1
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Juretić D, Bonačić Lošić Ž. Theoretical Improvements in Enzyme Efficiency Associated with Noisy Rate Constants and Increased Dissipation. ENTROPY (BASEL, SWITZERLAND) 2024; 26:151. [PMID: 38392406 PMCID: PMC10888251 DOI: 10.3390/e26020151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 01/18/2024] [Accepted: 02/05/2024] [Indexed: 02/24/2024]
Abstract
Previous studies have revealed the extraordinarily large catalytic efficiency of some enzymes. High catalytic proficiency is an essential accomplishment of biological evolution. Natural selection led to the increased turnover number, kcat, and enzyme efficiency, kcat/KM, of uni-uni enzymes, which convert a single substrate into a single product. We added or multiplied random noise with chosen rate constants to explore the correlation between dissipation and catalytic efficiency for ten enzymes: beta-galactosidase, glucose isomerase, β-lactamases from three bacterial strains, ketosteroid isomerase, triosephosphate isomerase, and carbonic anhydrase I, II, and T200H. Our results highlight the role of biological evolution in accelerating thermodynamic evolution. The catalytic performance of these enzymes is proportional to overall entropy production-the main parameter from irreversible thermodynamics. That parameter is also proportional to the evolutionary distance of β-lactamases PC1, RTEM, and Lac-1 when natural or artificial evolution produces the optimal or maximal possible catalytic efficiency. De novo enzyme design and attempts to speed up the rate-limiting catalytic steps may profit from the described connection between kinetics and thermodynamics.
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Affiliation(s)
- Davor Juretić
- Mediterranean Institute for Life Sciences, Šetalište Ivana Meštrovića 45, 21000 Split, Croatia
- Faculty of Science, University of Split, Ruđera Boškovića 33, 21000 Split, Croatia
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2
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Jiang Y, Ding N, Shao Q, Stull SL, Cheng Z, Yang ZJ. Substrate Positioning Dynamics Involves a Non-Electrostatic Component to Mediate Catalysis. J Phys Chem Lett 2023; 14:11480-11489. [PMID: 38085952 PMCID: PMC11211065 DOI: 10.1021/acs.jpclett.3c02444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2023]
Abstract
Substrate positioning dynamics (SPD) orients the substrate in the active site, thereby influencing catalytic efficiency. However, it remains unknown whether SPD effects originate primarily from electrostatic perturbation inside the enzyme or can independently mediate catalysis with a significant non-electrostatic component. In this work, we investigated how the non-electrostatic component of SPD affects transition state (TS) stabilization. Using high-throughput enzyme modeling, we selected Kemp eliminase variants with similar electrostatics inside the enzyme but significantly different SPD. The kinetic parameters of these mutants were experimentally characterized. We observed a valley-shaped, two-segment linear correlation between the TS stabilization free energy (converted from kinetic parameters) and substrate positioning index (a metric to quantify SPD). The energy varies by approximately 2 kcal/mol. Favorable SPD was observed for the distal mutant R154W, increasing the proportion of reactive conformations and leading to the lowest activation free energy. These results indicate the substantial contribution of the non-electrostatic component of SPD to enzyme catalytic efficiency.
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Affiliation(s)
- Yaoyukun Jiang
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Ning Ding
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Qianzhen Shao
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Sebastian L. Stull
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Zihao Cheng
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Zhongyue J. Yang
- Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States
- Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37235, United States
- Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee 37235, United States
- Data Science Institute, Vanderbilt University, Nashville, Tennessee 37235, United States
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, Tennessee 37235, United States
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3
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Kazan IC, Mills JH, Ozkan SB. Allosteric regulatory control in dihydrofolate reductase is revealed by dynamic asymmetry. Protein Sci 2023; 32:e4700. [PMID: 37313628 PMCID: PMC10357497 DOI: 10.1002/pro.4700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 06/05/2023] [Accepted: 06/06/2023] [Indexed: 06/15/2023]
Abstract
We investigated the relationship between mutations and dynamics in Escherichia coli dihydrofolate reductase (DHFR) using computational methods. Our study focused on the M20 and FG loops, which are known to be functionally important and affected by mutations distal to the loops. We used molecular dynamics simulations and developed position-specific metrics, including the dynamic flexibility index (DFI) and dynamic coupling index (DCI), to analyze the dynamics of wild-type DHFR and compared our results with existing deep mutational scanning data. Our analysis showed a statistically significant association between DFI and mutational tolerance of the DHFR positions, indicating that DFI can predict functionally beneficial or detrimental substitutions. We also applied an asymmetric version of our DCI metric (DCIasym ) to DHFR and found that certain distal residues control the dynamics of the M20 and FG loops, whereas others are controlled by them. Residues that are suggested to control the M20 and FG loops by our DCIasym metric are evolutionarily nonconserved; mutations at these sites can enhance enzyme activity. On the other hand, residues controlled by the loops are mostly deleterious to function when mutated and are also evolutionary conserved. Our results suggest that dynamics-based metrics can identify residues that explain the relationship between mutation and protein function or can be targeted to rationally engineer enzymes with enhanced activity.
