in biomolecules, and the case studies presented herein demonstrate the range of insights to be gained from this valuable method. We also provide a detailed technical discussion of several specialized NMR experiments that are ideally suited for the study of enzymatic allostery.
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Affiliation(s)
- George P. Lisi
- Department of Chemistry, Yale University, New Haven, CT 06520
| | - J. Patrick Loria
- Department of Chemistry, Yale University, New Haven, CT 06520
- Department of Molecular Biophysics & Biochemistry, Yale University, New Haven, CT 06520
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7
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Ikehara Y, Arai K, Furukawa N, Ohno T, Miyake T, Fushinobu S, Nakajima M, Miyanaga A, Taguchi H. The core of allosteric motion in Thermus caldophilus L-lactate dehydrogenase. J Biol Chem 2014; 289:31550-64. [PMID: 25258319 DOI: 10.1074/jbc.m114.599092] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
For Thermus caldophilus L-lactate dehydrogenase (TcLDH), fructose 1,6-bisphosphate (FBP) reduced the pyruvate S(0.5) value 10(3)-fold and increased the V(max) value 4-fold at 30 °C and pH 7.0, indicating that TcLDH has a much more T state-sided allosteric equilibrium than Thermus thermophilus L-lactate dehydrogenase, which has only two amino acid replacements, A154G and H179Y. The inactive (T) and active (R) state structures of TcLDH were determined at 1.8 and 2.0 Å resolution, respectively. The structures indicated that two mobile regions, MR1 (positions 172-185) and MR2 (positions 211-221), form a compact core for allosteric motion, and His(179) of MR1 forms constitutive hydrogen bonds with MR2. The Q4(R) mutation, which comprises the L67E, H68D, E178K, and A235R replacements, increased V(max) 4-fold but reduced pyruvate S(0.5) only 5-fold in the reaction without FBP. In contrast, the P2 mutation, comprising the R173Q and R216L replacements, did not markedly increase V(max), but 10(2)-reduced pyruvate S(0.5), and additively increased the FBP-independent activity of the Q4(R) enzyme. The two types of mutation consistently increased the thermal stability of the enzyme. The MR1-MR2 area is a positively charged cluster, and its center approaches another positively charged cluster (N domain cluster) across the Q-axis subunit interface by 5 Å, when the enzyme undergoes the T to R transition. Structural and kinetic analyses thus revealed the simple and unique allosteric machinery of TcLDH, where the MR1-MR2 area pivotally moves during the allosteric motion and mediates the allosteric equilibrium through electrostatic repulsion within the protein molecule.
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Affiliation(s)
- Yoko Ikehara
- From the Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
| | - Kazuhito Arai
- From the Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
| | - Nayuta Furukawa
- From the Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
| | - Tadashi Ohno
- From the Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
| | - Tatsuya Miyake
- From the Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
| | - Shinya Fushinobu
- the Department of Biotechnology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan, and
| | - Masahiro Nakajima
- From the Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
| | - Akimasa Miyanaga
- the Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8551, Japan
| | - Hayao Taguchi
- From the Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan,
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8
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Cockrell GM, Zheng Y, Guo W, Peterson AW, Truong JK, Kantrowitz ER. New paradigm for allosteric regulation of Escherichia coli aspartate transcarbamoylase. Biochemistry 2013; 52:8036-47. [PMID: 24138583 DOI: 10.1021/bi401205n] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
For nearly 60 years, the ATP activation and the CTP inhibition of Escherichia coli aspartate transcarbamoylase (ATCase) has been the textbook example of allosteric regulation. We present kinetic data and five X-ray structures determined in the absence and presence of a Mg(2+) concentration within the physiological range. In the presence of 2 mM divalent cations (Mg(2+), Ca(2+), Zn(2+)), CTP does not significantly inhibit the enzyme, while the allosteric activation by ATP is enhanced. The data suggest that the actual allosteric inhibitor of ATCase in vivo is the combination of CTP, UTP, and a divalent cation, and the actual allosteric activator is a divalent cation with ATP or ATP and GTP. The structural data reveals that two NTPs can bind to each allosteric site with a divalent cation acting as a bridge between the triphosphates. Thus, the regulation of ATCase is far more complex than previously believed and calls many previous studies into question. The X-ray structures reveal that the catalytic chains undergo essentially no alternations; however, several regions of the regulatory chains undergo significant structural changes. Most significant is that the N-terminal region of the regulatory chains exists in different conformations in the allosterically activated and inhibited forms of the enzyme. Here, a new model of allosteric regulation is proposed.
