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Cisneros AF, Gagnon-Arsenault I, Dubé AK, Després PC, Kumar P, Lafontaine K, Pelletier JN, Landry CR. Epistasis between promoter activity and coding mutations shapes gene evolvability. SCIENCE ADVANCES 2023; 9:eadd9109. [PMID: 36735790 PMCID: PMC9897669 DOI: 10.1126/sciadv.add9109] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Accepted: 12/22/2022] [Indexed: 06/01/2023]
Abstract
The evolution of protein-coding genes proceeds as mutations act on two main dimensions: regulation of transcription level and the coding sequence. The extent and impact of the connection between these two dimensions are largely unknown because they have generally been studied independently. By measuring the fitness effects of all possible mutations on a protein complex at various levels of promoter activity, we show that promoter activity at the optimal level for the wild-type protein masks the effects of both deleterious and beneficial coding mutations. Mutations that are deleterious at low activity but masked at optimal activity are slightly destabilizing for individual subunits and binding interfaces. Coding mutations that increase protein abundance are beneficial at low expression but could potentially incur a cost at high promoter activity. We thereby demonstrate that promoter activity in interaction with protein properties can dictate which coding mutations are beneficial, neutral, or deleterious.
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Affiliation(s)
- Angel F. Cisneros
- Département de biochimie, de microbiologie et de bio-informatique, Faculté des sciences et de génie, Université Laval, G1V 0A6, Québec, Canada
- Institut de biologie intégrative et des systèmes, Université Laval, G1V 0A6, Québec, Canada
- PROTEO, Le regroupement québécois de recherche sur la fonction, l’ingénierie et les applications des protéines, Université Laval, G1V 0A6, Québec, Canada
- Centre de recherche sur les données massives, Université Laval, G1V 0A6, Québec, Canada
| | - Isabelle Gagnon-Arsenault
- Département de biochimie, de microbiologie et de bio-informatique, Faculté des sciences et de génie, Université Laval, G1V 0A6, Québec, Canada
- Institut de biologie intégrative et des systèmes, Université Laval, G1V 0A6, Québec, Canada
- PROTEO, Le regroupement québécois de recherche sur la fonction, l’ingénierie et les applications des protéines, Université Laval, G1V 0A6, Québec, Canada
- Centre de recherche sur les données massives, Université Laval, G1V 0A6, Québec, Canada
- Département de biologie, Faculté des sciences et de génie, Université Laval, G1V 0A6, Québec, Canada
| | - Alexandre K. Dubé
- Département de biochimie, de microbiologie et de bio-informatique, Faculté des sciences et de génie, Université Laval, G1V 0A6, Québec, Canada
- Institut de biologie intégrative et des systèmes, Université Laval, G1V 0A6, Québec, Canada
- PROTEO, Le regroupement québécois de recherche sur la fonction, l’ingénierie et les applications des protéines, Université Laval, G1V 0A6, Québec, Canada
- Centre de recherche sur les données massives, Université Laval, G1V 0A6, Québec, Canada
- Département de biologie, Faculté des sciences et de génie, Université Laval, G1V 0A6, Québec, Canada
| | - Philippe C. Després
- Département de biochimie, de microbiologie et de bio-informatique, Faculté des sciences et de génie, Université Laval, G1V 0A6, Québec, Canada
- Institut de biologie intégrative et des systèmes, Université Laval, G1V 0A6, Québec, Canada
- PROTEO, Le regroupement québécois de recherche sur la fonction, l’ingénierie et les applications des protéines, Université Laval, G1V 0A6, Québec, Canada
- Centre de recherche sur les données massives, Université Laval, G1V 0A6, Québec, Canada
| | - Pradum Kumar
- Département de biochimie, de microbiologie et de bio-informatique, Faculté des sciences et de génie, Université Laval, G1V 0A6, Québec, Canada
- Department of Biosciences and Bioengineering, Indian Institute of Technology Roorkee, Roorkee, 247667, India
| | - Kiana Lafontaine
- PROTEO, Le regroupement québécois de recherche sur la fonction, l’ingénierie et les applications des protéines, Université Laval, G1V 0A6, Québec, Canada
- Département de biochimie et de médecine moléculaire, Faculté de médecine, Université de Montréal, H3C 3J7, Montréal, Canada
| | - Joelle N. Pelletier
- PROTEO, Le regroupement québécois de recherche sur la fonction, l’ingénierie et les applications des protéines, Université Laval, G1V 0A6, Québec, Canada
- Département de biochimie et de médecine moléculaire, Faculté de médecine, Université de Montréal, H3C 3J7, Montréal, Canada