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Affiliation(s)
- I. Can Kazan
- Center for Biological Physics and Department of PhysicsArizona State UniversityTempeArizonaUSA
| | - Jeremy H. Mills
- School of Molecular Sciences and The Biodesign Center for Molecular Design and BiomimeticsArizona State UniversityTempeArizonaUSA
| | - S. Banu Ozkan
- Center for Biological Physics and Department of PhysicsArizona State UniversityTempeArizonaUSA
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4
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Liu AK, Pereira JH, Kehl AJ, Rosenberg DJ, Orr DJ, Chu SKS, Banda DM, Hammel M, Adams PD, Siegel JB, Shih PM. Structural plasticity enables evolution and innovation of RuBisCO assemblies. SCIENCE ADVANCES 2022; 8:eadc9440. [PMID: 36026446 PMCID: PMC9417184 DOI: 10.1126/sciadv.adc9440] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Accepted: 07/13/2022] [Indexed: 06/15/2023]
Abstract
Oligomerization is a core structural feature that defines the form and function of many proteins. Most proteins form molecular complexes; however, there remains a dearth of diversity-driven structural studies investigating the evolutionary trajectory of these assemblies. Ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) is one such enzyme that adopts multiple assemblies, although the origins and distribution of its different oligomeric states remain cryptic. Here, we retrace the evolution of ancestral and extant form II RuBisCOs, revealing a complex and diverse history of oligomerization. We structurally characterize a newly discovered tetrameric RuBisCO, elucidating how solvent-exposed surfaces can readily adopt new interactions to interconvert or give rise to new oligomeric states. We further use these principles to engineer and demonstrate how changes in oligomerization can be mediated by relatively few mutations. Our findings yield insight into how structural plasticity may give rise to new oligomeric states.
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Affiliation(s)
- Albert K. Liu
- Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA 94720, USA
- Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Biochemistry, Molecular, Cellular and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616, USA
| | - Jose H. Pereira
- Technology Division, Joint BioEnergy Institute, Emeryville, CA 94608, USA
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Alexander J. Kehl
- Biophysics Graduate Group, University of California, Davis, Davis, CA, USA
| | - Daniel J. Rosenberg
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
- Graduate Group in Biophysics, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Douglas J. Orr
- Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
| | - Simon K. S. Chu
- Biophysics Graduate Group, University of California, Davis, Davis, CA, USA
| | - Douglas M. Banda
- Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Michal Hammel
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Paul D. Adams
- Technology Division, Joint BioEnergy Institute, Emeryville, CA 94608, USA
- Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
- Department of Bioengineering, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Justin B. Siegel
- Genome Center, University of California, Davis, Davis, CA 95616, USA
- Chemistry Department, University of California, Davis, Davis, CA 95616, USA
- Department of Biochemistry and Molecular Medicine, University of California, Sacramento, Sacramento, CA 95616, USA
| | - Patrick M. Shih
- Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA 94720, USA
- Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
- Feedstocks Division, Joint BioEnergy Institute, Emeryville, CA 94608, USA
- Innovative Genomics Institute, University of California, Berkeley, Berkeley, CA 94720, USA
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5
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Benkovic SJ. From Bioorganic Models to Cells. Annu Rev Biochem 2021; 90:57-76. [PMID: 34153218 DOI: 10.1146/annurev-biochem-062320-062929] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
I endeavor to share how various choices-some deliberate, some unconscious-and the unmistakable influence of many others shaped my scientific pursuits. I am fascinated by how two long-term, major streams of my research, DNA replication and purine biosynthesis, have merged with unexpected interconnections. If I have imparted to many of the talented individuals who have passed through my lab a degree of my passion for uncloaking the mysteries hidden in scientific research and an understanding of the honesty and rigor it demands and its impact on the world community, then my mentorship has been successful.
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Affiliation(s)
- Stephen J Benkovic
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA;
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6
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Wang X, Zhang X, Peng C, Shi Y, Li H, Xu Z, Zhu W. D3DistalMutation: a Database to Explore the Effect of Distal Mutations on Enzyme Activity. J Chem Inf Model 2021; 61:2499-2508. [PMID: 33938221 DOI: 10.1021/acs.jcim.1c00318] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Enzyme activity is affected by amino acid mutations, particularly mutations near the active site. Increasing evidence has shown that distal mutations more than 10 Å away from the active site may significantly affect enzyme activity. However, it is difficult to study the enzyme regulation mechanism of distal mutations due to the lack of a systematic collection of three-dimensional (3D) structures, highlighting distal mutation site and the corresponding enzyme activity change. Therefore, we constructed a distal mutation database, namely, D3DistalMutation, which relates the distal mutation to enzyme activity. As a result, we observed that approximately 80% of distal mutations could affect enzyme activity and 72.7% of distal mutations would decrease or abolish enzyme activity in D3DistalMutation. Only 6.6% of distal mutations in D3DistalMutation could increase enzyme activity, which have great potential to the industrial field. Among these mutations, the Y to F, S to D, and T to D mutations are most likely to increase enzyme activity, which sheds some light on industrial catalysis. Distal mutations decreasing enzyme activity in the allosteric pocket play an indispensable role in allosteric drug design. In addition, the pockets in the enzyme structures are provided to explore the enzyme regulation mechanism of distal mutations. D3DistalMutation is accessible free of charge at https://www.d3pharma.com/D3DistalMutation/index.php.