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Affiliation(s)
- Gregory M Cockrell
- Department of Chemistry, Boston College , Merkert Chemistry Center, 2609 Beacon Street, Chestnut Hill, MA 02467 U.S.A
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Joseph TT, Osman R. Convergent transmission of RNAi guide-target mismatch information across Argonaute internal allosteric network. PLoS Comput Biol 2012; 8:e1002693. [PMID: 23028290 PMCID: PMC3459882 DOI: 10.1371/journal.pcbi.1002693] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Accepted: 07/28/2012] [Indexed: 11/19/2022] Open
Abstract
In RNA interference, a guide strand derived from a short dsRNA such as a microRNA (miRNA) is loaded into Argonaute, the central protein in the RNA Induced Silencing Complex (RISC) that silences messenger RNAs on a sequence-specific basis. The positions of any mismatched base pairs in an miRNA determine which Argonaute subtype is used. Subsequently, the Argonaute-guide complex binds and silences complementary target mRNAs; certain Argonautes cleave the target. Mismatches between guide strand and the target mRNA decrease cleavage efficiency. Thus, loading and silencing both require that signals about the presence of a mismatched base pair are communicated from the mismatch site to effector sites. These effector sites include the active site, to prevent target cleavage; the binding groove, to modify nucleic acid binding affinity; and surface allosteric sites, to control recruitment of additional proteins to form the RISC. To examine how such signals may be propagated, we analyzed the network of internal allosteric pathways in Argonaute exhibited through correlations of residue-residue interactions. The emerging network can be described as a set of pathways emanating from the core of the protein near the active site, distributed into the bulk of the protein, and converging upon a distributed cluster of surface residues. Nucleotides in the guide strand "seed region" have a stronger relationship with the protein than other nucleotides, concordant with their importance in sequence selectivity. Finally, any of several seed region guide-target mismatches cause certain Argonaute residues to have modified correlations with the rest of the protein. This arises from the aggregation of relatively small interaction correlation changes distributed across a large subset of residues. These residues are in effector sites: the active site, binding groove, and surface, implying that direct functional consequences of guide-target mismatches are mediated through the cumulative effects of a large number of internal allosteric pathways.
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Affiliation(s)
- Thomas T. Joseph
- Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, New York, United States of America
- Computational Biology Program, New York University, New York, New York, United States of America
| | - Roman Osman
- Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, New York, United States of America
- Computational Biology Program, New York University, New York, New York, United States of America
- * E-mail:
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10
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Lilyestrom WG, Shire SJ, Scherer TM. Influence of the cosolute environment on IgG solution structure analyzed by small-angle X-ray scattering. J Phys Chem B 2012; 116:9611-8. [PMID: 22827493 PMCID: PMC3774592 DOI: 10.1021/jp303839t] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Small-angle X-ray scattering experiments of two monoclonal antibodies (mAbs) were performed as a function of Hofmeister salt type and concentration including 100 mM Na(2)SO(4), 100-600 mM of NaSCN, or 100-600 mM arginine chloride at pH 6.0 to yield information on the effects of cosolutes on mAb solution conformation and flexibility. Minimal selected ensemble (MSE) procedures used to reconstruct the SAXS form factors revealed that both IgG1 mAbs exist in a conformational equilibrium with two subpopulations that vary in overall shape and size. The "closed" mAb conformation is characterized by a maximum dimension of ∼155 Å and shorter distances between Fab-Fab and Fab-FC domains. The "open" mAb conformation has a maximum dimension of ∼175 Å and an increase in the interdomain distances with concomitant increases in overall mAb flexibility. Analysis of the distribution of shapes and sizes of mAb structures within the conformational equilibrium indicates that they remain essentially unchanged under conditions with a broad range of chaotropic and kosmotropic salts including 100-600 mM NaSCN and 100 mM Na(2)SO(4). Analysis of the conformations within each MSE population under various conditions reveals a striking similarity between many of the MSE structures, IgG crystal structures, and single-molecule imaging studies; MSE analysis of mAb form factors also identified an overall relaxation of the mAb structure unique to solution conditions containing arginine chloride, characterized by an increased maximum dimension and a shift toward the population of the "open" mAb conformation. Our results provide the first comprehensive characterization of mAb conformational diversity in solution and are of direct relevance to understanding the effects of solution conditions on protein structural dynamics and stability.
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Affiliation(s)
- Wayne G Lilyestrom
- Genentech, Late Stage Pharmaceutical Development, 1 DNA Way, South San Francisco, California 94080, United States
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11
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Trapping and structure determination of an intermediate in the allosteric transition of aspartate transcarbamoylase. Proc Natl Acad Sci U S A 2012; 109:7741-6. [PMID: 22547808 DOI: 10.1073/pnas.1119683109] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
X-ray crystallography and small-angle X-ray scattering (SAXS) in solution have been used to show that a mutant aspartate transcarbamoylase exists in an intermediate quaternary structure between the canonical T and R structures. Additionally, the SAXS data indicate a pH-dependent structural alteration consistent with either a pH-induced conformational change or a pH-induced alteration in the T to R equilibrium. These data indicate that this mutant is not a model for the R state, as has been proposed, but rather represents the enzyme trapped along the path of the allosteric transition between the T and R states.