- Département de chimie, Faculté des arts et des sciences, Université de Montréal, H3C 3J7, Montréal, Canada
| | - Christian R. Landry
- Département de biochimie, de microbiologie et de bio-informatique, Faculté des sciences et de génie, Université Laval, G1V 0A6, Québec, Canada
- Institut de biologie intégrative et des systèmes, Université Laval, G1V 0A6, Québec, Canada
- PROTEO, Le regroupement québécois de recherche sur la fonction, l’ingénierie et les applications des protéines, Université Laval, G1V 0A6, Québec, Canada
- Centre de recherche sur les données massives, Université Laval, G1V 0A6, Québec, Canada
- Département de biologie, Faculté des sciences et de génie, Université Laval, G1V 0A6, Québec, Canada
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2
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Mhashal AR, Major DT. Temperature-Dependent Kinetic Isotope Effects in R67 Dihydrofolate Reductase from Path-Integral Simulations. J Phys Chem B 2021; 125:1369-1377. [PMID: 33522797 PMCID: PMC7883348 DOI: 10.1021/acs.jpcb.0c10318] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Revised: 01/05/2021] [Indexed: 11/28/2022]
Abstract
Calculation of temperature-dependent kinetic isotope effects (KIE) in enzymes presents a significant theoretical challenge. Additionally, it is not trivial to identify enzymes with available experimental accurate intrinsic KIEs in a range of temperatures. In the current work, we present a theoretical study of KIEs in the primitive R67 dihydrofolate reductase (DHFR) enzyme and compare with experimental work. The advantage of R67 DHFR is its significantly lower kinetic complexity compared to more evolved DHFR isoforms. We employ mass-perturbation-based path-integral simulations in conjunction with umbrella sampling and a hybrid quantum mechanics-molecular mechanics Hamiltonian. We obtain temperature-dependent KIEs in good agreement with experiments and ascribe the temperature-dependent KIEs primarily to zero-point energy effects. The active site in the primitive enzyme is found to be poorly preorganized, which allows excessive water access to the active site and results in loosely bound reacting ligands.
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Affiliation(s)
- Anil R. Mhashal
- Department of Chemistry and Institute
for Nanotechnology & Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Dan Thomas Major
- Department of Chemistry and Institute
for Nanotechnology & Advanced Materials, Bar-Ilan University, Ramat-Gan 52900, Israel
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3
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Mhashal AR, Pshetitsky Y, Cheatum CM, Kohen A, Major DT. Evolutionary Effects on Bound Substrate pKa in Dihydrofolate Reductase. J Am Chem Soc 2018; 140:16650-16660. [DOI: 10.1021/jacs.8b09089] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Anil R. Mhashal
- Department of Chemistry, Bar-Ilan University, Ramat-Gan 5290002, Israel
| | - Yaron Pshetitsky
- Department of Chemistry, Bar-Ilan University, Ramat-Gan 5290002, Israel
| | | | - Amnon Kohen
- Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Dan Thomas Major
- Department of Chemistry, Bar-Ilan University, Ramat-Gan 5290002, Israel
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4
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Amaral PDA, Autheman D, de Melo GD, Gouault N, Cupif JF, Goyard S, Dutra P, Coatnoan N, Cosson A, Monet D, Saul F, Haouz A, Uriac P, Blondel A, Minoprio P. Designed mono- and di-covalent inhibitors trap modeled functional motions for Trypanosoma cruzi proline racemase in crystallography. PLoS Negl Trop Dis 2018; 12:e0006853. [PMID: 30372428 PMCID: PMC6224121 DOI: 10.1371/journal.pntd.0006853] [Citation(s) in RCA: 4] [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: 05/11/2018] [Revised: 11/08/2018] [Accepted: 09/18/2018] [Indexed: 11/19/2022] Open
Abstract
Chagas disease, caused by Trypanosoma cruzi, affects millions of people in South America and no satisfactory therapy exists, especially for its life threatening chronic phase. We targeted the Proline Racemase of T. cruzi, which is present in all stages of the parasite life cycle, to discover new inhibitors against this disease. The first published crystal structures of the enzyme revealed that the catalytic site is too small to allow any relevant drug design. In previous work, to break through the chemical space afforded to virtual screening and drug design, we generated intermediate models between the open (ligand free) and closed (ligand bound) forms of the enzyme. In the present work, we co-crystallized the enzyme with the selected inhibitors and found that they were covalently bound to the catalytic cysteine residues in the