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Affiliation(s)
- Xiaoyu Wang
- CAS Key Laboratory of Receptor Research; Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.,College of Mathematics and Physics, Shanghai University of Electric Power, Shanghai 200090, China
| | - Xinben Zhang
- CAS Key Laboratory of Receptor Research; Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Cheng Peng
- CAS Key Laboratory of Receptor Research; Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Yulong Shi
- CAS Key Laboratory of Receptor Research; Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Huiyu Li
- College of Mathematics and Physics, Shanghai University of Electric Power, Shanghai 200090, China
| | - Zhijian Xu
- CAS Key Laboratory of Receptor Research; Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Weiliang Zhu
- CAS Key Laboratory of Receptor Research; Drug Discovery and Design Center, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
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7
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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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8
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Bhat AS, Dustin Schaeffer R, Kinch L, Medvedev KE, Grishin NV. Recent advances suggest increased influence of selective pressure in allostery. Curr Opin Struct Biol 2020; 62:183-188. [PMID: 32302874 DOI: 10.1016/j.sbi.2020.02.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Revised: 02/21/2020] [Accepted: 02/25/2020] [Indexed: 12/19/2022]
Abstract
Allosteric regulation of protein functions is ubiquitous in organismal biology, but the principles governing its evolution are not well understood. Here we discuss recent studies supporting the large-scale existence of latent allostery in ancestor proteins of superfamilies. As suggested, the evolution of allostery could be driven by the need for specificity in paralogs of slow evolving protein complexes with conserved active sites. The same slow evolution is displayed by purifying selection exhibited in allosteric proteins with somatic mutations involved in cancer, where disease-associated mutations are enriched in both orthosteric and allosteric sites. Consequently, disease-associated variants can be used to identify druggable allosteric sites that are specific for paralogs in protein superfamilies with otherwise similar functions.
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Affiliation(s)
- Archana S Bhat
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9050, United States
| | - Richard Dustin Schaeffer
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9050, United States
| | - Lisa Kinch
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390-9050, United States
| | - Kirill E Medvedev
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9050, United States
| | - Nick V Grishin
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390-9050, United States; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390-9050, United States.
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9
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Xu H, Liang W, Ning L, Jiang Y, Yang W, Wang C, Qi F, Ma L, Du L, Fourage L, Zhou YJ, Li S. Directed Evolution of P450 Fatty Acid Decarboxylases via High‐Throughput Screening towards Improved Catalytic Activity. ChemCatChem 2019. [DOI: 10.1002/cctc.201901347] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Huifang Xu
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
| | - Weinan Liang
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
- University of Chinese Academy of Sciences Beijing 100049 P. R. China
| | - Linlin Ning
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
- University of Chinese Academy of Sciences Beijing 100049 P. R. China
| | - Yuanyuan Jiang
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
- University of Chinese Academy of Sciences Beijing 100049 P. R. China
| | - Wenxia Yang
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
| | - Cong Wang
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
| | - Feifei Qi
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
| | - Li Ma
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
- State Key Laboratory of Microbial TechnologyShandong University Shandong 266237 P. R. China
| | - Lei Du
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
| | | | - Yongjin J. Zhou
- Division of Biotechnology Dalian Institute of Chemical Physics (DICP)Chinese Academy of Sciences Dalian 116023 P. R. China
| | - Shengying Li
- Shandong Provincial Key Laboratory of Synthetic Biology CAS Key Laboratory of Biofuels Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of Sciences Shandong 266101 P. R. China
- State Key Laboratory of Microbial TechnologyShandong University Shandong 266237 P. R. China
- Laboratory for Marine Biology and BiotechnologyQingdao National Laboratory for Marine Science and Technology Shandong 266237 P. R. China
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10
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Li J, Fortunato G, Lin J, Agarwal PK, Kohen A, Singh P, Cheatum CM. Evolution Conserves the Network of Coupled Residues in Dihydrofolate Reductase. Biochemistry 2019; 58:3861-3868. [PMID: 31423766 PMCID: PMC7296831 DOI: 10.1021/acs.biochem.9b00460] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Understanding protein motions and their role in enzymatic reactions is an important and timely topic in enzymology. Protein motions that are involved in the chemical step of catalysis are particularly intriguing but difficult to identify. A global network of coupled residues in Escherichia coli dihydrofolate reductase (E. coli DHFR), which assists in catalyzing the chemical step, has previously been demonstrated through quantum mechanical/molecular mechanical and molecular dynamics simulations as well as bioinformatic analyses. A few specific residues (M42, G121, F125, and I14) were shown to function synergistically with measurements of single-turnover rates and the temperature dependence of intrinsic kinetic isotope effects (KIEsint) of site-directed mutants. This study hypothesizes that the global network of residues involved in the chemical step is evolutionarily conserved and probes homologous residues of the potential global network in human DHFR through measurements of the temperature dependence of KIEsint and computer simulations based on the empirical valence bond method. We study mutants M53W and S145V. Both of these remote residues are homologous to network residues in E. coli DHFR. Non-additive isotope effects on activation energy are observed between M53 and S145, indicating their synergistic effect on the chemical step in human DHFR, which suggests that both of these residues are part of a network affecting the chemical step in enzyme catalysis. This finding supports the hypothesis that human and E. coli DHFR share similar networks, consistent with evolutionary preservation of such networks.