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12
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Asciutto EK, Young MJ, Madura J, Pochapsky SS, Pochapsky TC. Solution structural ensembles of substrate-free cytochrome P450(cam). Biochemistry 2012; 51:3383-93. [PMID: 22468842 DOI: 10.1021/bi300007r] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Removal of substrate (+)-camphor from the active site of cytochrome P450(cam) (CYP101A1) results in nuclear magnetic resonance-detected perturbations in multiple regions of the enzyme. The (1)H-(15)N correlation map of substrate-free diamagnetic Fe(II) CO-bound CYP101A permits these perturbations to be mapped onto the solution structure of the enzyme. Residual dipolar couplings (RDCs) were measured for (15)N-(1)H amide pairs in two independent alignment media for the substrate-free enzyme and used as restraints in solvated molecular dynamics (MD) simulations to generate an ensemble of best-fit structures of the substrate-free enzyme in solution. Nuclear magnetic resonance-detected chemical shift perturbations reflect changes in the electronic environment of the NH pairs, such as hydrogen bonding and ring current shifts, and are observed for residues in the active site as well as in hinge regions between secondary structural features. RDCs provide information about relative orientations of secondary structures, and RDC-restrained MD simulations indicate that portions of a β-rich region adjacent to the active site shift so as to partially occupy the vacancy left by removal of the substrate. The accessible volume of the active site is reduced in the substrate-free enzyme relative to the substrate-bound structure calculated using the same methods. Both symmetric and asymmetric broadening of multiple resonances observed upon substrate removal as well as localized increased errors in RDC fits suggest that an ensemble of enzyme conformations are present in the substrate-free form.
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Affiliation(s)
- Eliana K Asciutto
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282-1530, USA
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13
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Lipscomb WN, Kantrowitz ER. Structure and mechanisms of Escherichia coli aspartate transcarbamoylase. Acc Chem Res 2012; 45:444-53. [PMID: 22011033 DOI: 10.1021/ar200166p] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Enzymes catalyze a particular reaction in cells, but only a few control the rate of this reaction and the metabolic pathway that follows. One specific mechanism for such enzymatic control of a metabolic pathway involves molecular feedback, whereby a metabolite further down the pathway acts at a unique site on the control enzyme to alter its activity allosterically. This regulation may be positive or negative (or both), depending upon the particular system. Another method of enzymatic control involves the cooperative binding of the substrate, which allows a large change in enzyme activity to emanate from only a small change in substrate concentration. Allosteric regulation and homotropic cooperativity are often known to involve significant conformational changes in the structure of the protein. Escherichia coli aspartate transcarbamoylase (ATCase) is the textbook example of an enzyme that regulates a metabolic pathway, namely, pyrimidine nucleotide biosynthesis, by feedback control and by the cooperative binding of the substrate, L-aspartate. The catalytic and regulatory mechanisms of this enzyme have been extensively studied. A series of X-ray crystal structures of the enzyme in the presence and absence of substrates, products, and analogues have provided details, at the molecular level, of the conformational changes that the enzyme undergoes as it shifts between its low-activity, low-affinity form (T state) to its high-activity, high-affinity form (R state). These structural data provide insights into not only how this enzyme catalyzes the reaction between l-aspartate and carbamoyl phosphate to form N-carbamoyl-L-aspartate and inorganic phosphate, but also how the allosteric effectors modulate this activity. In this Account, we summarize studies on the structure of the enzyme and describe how these structural data provide insights into the catalytic and regulatory mechanisms of the enzyme. The ATCase-catalyzed reaction is regulated by nucleotide binding some 60 Å from the active site, inducing structural alterations that modulate catalytic activity. The delineation of the structure and function in this particular model system will help in understanding the molecular basis of cooperativity and allosteric regulation in other systems as well.
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Affiliation(s)
- William N. Lipscomb
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Evan R. Kantrowitz
- Department of Chemistry, Boston College, Merkert Chemistry Center, Chestnut Hill, Massachusetts 02467-3860, United States
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14
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Abstract
The Monod-Wyman-Changeux (MWC) model was conceived in 1965 to account for the signal transduction and cooperative properties of bacterial regulatory enzymes and hemoglobin. It was soon extended to pharmacological receptors for neurotransmitters and other macromolecular entities involved in intracellular and intercellular communications. Five decades later, the two main hypotheses of the model are reexamined on the basis of a variety of regulatory proteins with known X-ray structures: (a) Regulatory proteins possess an oligomeric structure with symmetry properties, and (b) the allosteric interactions between topographically distinct sites are mediated by a conformational transition established between a few preestablished states with conservation of symmetry and ligand-directed conformational selection. Several well-documented examples are adequately represented by the MWC model, yet a few possible exceptions are noted. New questions are raised concerning the dynamics of the allosteric transitions and more complex supramolecular ensembles.
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Affiliation(s)
- Jean-Pierre Changeux
- Collège de France & Institut Pasteur, URA CNRS 2182, Paris Cedex 15 75724, France.
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15
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Allostery and cooperativity in Escherichia coli aspartate transcarbamoylase. Arch Biochem Biophys 2011; 519:81-90. [PMID: 22198283 DOI: 10.1016/j.abb.2011.10.024] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2011] [Revised: 10/27/2011] [Accepted: 10/28/2011] [Indexed: 11/20/2022]
Abstract
The allosteric enzyme aspartate transcarbamoylase (ATCase) from Escherichia coli has been the subject of investigations for approximately 50 years. This enzyme controls the rate of pyrimidine nucleotide biosynthesis by feedback inhibition, and helps to balance the pyrimidine and purine pools by competitive allosteric activation by ATP. The catalytic and regulatory components of the dodecameric enzyme can be separated and studied independently. Many of the properties of the enzyme follow the Monod, Wyman Changeux model of allosteric control thus E. coli ATCase has become the textbook example. This review will highlight kinetic, biophysical, and structural studies which have provided a molecular level understanding of how the allosteric nature of this enzyme regulates pyrimidine nucleotide biosynthesis.