active site, thus explaining why these compounds act as irreversible inhibitors. These results led us to the design of a novel, more potent specific inhibitor, NG-P27. Co-crystallization of this new inhibitor with the enzyme allowed us to confirm the predicted protein functional motions and further characterize the chemical mechanism. Hence, the catalytic Cys300 sulfur atom of the enzyme attacks the C2 carbon of the inhibitor in a coupled, regiospecific—stereospecific Michael reaction with trans-addition of a proton on the C3 carbon. Strikingly, the six different conformations of the catalytic site in the crystal structures reported in this work had key similarities to our intermediate models previously generated by inference of the protein functional motions. These crystal structures span a conformational interval covering roughly the first quarter of the opening mechanism, demonstrating the relevance of modeling approaches to break through chemical space in drug design. There is an urgent need to develop innovative medicines addressing neglected diseases, multi-drug resistance and other unmet therapeutic needs. To create new drug design opportunities, we attempted to exploit protein functional motions by using a rational approach to model structural intermediates of a therapeutic target. After successfully designing inhibitors based on modeled intermediates of T. Cruzi proline racemase, the determination of crystal structures of the target protein in complex with the inhibitors revealed conformations that were strikingly close to the predicted models. Thus, beyond the discovery of compounds establishing a novel mode of action that can lead to innovative treatments of Chagas disease, we illustrate how modeling protein functional motions can be exploited in a rational approach to create opportunities in drug design.
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Affiliation(s)
- Patricia de Aguiar Amaral
- Université de Rennes 1, Equipe Chimie organique et interfaces (CORINT), UMR 6226 Sciences Chimiques de Rennes, Rennes, France
| | - Delphine Autheman
- Institut Pasteur, Laboratoire des Processus Infectieux à Trypanosomatidés, Département Infection et Epidémiologie, Paris, France
| | - Guilherme Dias de Melo
- Institut Pasteur, Laboratoire des Processus Infectieux à Trypanosomatidés, Département Infection et Epidémiologie, Paris, France
| | - Nicolas Gouault
- Université de Rennes 1, Equipe Chimie organique et interfaces (CORINT), UMR 6226 Sciences Chimiques de Rennes, Rennes, France
| | - Jean-François Cupif
- Université de Rennes 1, Equipe Chimie organique et interfaces (CORINT), UMR 6226 Sciences Chimiques de Rennes, Rennes, France
| | - Sophie Goyard
- Institut Pasteur, Laboratoire des Processus Infectieux à Trypanosomatidés, Département Infection et Epidémiologie, Paris, France
| | - Patricia Dutra
- Institut Pasteur, Laboratoire des Processus Infectieux à Trypanosomatidés, Département Infection et Epidémiologie, Paris, France
| | - Nicolas Coatnoan
- Institut Pasteur, Laboratoire des Processus Infectieux à Trypanosomatidés, Département Infection et Epidémiologie, Paris, France
| | - Alain Cosson
- Institut Pasteur, Laboratoire des Processus Infectieux à Trypanosomatidés, Département Infection et Epidémiologie, Paris, France
| | - Damien Monet
- Institut Pasteur, Unité de Bioinformatique Structurale, Département de Biologie Structurale et Chimie, CNRS-UMR 3528, Paris, France
| | - Frederick Saul
- Institut Pasteur, Plateforme de Cristallographie, Département de Biologie Structurale et Chimie, CNRS-UMR 3528, Paris, France
| | - Ahmed Haouz
- Institut Pasteur, Plateforme de Cristallographie, Département de Biologie Structurale et Chimie, CNRS-UMR 3528, Paris, France
| | - Philippe Uriac
- Université de Rennes 1, Equipe Chimie organique et interfaces (CORINT), UMR 6226 Sciences Chimiques de Rennes, Rennes, France
- * E-mail: (PU); (AB); (PM)
| | - Arnaud Blondel
- Institut Pasteur, Unité de Bioinformatique Structurale, Département de Biologie Structurale et Chimie, CNRS-UMR 3528, Paris, France
- * E-mail: (PU); (AB); (PM)
| | - Paola Minoprio
- Institut Pasteur, Laboratoire des Processus Infectieux à Trypanosomatidés, Département Infection et Epidémiologie, Paris, France
- * E-mail: (PU); (AB); (PM)
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5
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Bhojane P, Duff MR, Bafna K, Agarwal P, Stanley C, Howell EE. Small Angle Neutron Scattering Studies of R67 Dihydrofolate Reductase, a Tetrameric Protein with Intrinsically Disordered N-Termini. Biochemistry 2017; 56:5886-5899. [PMID: 29020453 PMCID: PMC5678894 DOI: 10.1021/acs.biochem.7b00822] [Citation(s) in RCA: 5] [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: 08/23/2017] [Revised: 10/02/2017] [Indexed: 11/28/2022]