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Affiliation(s)
- Jiayue Li
- Department of Chemistry, University of Iowa, Iowa City, IA 52242
| | | | - Jennifer Lin
- Department of Chemistry, University of Iowa, Iowa City, IA 52242
| | - Pratul K. Agarwal
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996
| | - Amnon Kohen
- Department of Chemistry, University of Iowa, Iowa City, IA 52242
| | - Priyanka Singh
- Department of Chemistry, University of Iowa, Iowa City, IA 52242
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11
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Smith IN, Thacker S, Seyfi M, Cheng F, Eng C. Conformational Dynamics and Allosteric Regulation Landscapes of Germline PTEN Mutations Associated with Autism Compared to Those Associated with Cancer. Am J Hum Genet 2019; 104:861-878. [PMID: 31006514 PMCID: PMC6506791 DOI: 10.1016/j.ajhg.2019.03.009] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2018] [Accepted: 03/08/2019] [Indexed: 01/07/2023] Open
Abstract
Individuals with germline PTEN tumor-suppressor variants have PTEN hamartoma tumor syndrome (PHTS). Clinically, PHTS has variable presentations; there are distinct subsets of PHTS-affected individuals, such as those diagnosed with autism spectrum disorder (ASD) or cancer. It remains unclear why mutations in one gene can lead to such seemingly disparate phenotypes. Therefore, we sought to determine whether it is possible to predict a given PHTS-affected individual's a priori risk of ASD, cancer, or the co-occurrence of both phenotypes. By integrating network proximity analysis performed on the human interactome, molecular simulations, and residue-interaction networks, we demonstrate the role of conformational dynamics in the structural communication and long-range allosteric regulation of germline PTEN variants associated with ASD or cancer. We show that the PTEN interactome shares significant overlap with the ASD and cancer interactomes, providing network-based evidence that PTEN is a crucial player in the biology of both disorders. Importantly, this finding suggests that a germline PTEN variant might perturb the ASD or cancer networks differently, thus favoring one disease outcome at any one time. Furthermore, protein-dynamic structural-network analysis reveals small-world structural communication mediated by highly conserved functional residues and potential allosteric regulation of PTEN. We identified a salient structural-communication pathway that extends across the inter-domain interface for cancer-only mutations. In contrast, the structural-communication pathway is predominantly restricted to the phosphatase domain for ASD-only mutations. Our integrative approach supports the prediction and potential modulation of the relevant conformational states that influence structural communication and long-range perturbations associated with mutational effects that lead to PTEN-ASD or PTEN-cancer phenotypes.
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Affiliation(s)
- Iris Nira Smith
- Genomic Medicine Institute, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
| | - Stetson Thacker
- Genomic Medicine Institute, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA; Cleveland Clinic Lerner College of Medicine, Case Western Reserve University, Cleveland, OH 44195, USA
| | - Marilyn Seyfi
- Genomic Medicine Institute, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
| | - Feixiong Cheng
- Genomic Medicine Institute, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA; Cleveland Clinic Lerner College of Medicine, Case Western Reserve University, Cleveland, OH 44195, USA; Case Comprehensive Cancer Center, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Charis Eng
- Genomic Medicine Institute, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA; Cleveland Clinic Lerner College of Medicine, Case Western Reserve University, Cleveland, OH 44195, USA; Case Comprehensive Cancer Center, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH 44195, USA; Department of Genetics and Genome Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
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12
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Abstract
Even after a century of investigation, our understanding of how enzymes work remains far from complete. In particular, several factors that enable enzymes to achieve high catalytic efficiencies remain only poorly understood. A number of theories have been developed, which propose or reaffirm that enzymes work as structural scaffolds, serving to bring together and properly orient the participants so that the reaction can proceed; therefore, leading to enzymes being viewed as only passive participants in the catalyzed reaction. A growing body of evidence shows that enzymes are not rigid structures but are constantly undergoing a wide range of internal motions and conformational fluctuations. In this Perspective, on the basis of studies from our group, we discuss the emerging biophysical model of enzyme catalysis that provides a detailed understanding of the interconnection among internal protein motions, conformational substates, enzyme mechanisms, and the catalytic efficiency of enzymes. For a number of enzymes, networks of conserved residues that extend from the surface of the enzyme all the way to the active site have been discovered. These networks are hypothesized to serve as pathways of energy transfer that enables thermodynamical coupling of the surrounding solvent with enzyme catalysis and play a role in promoting enzyme function. Additionally, the role of enzyme structure and electrostatic effects has been well acknowledged for quite some time. Collectively, the recent knowledge gained about enzyme mechanisms suggests that the conventional paradigm of enzyme structure encoding function is incomplete and needs to be extended to structure encodes dynamics, and together these enzyme features encode function including catalytic rate acceleration.
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Affiliation(s)
- Pratul K Agarwal
- Department of Biochemistry & Cellular and Molecular Biology , University of Tennessee , Knoxville , Tennessee 37996 , United States
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13
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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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14
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Modulation of allosteric coupling by mutations: from protein dynamics and packing to altered native ensembles and function. Curr Opin Struct Biol 2018; 54:1-9. [PMID: 30268910 PMCID: PMC6420056 DOI: 10.1016/j.sbi.2018.09.004] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 08/13/2018] [Accepted: 09/10/2018] [Indexed: 01/12/2023]
Abstract
A large body of work has gone into understanding the effect of mutations on protein structure and function. Conventional treatments have involved quantifying the change in stability, activity and relaxation rates of the mutants with respect to the wild-type protein. However, it is now becoming increasingly apparent that mutational perturbations consistently modulate the packing and dynamics of a significant fraction of protein residues, even those that are located >10–15 Å from the mutated site. Such long-range modulation of protein features can distinctly tune protein stability and the native conformational ensemble contributing to allosteric modulation of function. In this review, I summarize a series of experimental and computational observations that highlight the incredibly pliable nature of proteins and their response to mutational perturbations manifested via the intra-protein interaction network. I highlight how an intimate understanding of mutational effects could pave the way for integrating stability, folding, cooperativity and even allostery within a single physical framework.