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16
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Lee J, Goodey NM. Catalytic contributions from remote regions of enzyme structure. Chem Rev 2011; 111:7595-624. [PMID: 21923192 DOI: 10.1021/cr100042n] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Jeeyeon Lee
- Department of Chemistry, 413 Wartik Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
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17
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Changeux JP, Edelstein S. Conformational selection or induced fit? 50 years of debate resolved. F1000 BIOLOGY REPORTS 2011; 3:19. [PMID: 21941598 PMCID: PMC3169905 DOI: 10.3410/b3-19] [Citation(s) in RCA: 183] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Exactly 50 years ago, biochemists raised the question of the mechanism of the conformational change that mediates “allosteric” interactions between regulatory sites and biologically active sites in regulatory/receptor proteins. Do the different conformations involved already exist spontaneously in the absence of the regulatory ligands (Monod-Wyman-Changeux), such that the complementary protein conformation would be selected to mediate signal transduction, or do particular ligands induce the receptor to adopt the conformation best suited to them (Koshland-Nemethy-Filmer—induced fit)? This is not just a central question for biophysics, it also has enormous importance for drug design. Recent advances in techniques have allowed detailed experimental and theoretical comparisons with the formal models of both scenarios. Also, it has been shown that mutated receptors can adopt constitutively active confirmations in the absence of ligand. There have also been demonstrations that the atomic resolution structures of the same protein are essentially the same whether ligand is bound or not. These and other advances in past decades have produced a situation where the vast majority of the data using different categories of regulatory proteins (including regulatory enzymes, ligand-gated ion channels, G protein-coupled receptors, and nuclear receptors) support the conformational selection scheme of signal transduction.
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Affiliation(s)
- Jean-Pierre Changeux
- Collège de France and Institut PasteurCNRS URA 2182, 25 rue du Dr Roux, 75015 ParisFrance
| | - Stuart Edelstein
- European Bioinformatics Institute and University of GenevaWellcome Trust Genome Campus, Hinxton, CB10 1SDUK
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18
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Niu W, Chen Z, Gandhi PS, Vogt AD, Pozzi N, Pelc LA, Zapata F, Di Cera E. Crystallographic and kinetic evidence of allostery in a trypsin-like protease. Biochemistry 2011; 50:6301-7. [PMID: 21707111 DOI: 10.1021/bi200878c] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Protein allostery is based on the existence of multiple conformations in equilibrium linked to distinct functional properties. Although evidence of allosteric transitions is relatively easy to identify by functional studies, structural detection of a pre-existing equilibrium between alternative conformations remains challenging even for textbook examples of allosteric proteins. Kinetic studies show that the trypsin-like protease thrombin exists in equilibrium between two conformations where the active site is either collapsed (E*) or accessible to substrate (E). However, structural demonstration that the two conformations exist in the same enzyme construct free of ligands has remained elusive. Here we report the crystal structure of the thrombin mutant N143P in the E form, which complements the recently reported structure in the E* form, and both the E and E* forms of the thrombin mutant Y225P. The side chain of W215 moves 10.9 Å between the two forms, causing a displacement of 6.6 Å of the entire 215-217 segment into the active site that in turn opens or closes access to the primary specificity pocket. Rapid kinetic measurements of p-aminobenzamidine binding to the active site confirm the existence of the E*-E equilibrium in solution for wild-type and the mutants N143P and Y225P. These findings provide unequivocal proof of the allosteric nature of thrombin and lend strong support to the recent proposal that the E*-E equilibrium is a key property of the trypsin fold.
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Affiliation(s)
- Weiling Niu
- Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104, USA
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19
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Protein functional landscapes, dynamics, allostery: a tortuous path towards a universal theoretical framework. Q Rev Biophys 2010; 43:295-332. [DOI: 10.1017/s0033583510000119] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
AbstractEnergy landscape theories have provided a common ground for understanding the protein folding problem, which once seemed to be overwhelmingly complicated. At the same time, the native state was found to be an ensemble of interconverting states with frustration playing a more important role compared to the folding problem. The landscape of the folded protein – the native landscape – is glassier than the folding landscape; hence, a general description analogous to the folding theories is difficult to achieve. On the other hand, the native basin phase volume is much smaller, allowing a protein to fully sample its native energy landscape on the biological timescales. Current computational resources may also be used to perform this sampling for smaller proteins, to build a ‘topographical map’ of the native landscape that can be used for subsequent analysis. Several major approaches to representing this topographical map are highlighted in this review, including the construction of kinetic networks, hierarchical trees and free energy surfaces with subsequent structural and kinetic analyses. In this review, we extensively discuss the important question of choosing proper collective coordinates characterizing functional motions. In many cases, the substates on the native energy landscape, which represent different functional states, can be used to obtain variables that are well suited for building free energy surfaces and analyzing the protein's functional dynamics. Normal mode analysis can provide such variables in cases where functional motions are dictated by the molecule's architecture. Principal component analysis is a more expensive way of inferring the essential variables from the protein's motions, one that requires a long molecular dynamics simulation. Finally, the two popular models for the allosteric switching mechanism, ‘preexisting equilibrium’ and ‘induced fit’, are interpreted within the energy landscape paradigm as extreme points of a continuum of transition mechanisms. Some experimental evidence illustrating each of these two models, as well as intermediate mechanisms, is presented and discussed.