Abstract
R67 dihydrofolate reductase (DHFR) is a homotetramer with a single active site pore and no sequence or structural homology with chromosomal DHFRs. The R67 enzyme provides resistance to trimethoprim, an active site-directed inhibitor of Escherichia coli DHFR. Sixteen to twenty N-terminal amino acids are intrinsically disordered in the R67 dimer crystal structure. Chymotrypsin cleavage of 16 N-terminal residues results in an active enzyme with a decreased stability. The space sampled by the disordered N-termini of R67 DHFR was investigated using small angle neutron scattering. From a combined analysis using molecular dynamics and the program SASSIE ( http://www.smallangles.net/sassie/SASSIE_HOME.html ), the apoenzyme displays a radius of gyration (Rg) of 21.46 ± 0.50 Å. Addition of glycine betaine, an osmolyte, does not result in folding of the termini as the Rg increases slightly to 22.78 ± 0.87 Å. SASSIE fits of the latter SANS data indicate that the disordered N-termini sample larger regions of space and remain disordered, suggesting they might function as entropic bristles. Pressure perturbation calorimetry also indicated that the volume of R67 DHFR increases upon addition of 10% betaine and decreased at 20% betaine because of the dehydration of the protein. Studies of the hydration of full-length R67 DHFR in the presence of the osmolytes betaine and dimethyl sulfoxide find around 1250 water molecules hydrating the protein. Similar studies with truncated R67 DHFR yield around 400 water molecules hydrating the protein in the presence of betaine. The difference of ∼900 waters indicates the N-termini are well-hydrated.
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Affiliation(s)
- Purva
P. Bhojane
- Department
of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996-0840, United States
| | - Michael R. Duff
- Department
of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996-0840, United States
| | - Khushboo Bafna
- Genome
Science and Technology Program, University
of Tennessee, Knoxville, Tennessee 37996-0840, United States
| | - Pratul Agarwal
- Computer
Science and Mathematics Division, Oak Ridge
National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Christopher Stanley
- Biology
and Soft Matter Division, Oak Ridge National
Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Elizabeth E. Howell
- Department
of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996-0840, United States
- Genome
Science and Technology Program, University
of Tennessee, Knoxville, Tennessee 37996-0840, United States
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6
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Ebert MCCJC, Morley KL, Volpato JP, Schmitzer AR, Pelletier JN. Asymmetric mutations in the tetrameric R67 dihydrofolate reductase reveal high tolerance to active-site substitutions. Protein Sci 2014; 24:495-507. [PMID: 25401264 DOI: 10.1002/pro.2602] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 11/07/2014] [Accepted: 11/10/2014] [Indexed: 11/08/2022]
Abstract
Type II R67 dihydrofolate reductase (DHFR) is a bacterial plasmid-encoded enzyme that is intrinsically resistant to the widely-administered antibiotic trimethoprim. R67 DHFR is genetically and structurally unrelated to E. coli chromosomal DHFR and has an unusual architecture, in that four identical protomers form a single symmetrical active site tunnel that allows only one substrate binding/catalytic event at any given time. As a result, substitution of an active-site residue has as many as four distinct consequences on catalysis, constituting an atypical model of enzyme evolution. Although we previously demonstrated that no single residue of the native active site is indispensable for function, library selection here revealed a strong bias toward maintenance of two native protomers per mutated tetramer. A variety of such "half-native" tetramers were shown to procure native-like catalytic activity, with similar KM values but kcat values 5- to 33-fold lower, illustrating a high tolerance for active-site substitutions. The selected variants showed a reduced thermal stability (Tm ∼12°C lower), which appears to result from looser association of the protomers, but generally showed a marked increase in resilience to heat denaturation, recovering activity to a significantly greater extent than the variant with no active-site substitutions. Our results suggest that the presence of two native protomers in the R67 DHFR tetramer is sufficient to provide native-like catalytic rate and thus ensure cellular proliferation.