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15
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Mhashal AR, Pshetitsky Y, Eitan R, Cheatum CM, Kohen A, Major DT. Effect of Asp122 Mutation on the Hydride Transfer in E. coli DHFR Demonstrates the Goldilocks of Enzyme Flexibility. J Phys Chem B 2018; 122:8006-8017. [PMID: 30040418 DOI: 10.1021/acs.jpcb.8b05556] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Dihydrofolate reductase (DHFR) catalyzes the reduction of dihydrofolate (DHF) to tetrahydrofolate (THF) in the presence of NADPH. The key hydride transfer step in the reaction is facilitated by a combination of enzyme active site preorganization and correlated protein motions in the Michaelis-Menten (E:NADPH:DHF) complex. The present theoretical study employs mutagenesis to examine the relation between structural and functional properties of the enzyme. We mutate Asp122 in Escherichia coli DHFR, which is a conserved amino acid in the DHFR family. The consequent effect of the mutation on enzyme catalysis is examined from an energetic, structural and short-time dynamic perspective. Our investigations suggest that the structural and short-time dynamic perturbations caused by Asp122X mutations (X = Asn, Ser, Ala) are along the reaction coordinate and lower the rate of hydride transfer. Importantly, analysis of the correlated and principle component motions in the enzyme suggest that the mutation alters the coupled motions that are present in the wild-type enzyme. In the case of D122N and D122S, the mutations inhibit coupled motion, whereas in the case of D122A, the mutation enhances coupled motion, although all mutations result in similar rate reduction. These results emphasize a Goldilocks principle of enzyme flexibility, that is, enzymes should neither be too rigid nor too flexible.
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Affiliation(s)
- Anil R Mhashal
- Department of Chemistry and the Lise Meitner-Minerva Center of Computational Quantum Chemistry , Bar-Ilan University , Ramat-Gan 52900 , Israel
| | - Yaron Pshetitsky
- Department of Chemistry and the Lise Meitner-Minerva Center of Computational Quantum Chemistry , Bar-Ilan University , Ramat-Gan 52900 , Israel
| | - Reuven Eitan
- Department of Chemistry and the Lise Meitner-Minerva Center of Computational Quantum Chemistry , Bar-Ilan University , Ramat-Gan 52900 , Israel
| | - Christopher M Cheatum
- Department of Chemistry , University of Iowa , Iowa City , Iowa 52242 , United States
| | - Amnon Kohen
- Department of Chemistry , University of Iowa , Iowa City , Iowa 52242 , United States
| | - Dan Thomas Major
- Department of Chemistry and the Lise Meitner-Minerva Center of Computational Quantum Chemistry , Bar-Ilan University , Ramat-Gan 52900 , Israel
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16
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Shanmuganatham KK, Wallace RS, Ting-I Lee A, Plapp BV. Contribution of buried distal amino acid residues in horse liver alcohol dehydrogenase to structure and catalysis. Protein Sci 2018; 27:750-768. [PMID: 29271062 DOI: 10.1002/pro.3370] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Revised: 12/18/2017] [Accepted: 12/20/2017] [Indexed: 01/06/2023]
Abstract
The dynamics of enzyme catalysis range from the slow time scale (∼ms) for substrate binding and conformational changes to the fast time (∼ps) scale for reorganization of substrates in the chemical step. The contribution of global dynamics to catalysis by alcohol dehydrogenase was tested by substituting five different, conserved amino acid residues that are distal from the active site and located in the hinge region for the conformational change or in hydrophobic clusters. X-ray crystallography shows that the structures for the G173A, V197I, I220 (V, L, or F), V222I, and F322L enzymes complexed with NAD+ and an analogue of benzyl alcohol are almost identical, except for small perturbations at the sites of substitution. The enzymes have very similar kinetic constants for the oxidation of benzyl alcohol and reduction of benzaldehyde as compared to the wild-type enzyme, and the rates of conformational changes are not altered. Less conservative substitutions of these amino acid residues, such as G173(V, E, K, or R), V197(G, S, or T), I220(G, S, T, or N), and V222(G, S, or T) produced unstable or poorly expressed proteins, indicating that the residues are critical for global stability. The enzyme scaffold accommodates conservative substitutions of distal residues, and there is no evidence that fast, global dynamics significantly affect the rate constants for hydride transfers. In contrast, other studies show that proximal residues significantly participate in catalysis.