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20
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Bahar I, Lezon TR, Yang LW, Eyal E. Global dynamics of proteins: bridging between structure and function. Annu Rev Biophys 2010; 39:23-42. [PMID: 20192781 DOI: 10.1146/annurev.biophys.093008.131258] [Citation(s) in RCA: 446] [Impact Index Per Article: 31.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Biomolecular systems possess unique, structure-encoded dynamic properties that underlie their biological functions. Recent studies indicate that these dynamic properties are determined to a large extent by the topology of native contacts. In recent years, elastic network models used in conjunction with normal mode analyses have proven to be useful for elucidating the collective dynamics intrinsically accessible under native state conditions, including in particular the global modes of motions that are robustly defined by the overall architecture. With increasing availability of structural data for well-studied proteins in different forms (liganded, complexed, or free), there is increasing evidence in support of the correspondence between functional changes in structures observed in experiments and the global motions predicted by these coarse-grained analyses. These observed correlations suggest that computational methods may be advantageously employed for assessing functional changes in structure and allosteric mechanisms intrinsically favored by the native fold.
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Affiliation(s)
- Ivet Bahar
- Department of Computational Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.
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21
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Mertens HDT, Svergun DI. Structural characterization of proteins and complexes using small-angle X-ray solution scattering. J Struct Biol 2010; 172:128-41. [PMID: 20558299 DOI: 10.1016/j.jsb.2010.06.012] [Citation(s) in RCA: 384] [Impact Index Per Article: 27.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2010] [Revised: 06/08/2010] [Accepted: 06/10/2010] [Indexed: 01/27/2023]
Abstract
Small-angle scattering of X-rays (SAXS) is an established method for the low-resolution structural characterization of biological macromolecules in solution. The technique provides three-dimensional low-resolution structures, using ab initio and rigid body modeling, and allow one to assess the oligomeric state of proteins and protein complexes. In addition, SAXS is a powerful tool for structure validation and the quantitative analysis of flexible systems, and is highly complementary to the high resolution methods of X-ray crystallography and NMR. At present, SAXS analysis methods have reached an advanced state, allowing for automated and rapid characterization of protein solutions in terms of low-resolution models, quaternary structure and oligomeric composition. In this communication, main approaches to the characterization of proteins and protein complexes using SAXS are reviewed. The tools for the analysis of proteins in solution are presented, and the impact that these tools have made in modern structural biology is discussed.
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Affiliation(s)
- Haydyn D T Mertens
- European Molecular Biology Laboratory-Hamburg Outstation, c/o DESY, Notkestrasse 85, Hamburg, Germany
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22
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Ligand depletion in vivo modulates the dynamic range and cooperativity of signal transduction. PLoS One 2010; 5:e8449. [PMID: 20052284 PMCID: PMC2797075 DOI: 10.1371/journal.pone.0008449] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Accepted: 11/27/2009] [Indexed: 11/19/2022] Open
Abstract
Biological signal transduction commonly involves cooperative interactions in the binding of ligands to their receptors. In many cases, ligand concentrations in vivo are close to the value of the dissociation constant of their receptors, resulting in the phenomenon of ligand depletion. Using examples based on rotational bias of bacterial flagellar motors and calcium binding to mammalian calmodulin, we show that ligand depletion diminishes cooperativity and broadens the dynamic range of sensitivity to the signaling ligand. As a result, the same signal transducer responds to different ranges of signal with various degrees of cooperativity according to its effective cellular concentration. Hence, results from in vitro dose-response analyses cannot be applied directly to understand signaling in vivo. Moreover, the receptor concentration is revealed to be a key element in controlling signal transduction and we propose that its modulation constitutes a new way of controlling sensitivity to signals. In addition, through an analysis of the allosteric enzyme aspartate transcarbamylase, we demonstrate that the classical Hill coefficient is not appropriate for characterizing the change in conformational state upon ligand binding to an oligomeric protein (equivalent to a dose-response curve), because it ignores the cooperativity of the conformational change for the corresponding equivalent monomers, which are generally characterized by a Hill coefficient . Therefore, we propose a new index of cooperativity based on the comparison of the properties of oligomers and their equivalent monomers.