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Affiliation(s)
- Maximilian C C J C Ebert
- Département de Biochimie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7, Canada; PROTEO, the Québec Network for Protein Function, Structure and Engineering, Québec, Canada; CGCC, the Center for Green Chemistry and Catalysis, Montréal, Canada
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7
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Feng J, Grubbs J, Dave A, Goswami S, Horner CG, Howell EE. Radical redesign of a tandem array of four R67 dihydrofolate reductase genes yields a functional, folded protein possessing 45 substitutions. Biochemistry 2010; 49:7384-92. [PMID: 20684560 DOI: 10.1021/bi1005943] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
R67 dihydrofolate reductase (DHFR) is a plasmid-encoded, type II enzyme. Four monomers (78 amino acids long) assemble into a homotetramer possessing 222 symmetry. In previous studies, a tandem array of four R67 DHFR gene copies was fused in frame to generate a functional monomer named Quad1. This protein possessed the essential tertiary structure of the R67 "parent". To facilitate mutagenesis reactions, restriction enzyme sites were introduced in the tandem gene array. S59A and H362L mutations were also added to minimize possible folding topologies; this protein product, named Quad3, possesses 10 substitutions and is functional. Since R67 DHFR possesses a stable scaffold, a large jump in sequence space was performed by the further addition of 45 amino acid substitutions. The mutational design utilized alternate sequences from other type II DHFRs. In addition, most of the mutations were positioned on the surface of the protein as well as in the disordered N-terminal sequence, which serves as the linker between the fused domains. The resulting Quad4 protein is quite functional; however, it is less stable than Quad1, suffering a DeltaDeltaG loss of 5 kcal/mol at pH 5. One unexpected result was formation of Quad4 dimers and higher order oligomers at pH 8. R67 DHFR, and its derivative Quad proteins, possesses a robust scaffold, capable of withstanding introduction of >or=55 substitutions.
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Affiliation(s)
- Jian Feng
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996-0840, USA
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8
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Alonso H, Gready JE. Integron-sequestered dihydrofolate reductase: a recently redeployed enzyme. Trends Microbiol 2006; 14:236-42. [PMID: 16584884 DOI: 10.1016/j.tim.2006.03.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Revised: 03/01/2006] [Accepted: 03/21/2006] [Indexed: 11/21/2022]
Abstract
The introduction and wide use of antibacterial drugs has resulted in the emergence of resistant organisms. DfrB dihydrofolate reductase (DHFR) is a bacterial enzyme that is uniquely associated with mobile gene cassettes within integrons, and confers resistance to the drug trimethoprim. This enzyme has intrigued microbiologists since it was discovered more than thirty years ago because of its simple structure, enzymatic inefficiency and its virtual insensitivity to trimethoprim. Here, for the first time, a comprehensive discussion of genetic, evolutionary, structural and functional studies of this enzyme is presented together. This information supports the ideas that DfrB DHFR is a poorly adapted catalyst and has recently been recruited to perform a novel enzymatic activity in response to selective pressure.