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Affiliation(s)
- Karthik K Shanmuganatham
- Department of Biochemistry, The University of Iowa, Iowa City, IA, 52242-1109.,Diagnostic Virology Laboratory, USDA, Ames, IA, 50010
| | - Rachel S Wallace
- Department of Biochemistry, The University of Iowa, Iowa City, IA, 52242-1109.,Department of Physiology, School of Biomedical Sciences, University of Otago, Dunedin, 9054, New Zealand
| | - Ann Ting-I Lee
- Department of Biochemistry, The University of Iowa, Iowa City, IA, 52242-1109.,No 92, Jing Mao 1st Rd., Taichung, Taiwan, 406, Republic of China
| | - Bryce V Plapp
- Department of Biochemistry, The University of Iowa, Iowa City, IA, 52242-1109
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17
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Świderek K, Arafet K, Kohen A, Moliner V. Benchmarking Quantum Mechanics/Molecular Mechanics (QM/MM) Methods on the Thymidylate Synthase-Catalyzed Hydride Transfer. J Chem Theory Comput 2017; 13:1375-1388. [PMID: 28192669 PMCID: PMC5371049 DOI: 10.1021/acs.jctc.6b01032] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Given the ubiquity of hydride-transfer reactions in enzyme-catalyzed processes, identifying the appropriate computational method for evaluating such biological reactions is crucial to perform theoretical studies of these processes. In this paper, the hydride-transfer step catalyzed by thymidylate synthase (TSase) is studied by examining hybrid quantum mechanics/molecular mechanics (QM/MM) potentials via multiple semiempirical methods and the M06-2X hybrid density functional. Calculations of protium and tritium transfer in these reactions across a range of temperatures allowed calculation of the temperature dependence of kinetic isotope effects (KIE). Dynamics and quantum-tunneling effects are revealed to have little effect on the reaction rate, but are significant in determining the KIEs and their temperature dependence. A good agreement with experiments is found, especially when computed for RM1/MM simulations. The small temperature dependence of quantum tunneling corrections and the quasiclassical contribution term cancel each other, while the recrossing transmission coefficient seems to be temperature-independent over the interval of 5-40 °C.
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Affiliation(s)
- Katarzyna Świderek
- Departament de Química Física i Analítica, Universitat Jaume I , 12071 Castelló, Spain
- Institute of Applied Radiation Chemistry, Lodz University of Technology , 90-924 Lodz, Poland
| | - Kemel Arafet
- Departament de Química Física i Analítica, Universitat Jaume I , 12071 Castelló, Spain
| | - Amnon Kohen
- Department of Chemistry, University of Iowa , Iowa City, Iowa 52242, United States
| | - Vicent Moliner
- Departament de Química Física i Analítica, Universitat Jaume I , 12071 Castelló, Spain
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18
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Luk LYP, Loveridge EJ, Allemann RK. Protein motions and dynamic effects in enzyme catalysis. Phys Chem Chem Phys 2016; 17:30817-27. [PMID: 25854702 DOI: 10.1039/c5cp00794a] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The role of protein motions in promoting the chemical step of enzyme catalysed reactions remains a subject of considerable debate. Here, a unified view of the role of protein dynamics in dihydrofolate reductase catalysis is described. Recently the role of such motions has been investigated by characterising the biophysical properties of isotopically substituted enzymes through a combination of experimental and computational analyses. Together with previous work, these results suggest that dynamic coupling to the chemical coordinate is detrimental to catalysis and may have been selected against during DHFR evolution. The full catalytic power of Nature's catalysts appears to depend on finely tuning protein motions in each step of the catalytic cycle.
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Affiliation(s)
- Louis Y P Luk
- School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT, UK.
| | - E Joel Loveridge
- School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT, UK.
| | - Rudolf K Allemann
- School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT, UK.
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19
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Abstract
Advances in computational and experimental methods in enzymology have aided comprehension of enzyme-catalyzed chemical reactions. The main difficulty in comparing computational findings to rate measurements is that the first examines a single energy barrier, while the second frequently reflects a combination of many microscopic barriers. We present here intrinsic kinetic isotope effects and their temperature dependence as a useful experimental probe of a single chemical step in a complex kinetic cascade. Computational predictions are tested by this method for two model enzymes: dihydrofolate reductase and thymidylate synthase. The description highlights the significance of collaboration between experimentalists and theoreticians to develop a better understanding of enzyme-catalyzed chemical conversions.
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Affiliation(s)
- P Singh
- University of Iowa, Iowa City, IA, United States
| | - Z Islam
- University of Iowa, Iowa City, IA, United States
| | - A Kohen
- University of Iowa, Iowa City, IA, United States.
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20
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Gagné D, French RL, Narayanan C, Simonović M, Agarwal PK, Doucet N. Perturbation of the Conformational Dynamics of an Active-Site Loop Alters Enzyme Activity. Structure 2015; 23:2256-2266. [PMID: 26655472 DOI: 10.1016/j.str.2015.10.011] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Revised: 10/05/2015] [Accepted: 10/13/2015] [Indexed: 01/28/2023]
Abstract
The role of internal dynamics in enzyme function is highly debated. Specifically, how small changes in structure far away from the reaction site alter protein dynamics and overall enzyme mechanisms is of wide interest in protein engineering. Using RNase A as a model, we demonstrate that elimination of a single methyl group located >10 Å away from the reaction site significantly alters conformational integrity and binding properties of the enzyme. This A109G mutation does not perturb structure or thermodynamic stability, both in the apo and ligand-bound states. However, significant enhancement in conformational dynamics was observed for the bound variant, as probed over nano- to millisecond timescales, resulting in major ligand repositioning. These results illustrate the large effects caused by small changes in structure on long-range conformational dynamics and ligand specificities within proteins, further supporting the importance of preserving wild-type dynamics in enzyme systems that rely on flexibility for function.