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23
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Effect of interdomain dynamics on the structure determination of modular proteins by small-angle scattering. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:769-80. [DOI: 10.1007/s00249-009-0549-3] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2009] [Revised: 09/10/2009] [Accepted: 09/24/2009] [Indexed: 01/08/2023]
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24
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Whitley MJ, Lee AL. Frameworks for understanding long-range intra-protein communication. Curr Protein Pept Sci 2009; 10:116-27. [PMID: 19355979 DOI: 10.2174/138920309787847563] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The phenomenon of intra-protein communication is fundamental to such processes as allostery and signaling, yet comparatively little is understood about its physical origins despite notable progress in recent years. This review introduces contemporary but distinct frameworks for understanding intra-protein communication by presenting both the ideas behind them and a discussion of their successes and shortcomings. The first framework holds that intra-protein communication is accomplished by the sequential mechanical linkage of residues spanning a gap between distal sites. According to the second framework, proteins are best viewed as ensembles of distinct structural microstates, the dynamical and thermodynamic properties of which contribute to the experimentally observable macroscale properties. Nuclear magnetic resonance (NMR) spectroscopy is a powerful method for studying intra-protein communication, and the insights into both frameworks it provides are presented through a discussion of numerous examples from the literature. Distinct from mechanical and thermodynamic considerations of intra-protein communication are recently applied graph and network theoretic analyses. These computational methods reduce complex three dimensional protein architectures to simple maps comprised of nodes (residues) connected by edges (inter-residue "interactions"). Analysis of these graphs yields a characterization of the protein's topology and network characteristics. These methods have shown proteins to be "small world" networks with moderately high local residue connectivities existing concurrently with a small but significant number of long range connectivities. However, experimental studies of the tantalizing idea that these putative long range interaction pathways facilitate one or several macroscopic protein characteristics are unfortunately lacking at present. This review concludes by comparing and contrasting the presented frameworks and methodologies for studying intra-protein communication and suggests a manner in which they can be brought to bear simultaneously to further enhance our understanding of this important fundamental phenomenon.
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Affiliation(s)
- Matthew J Whitley
- Department of Biochemistry & Biophysics, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA
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25
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Allosteric communication occurs via networks of tertiary and quaternary motions in proteins. PLoS Comput Biol 2009; 5:e1000293. [PMID: 19229311 PMCID: PMC2634971 DOI: 10.1371/journal.pcbi.1000293] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 01/09/2009] [Indexed: 11/19/2022] Open
Abstract
Allosteric proteins bind an effector molecule at one site resulting in a functional change at a second site. We hypothesize that allosteric communication in proteins relies upon networks of quaternary (collective, rigid-body) and tertiary (residue-residue contact) motions. We argue that cyclic topology of these networks is necessary for allosteric communication. An automated algorithm identifies rigid bodies from the displacement between the inactive and the active structures and constructs "quaternary networks" from these rigid bodies and the substrate and effector ligands. We then integrate quaternary networks with a coarse-grained representation of contact rearrangements to form "global communication networks" (GCNs). The GCN reveals allosteric communication among all substrate and effector sites in 15 of 18 multidomain and multimeric proteins, while tertiary and quaternary networks exhibit such communication in only 4 and 3 of these proteins, respectively. Furthermore, in 7 of the 15 proteins connected by the GCN, 50% or more of the substrate-effector paths via the GCN are "interdependent" paths that do not exist via either the tertiary or the quaternary network. Substrate-effector "pathways" typically are not linear but rather consist of polycyclic networks of rigid bodies and clusters of rearranging residue contacts. These results argue for broad applicability of allosteric communication based on structural changes and demonstrate the utility of the GCN. Global communication networks may inform a variety of experiments on allosteric proteins as well as the design of allostery into non-allosteric proteins.
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26
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West JM, Xia J, Tsuruta H, Guo W, O'Day EM, Kantrowitz ER. Time evolution of the quaternary structure of Escherichia coli aspartate transcarbamoylase upon reaction with the natural substrates and a slow, tight-binding inhibitor. J Mol Biol 2008; 384:206-18. [PMID: 18823998 DOI: 10.1016/j.jmb.2008.09.022] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2008] [Revised: 09/08/2008] [Accepted: 09/09/2008] [Indexed: 11/30/2022]
Abstract
Here, we present a study of the conformational changes of the quaternary structure of Escherichia coli aspartate transcarbamoylase, as monitored by time-resolved small-angle X-ray scattering, upon combining with substrates, substrate analogs, and nucleotide effectors at temperatures between 5 and 22 degrees C, obviating the need for ethylene glycol. Time-resolved small-angle X-ray scattering time courses tracking the T-->R structural change after mixing with substrates or substrate analogs appeared to be a single phase under some conditions and biphasic under other conditions, which we ascribe to multiple ligation states producing a time course composed of multiple rates. Increasing the concentration of substrates up to a certain point increased the T-->R transition rate, with no further increase in rate beyond that point. Most strikingly, after addition of N-phosphonacetyl-l-aspartate to the enzyme, the transition rate was more than 1 order of magnitude slower than with the natural substrates. These results on the homotropic mechanism are consistent with a concerted transition between structural and functional states of either low affinity, low activity or high affinity, high activity for aspartate. Addition of ATP along with the substrates increased the rate of the transition from the T to the R state and also decreased the duration of the R-state steady-state phase. Addition of CTP or the combination of CTP/UTP to the substrates significantly decreased the rate of the T-->R transition and caused a shift in the enzyme population towards the T state even at saturating substrate concentrations. These results on the heterotropic mechanism suggest a destabilization of the T state by ATP and a destabilization of the R state by CTP and CTP/UTP, consistent with the T and R state crystallographic structures of aspartate transcarbamoylase in the presence of the heterotropic effectors.