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Affiliation(s)
- Hernán Alonso
- Division of Molecular Bioscience, John Curtin School of Medical Research, Australian National University, Canberra, ACT 0200, Australia
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9
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Howell EE. Searching sequence space: two different approaches to dihydrofolate reductase catalysis. Chembiochem 2005; 6:590-600. [PMID: 15812782 DOI: 10.1002/cbic.200400237] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
There are numerous examples of proteins that catalyze the same reaction while possessing different structures. This review focuses on two dihydrofolate reductases (DHFRs) that have disparate structures and discusses how the catalytic strategies of these two DHFRs are driven by their respective scaffolds. The two proteins are E. coli chromosomal DHFR (Ec DHFR) and a type II R-plasmid-encoded DHFR, typified by R67 DHFR. The former has been described as a very well evolved enzyme with an efficiency of 0.15, while the latter has been suggested to be a model for a "primitive" enzyme that has not yet been optimized by evolution. This comparison underlines what is important to catalysis in these two enzymes and concurrently highlights fundamental issues in enzyme catalysis.
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Affiliation(s)
- Elizabeth E Howell
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996-0840, USA.
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10
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Affiliation(s)
- Ivan M Kompis
- ARPIDA Ltd, Dammstrasse 36, 4142 Münchenstein, Switzerland
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11
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Schmitzer AR, Lépine F, Pelletier JN. Combinatorial exploration of the catalytic site of a drug-resistant dihydrofolate reductase: creating alternative functional configurations. Protein Eng Des Sel 2004; 17:809-19. [PMID: 15576381 DOI: 10.1093/protein/gzh090] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We have applied a global approach to enzyme active site exploration, where multiple mutations were introduced combinatorially at the active site of Type II R67 dihydrofolate reductase (R67 DHFR), creating numerous new active site environments within a constant framework. By this approach, we combinatorially modified all 16 principal amino acids that constitute the active site of this enzyme. This approach is fundamentally different from active site point mutation in that the native active site context is no longer accounted for. Among the 1536 combinatorially mutated active site variants of R67 DHFR we created, we selected and kinetically characterized three variants with highly altered active site compositions. We determined that they are of high fitness, as defined by a complex function consisting jointly of catalytic activity and resistance to trimethoprim. The k(cat) and K(M) values were similar to those for the native enzyme. The favourable Delta(DeltaG) values obtained (ranging from -0.72 to -1.08 kcal/mol) suggest that, despite their complex mutational pattern, no fundamental change in the catalytic mechanism has occurred. We illustrate that combinatorial active site mutagenesis can allow for the creation of compensatory mutations that could not be predicted and thus provides a route for more extensive exploration of functional sequence space than is allowed by point mutation.
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Affiliation(s)
- Andreea R Schmitzer
- Département de Chimie, Université de Montréal, C.P. 6128, Succursale Centre-ville, H3C 3J7, Montréal, Québec, Canada
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12
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Dam J, Blondel A. Effect of multiple symmetries on the association of R67 DHFR subunits bearing interfacial complementing mutations. Protein Sci 2004; 13:1-14. [PMID: 14691216 PMCID: PMC2286515 DOI: 10.1110/ps.03309504] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
It was shown previously that complementation could be a powerful mean to probe protein-protein interactions in the normally tetrameric R67 DHFR. Indeed, mixing complementing inactive dimeric mutants produced active heterotetramers. This approach turned a homo-oligomer into a hetero-oligomer and thus allowed the use of combinatorial assays, a subtle analysis of the association forces, and a precise determination of the equilibrium dissociation constants (K(D)) by titrimetry. However, for some of the complementing pairs, the experimental data implied multiple equilibria involving heterodimers, although no monomers could be detected. Thus, the reactions involved had to be identified to elaborate a suitable model to determine the K(D) of those pairs correctly. That model suggested that homodimers associated rapidly before the protomers could be redistributed in a multiple equilibrium system. Kinetic data confirmed that view. The association data at equilibrium were analyzed by multiple curve fitting with all plausible combinations of parameters. This gave a confidence interval for K(D) that is safer than the usual 67% or 90% confidence interval. Finally, the K(D) of one specific reaction, the dissociation of a heterotetramer with the relevant symmetry into two homodimers could be determined with the relevant model for each complementing pair, although multiple equilibria were present. These K(D) can thus be used as a set of references data to test and improve theoretical methods such as association free energy calculations.
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Affiliation(s)
- Julie Dam
- Unité de Repliement et Modélisation des Protéines (CNRS URA 2185), Institut Pasteur, Paris Cedex, France
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