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Affiliation(s)
- Donald Gagné
- INRS-Institut Armand-Frappier, Université du Québec, 531 Boulevard des Prairies, Laval, QC H7V 1B7, Canada
| | - Rachel L French
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 900 South Ashland, Chicago, IL 60607, USA
| | - Chitra Narayanan
- INRS-Institut Armand-Frappier, Université du Québec, 531 Boulevard des Prairies, Laval, QC H7V 1B7, Canada
| | - Miljan Simonović
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 900 South Ashland, Chicago, IL 60607, USA
| | - Pratul K Agarwal
- Computational Biology Institute and Computer Science and Mathematics Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37830, USA; Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
| | - Nicolas Doucet
- INRS-Institut Armand-Frappier, Université du Québec, 531 Boulevard des Prairies, Laval, QC H7V 1B7, Canada; PROTEO, the Québec Network for Research on Protein Function, Engineering, and Applications, 1045 Avenue de la Médecine, Université Laval, QC G1V 0A6, Canada; GRASP, the Groupe de Recherche Axé sur la Structure des Protéines, 3649 Promenade Sir William Osler, McGill University, Montréal, QC H3G 0B1, Canada.
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21
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Luk LYP, Ruiz-Pernía JJ, Adesina AS, Loveridge EJ, Tuñón I, Moliner V, Allemann RK. Chemical Ligation and Isotope Labeling to Locate Dynamic Effects during Catalysis by Dihydrofolate Reductase. Angew Chem Int Ed Engl 2015; 54:9016-20. [PMID: 26079622 PMCID: PMC4985705 DOI: 10.1002/anie.201503968] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Indexed: 11/21/2022]
Abstract
Chemical ligation has been used to alter motions in specific regions of dihydrofolate reductase from E. coli and to investigate the effects of localized motional changes on enzyme catalysis. Two isotopic hybrids were prepared; one with the mobile N-terminal segment containing heavy isotopes ((2) H, (13) C, (15) N) and the remainder of the protein with natural isotopic abundance, and the other one with only the C-terminal segment isotopically labeled. Kinetic investigations indicated that isotopic substitution of the N-terminal segment affected only a physical step of catalysis, whereas the enzyme chemistry was affected by protein motions from the C-terminal segment. QM/MM studies support the idea that dynamic effects on catalysis mostly originate from the C-terminal segment. The use of isotope hybrids provides insights into the microscopic mechanism of dynamic coupling, which is difficult to obtain with other studies, and helps define the dynamic networks of intramolecular interactions central to enzyme catalysis.
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Affiliation(s)
- Louis Y P Luk
- School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT (UK)
| | - J Javier Ruiz-Pernía
- Departament de Química Física i Analítica, Universitat Jaume I, 12071 Castelló (Spain)
| | | | - E Joel Loveridge
- School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT (UK)
| | - Iñaki Tuñón
- Departament de Química Física, Universitat de València, 46100 Burjassot (Spain).
| | - Vincent Moliner
- Departament de Química Física i Analítica, Universitat Jaume I, 12071 Castelló (Spain).
| | - Rudolf K Allemann
- School of Chemistry, Cardiff University, Park Place, Cardiff, CF10 3AT (UK).
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22
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Luk LYP, Ruiz-Pernía JJ, Adesina AS, Loveridge EJ, Tuñón I, Moliner V, Allemann RK. Chemical Ligation and Isotope Labeling to Locate Dynamic Effects during Catalysis by Dihydrofolate Reductase. Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201503968] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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23
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Singh P, Francis K, Kohen A. Network of remote and local protein dynamics in dihydrofolate reductase catalysis. ACS Catal 2015; 5:3067-3073. [PMID: 27182453 DOI: 10.1021/acscatal.5b00331] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Molecular dynamics calculations and bionformatic studies of dihydrofolate reductase (DHFR) have suggested a network of coupled motions across the whole protein that is correlated to the reaction coordinate. Experimental studies demonstrated that distal residues G121, M42 and F125 in E. coli DHFR participate in that network. The missing link in our understanding of DHFR catalysis is the lack of a mechanism by which such remote residues can affect the catalyzed chemistry at the active site. Here, we present a study of the temperature dependence of intrinsic kinetic isotope effects (KIEs) that indicates synergism between a remote residue in that dynamic network, G121, and the active site's residue I14. The intrinsic KIEs for the I14A-G121V double mutant showed steeper temperature dependence (ΔEa(T-H)) than expected from comparison of the wild type and two single mutants. That effect was non-additive, i.e., ΔEa(T-H)G121V +ΔEa(T-H) I14A < ΔEa(T-H) double mutant, which indicates a synergism between the two residues. This finding links the remote residues in the network under investigation to the enzyme's active site, providing a mechanism by which these residues can be coupled to the catalyzed chemistry. This experimental evidence validates calculations proposing that both remote and active site residues constitute a network of coupled promoting motions correlated to the bond activation step (C-H→C hydride transfer in this case). Additionally, the effect of I14A and G121V mutations on single turnover rates was additive rather than synergistic. Although single turnover rate measurements are more readily available and thus more popular than assessing intrinsic kinetic isotope effects, the current finding demonstrates that for these rates, which in DHFR reflect several microscopic rate constants, can fall short of revealing the nature of the C-H bond activation per se.