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Affiliation(s)
- Jay M West
- Department of Chemistry, Boston College, Merkert Chemistry Center, Chestnut Hill, MA 02467-3807, USA
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27
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Datta D, Scheer JM, Romanowski MJ, Wells JA. An allosteric circuit in caspase-1. J Mol Biol 2008; 381:1157-67. [PMID: 18590738 DOI: 10.1016/j.jmb.2008.06.040] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2008] [Revised: 06/10/2008] [Accepted: 06/12/2008] [Indexed: 12/11/2022]
Abstract
Structural studies of caspase-1 reveal that the dimeric thiol protease can exist in two states: in an on-state, when the active site is occupied, or in an off-state, when the active site is empty or when the enzyme is bound by a synthetic allosteric ligand at the dimer interface approximately 15 A from the active site. A network of 21 hydrogen bonds from nine side chains connecting the active and allosteric sites change partners when going between the on-state and the off-state. Alanine-scanning mutagenesis of these nine side chains shows that only two of them-Arg286 and Glu390, which form a salt bridge-have major effects, causing 100- to 200-fold reductions in catalytic efficiency (k(cat)/K(m)). Two neighbors, Ser332 and Ser339, have minor effects, causing 4- to 7-fold reductions. A more detailed mutational analysis reveals that the enzyme is especially sensitive to substitutions of the salt bridge: even a homologous R286K substitution causes a 150-fold reduction in k(cat)/K(m). X-ray crystal structures of these variants suggest the importance of both the salt bridge interaction and the coordination of solvent water molecules near the allosteric binding pocket. Thus, only a small subset of side chains from the larger hydrogen bonding network is critical for activity. These form a contiguous set of interactions that run from one active site through the allosteric site at the dimer interface and onto the second active site. This subset constitutes a functional allosteric circuit or "hot wire" that promotes site-to-site coupling.
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Affiliation(s)
- Debajyoti Datta
- Departments of Pharmaceutical Chemistry and Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, CA 94143, USA
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28
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Rabinowitz JD, Hsiao JJ, Gryncel KR, Kantrowitz ER, Feng XJ, Li G, Rabitz H. Dissecting enzyme regulation by multiple allosteric effectors: nucleotide regulation of aspartate transcarbamoylase. Biochemistry 2008; 47:5881-8. [PMID: 18454556 DOI: 10.1021/bi8000566] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The enzyme aspartate transcarbamoylase (ATCase, EC 2.1.3.2 of Escherichia coli), which catalyzes the committed step of pyrimidine biosynthesis, is allosterically regulated by all four ribonucleoside triphosphates (NTPs) in a nonlinear manner. Here, we dissect this regulation using the recently developed approach of random sampling-high-dimensional model representation (RS-HDMR). ATCase activity was measured in vitro at 300 random NTP concentration combinations, each involving (consistent with in vivo conditions) all four NTPs being present. These data were then used to derive a RS-HDMR model of ATCase activity over the full four-dimensional NTP space. The model accounted for 90% of the variance in the experimental data. Its main elements were positive ATCase regulation by ATP and negative by CTP, with the negative effects of CTP dominating the positive ones of ATP when both regulators were abundant (i.e., a negative cooperative effect of ATP x CTP). Strong sensitivity to both ATP and CTP concentrations occurred in their physiological concentration ranges. UTP had only a slight effect, and GTP had almost none. These findings support a predominant role of CTP and ATP in ATCase regulation. The general approach provides a new paradigm for dissecting multifactorial regulation of biological molecules and processes.
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Affiliation(s)
- Joshua D Rabinowitz
- Department of Chemistry, Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey 08544, USA.
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29
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Tsai CJ, Sol AD, Nussinov R. Allostery: absence of a change in shape does not imply that allostery is not at play. J Mol Biol 2008; 378:1-11. [PMID: 18353365 PMCID: PMC2684958 DOI: 10.1016/j.jmb.2008.02.034] [Citation(s) in RCA: 361] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2007] [Revised: 02/15/2008] [Accepted: 02/15/2008] [Indexed: 11/17/2022]
Abstract
Allostery is essential for controlled catalysis, signal transmission, receptor trafficking, turning genes on and off, and apoptosis. It governs the organism's response to environmental and metabolic cues, dictating transient partner interactions in the cellular network. Textbooks taught us that allostery is a change of shape at one site on the protein surface brought about by ligand binding to another. For several years, it has been broadly accepted that the change of shape is not induced; rather, it is observed simply because a larger protein population presents it. Current data indicate that while side chains can reorient and rewire, allostery may not even involve a change of (backbone) shape. Assuming that the enthalpy change does not reverse the free-energy change due to the change in entropy, entropy is mainly responsible for binding.
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Affiliation(s)
- Chung-Jung Tsai
- Basic Research Program, SAIC-Frederick, Inc., Center for Cancer Research Nanobiology Program, NCI-Frederick, Frederick, MD 21702
| | - Antonio del Sol
- Bioinformatics Research Unit, Research and Development Division, Fujirebio Inc., 51 Komiya-cho, Hachioji-shi, Tokyo 192-0031, Japan
| | - Ruth Nussinov
- Basic Research Program, SAIC-Frederick, Inc., Center for Cancer Research Nanobiology Program, NCI-Frederick, Frederick, MD 21702
- Sackler Inst. of Molecular Medicine, Department of Human Genetics and Molecular Medicine, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
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30
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Keskin O, Gursoy A, Ma B, Nussinov R. Principles of Protein−Protein Interactions: What are the Preferred Ways For Proteins To Interact? Chem Rev 2008; 108:1225-44. [DOI: 10.1021/cr040409x] [Citation(s) in RCA: 476] [Impact Index Per Article: 29.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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31
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Bernadó P, Pérez Y, Svergun DI, Pons M. Structural Characterization of the Active and Inactive States of Src Kinase in Solution by Small-Angle X-ray Scattering. J Mol Biol 2008; 376:492-505. [DOI: 10.1016/j.jmb.2007.11.066] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2007] [Revised: 11/15/2007] [Accepted: 11/21/2007] [Indexed: 11/29/2022]
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32
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Koch MHJ, Bras W. Synchrotron radiation studies of non-crystalline systems. ACTA ACUST UNITED AC 2008. [DOI: 10.1039/b703892p] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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33
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Intrinsic dynamics of enzymes in the unbound state and relation to allosteric regulation. Curr Opin Struct Biol 2007; 17:633-40. [PMID: 18024008 DOI: 10.1016/j.sbi.2007.09.011] [Citation(s) in RCA: 248] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2007] [Revised: 08/21/2007] [Accepted: 09/28/2007] [Indexed: 11/23/2022]
Abstract
In recent years, there has been a surge in the number of studies exploring the relationship between proteins' equilibrium dynamics and structural changes involved in function. An emerging concept, supported by both theory and experiments, is that under native state conditions proteins have an intrinsic ability to sample conformations that meet functional requirements. A typical example is the ability of enzymes to sample open and closed forms, irrespective of substrate, succeeded by the stabilization of one form (usually closed) upon substrate binding. This ability is structure-encoded, and plays a key role in facilitating allosteric regulation, which suggests complementing the sequence-encodes-structure paradigm of protein science by structure-encodes-dynamics-encodes-function. The emerging connection implies an evolutionary role in selecting/conserving structures based on their ability to achieve functional dynamics, and in turn, selecting sequences that fold into such 'apt' structures.
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34
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Wang J, Eldo J, Kantrowitz ER. Structural model of the R state of Escherichia coli aspartate transcarbamoylase with substrates bound. J Mol Biol 2007; 371:1261-73. [PMID: 17603076 PMCID: PMC2720131 DOI: 10.1016/j.jmb.2007.06.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2007] [Revised: 06/01/2007] [Accepted: 06/05/2007] [Indexed: 01/07/2023]
Abstract
The allosteric enzyme aspartate transcarbamoylase (ATCase) exists in two conformational states. The enzyme, in the absence of substrates is primarily in the low-activity T state, is converted to the high-activity R state upon substrate binding, and remains in the R state until substrates are exhausted. These conformational changes have made it difficult to obtain structural data on R-state active-site complexes. Here we report the R-state structure of ATCase with the substrate Asp and the substrate analog phosphonoactamide (PAM) bound. This R-state structure represents the stage in the catalytic mechanism immediately before the formation of the covalent bond between the nitrogen of the amino group of Asp and the carbonyl carbon of carbamoyl phosphate. The binding mode of the PAM is similar to the binding mode of the phosphonate moiety of N-(phosphonoacetyl)-l-aspartate (PALA), the carboxylates of Asp interact with the same residues that interact with the carboxylates of PALA, although the position and orientations are shifted. The amino group of Asp is 2.9 A away from the carbonyl oxygen of PAM, positioned correctly for the nucleophilic attack. Arg105 and Leu267 in the catalytic chain interact with PAM and Asp and help to position the substrates correctly for catalysis. This structure fills a key gap in the structural determination of each of the steps in the catalytic cycle. By combining these data with previously determined structures we can now visualize the allosteric transition through detailed atomic motions that underlie the molecular mechanism.
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Affiliation(s)
- Jie Wang
- Department of Chemistry, Boston College, Merkert Chemistry Center, Chestnut Hill, MA 02467
| | - Joby Eldo
- Department of Chemistry, Boston College, Merkert Chemistry Center, Chestnut Hill, MA 02467
| | - Evan R. Kantrowitz
- Department of Chemistry, Boston College, Merkert Chemistry Center, Chestnut Hill, MA 02467
- E-mail address of corresponding author:
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