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Affiliation(s)
- Priyanka Singh
- The Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242, United States
| | - Kevin Francis
- The Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242, United States
| | - Amnon Kohen
- The Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242, United States
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24
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Meghdari M, Gao N, Abdullahi A, Stokes E, Calhoun DH. Carboxyl-terminal truncations alter the activity of the human α-galactosidase A. PLoS One 2015; 10:e0118341. [PMID: 25719393 PMCID: PMC4342250 DOI: 10.1371/journal.pone.0118341] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 01/13/2015] [Indexed: 12/17/2022] Open
Abstract
Fabry disease is an X-linked inborn error of glycolipid metabolism caused by deficiency of the human lysosomal enzyme, α-galactosidase A (αGal), leading to strokes, myocardial infarctions, and terminal renal failure, often leading to death in the fourth or fifth decade of life. The enzyme is responsible for the hydrolysis of terminal α-galactoside linkages in various glycolipids. Enzyme replacement therapy (ERT) has been approved for the treatment of Fabry disease, but adverse reactions, including immune reactions, make it desirable to generate improved methods for ERT. One approach to circumvent these adverse reactions is the development of derivatives of the enzyme with more activity per mg. It was previously reported that carboxyl-terminal deletions of 2 to 10 amino acids led to increased activity of about 2 to 6-fold. However, this data was qualitative or semi-quantitative and relied on comparison of the amounts of mRNA present in Northern blots with αGal enzyme activity using a transient expression system in COS-1 cells. Here we follow up on this report by constructing and purifying mutant enzymes with deletions of 2, 4, 6, 8, and 10 C-terminal amino acids (Δ2, Δ4, Δ6, Δ8, Δ10) for unambiguous quantitative enzyme assays. The results reported here show that the kcat/Km approximately doubles with deletions of 2, 4, 6 and 10 amino acids (0.8 to 1.7-fold effect) while a deletion of 8 amino acids decreases the kcat/Km (7.2-fold effect). These results indicate that the mutated enzymes with increased activity constructed here would be expected to have a greater therapeutic effect on a per mg basis, and could therefore reduce the likelihood of adverse infusion related reactions in Fabry patients receiving ERT treatment. These results also illustrate the principle that in vitro mutagenesis can be used to generate αGal derivatives with improved enzyme activity.
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Affiliation(s)
- Mariam Meghdari
- Chemistry Dept., City College of New York, New York, NY, USA
| | - Nicholas Gao
- Chemistry Dept., City College of New York, New York, NY, USA
| | - Abass Abdullahi
- Biology & Medical Lab Technology, Bronx Community College, Bronx, NY, USA
| | - Erin Stokes
- Chemistry Dept., City College of New York, New York, NY, USA
| | - David H. Calhoun
- Chemistry Dept., City College of New York, New York, NY, USA
- * E-mail:
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25
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Singh P, Abeysinghe T, Kohen A. Linking protein motion to enzyme catalysis. Molecules 2015; 20:1192-209. [PMID: 25591120 PMCID: PMC4341894 DOI: 10.3390/molecules20011192] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2014] [Accepted: 01/07/2015] [Indexed: 12/01/2022] Open
Abstract
Enzyme motions on a broad range of time scales can play an important role in various intra- and intermolecular events, including substrate binding, catalysis of the chemical conversion, and product release. The relationship between protein motions and catalytic activity is of contemporary interest in enzymology. To understand the factors influencing the rates of enzyme-catalyzed reactions, the dynamics of the protein-solvent-ligand complex must be considered. The current review presents two case studies of enzymes—dihydrofolate reductase (DHFR) and thymidylate synthase (TSase)—and discusses the role of protein motions in their catalyzed reactions. Specifically, we will discuss the utility of kinetic isotope effects (KIEs) and their temperature dependence as tools in probing such phenomena.
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Affiliation(s)
- Priyanka Singh
- Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA.
| | - Thelma Abeysinghe
- Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA.
| | - Amnon Kohen
- Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA.
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26
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Luk LP, Loveridge EJ, Allemann RK. Different dynamical effects in mesophilic and hyperthermophilic dihydrofolate reductases. J Am Chem Soc 2014; 136:6862-5. [PMID: 24779446 PMCID: PMC4046772 DOI: 10.1021/ja502673h] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2014] [Indexed: 01/18/2023]
Abstract
The role of protein dynamics in the reaction catalyzed by dihydrofolate reductase from the hyperthermophile Thermotoga maritima (TmDHFR) has been examined by enzyme isotope substitution ((15)N, (13)C, (2)H). In contrast to all other enzyme reactions investigated previously, including DHFR from Escherichia coli (EcDHFR), for which isotopic substitution led to decreased reactivity, the rate constant for the hydride transfer step is not affected by isotopic substitution of TmDHFR. TmDHFR therefore appears to lack the coupling of protein motions to the reaction coordinate that have been identified for EcDHFR catalysis. Clearly, dynamical coupling is not a universal phenomenon that affects the efficiency of enzyme catalysis.
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Affiliation(s)
- Louis
Y. P. Luk
- School
of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
| | - E. Joel Loveridge
- School
of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
| | - Rudolf K. Allemann
- School
of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
- Cardiff
Catalysis Institute, School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
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27
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Doron D, Kohen A, Nam K, Major DT. How Accurate Are Transition States from Simulations of Enzymatic Reactions? J Chem Theory Comput 2014; 10:1863-1871. [PMID: 24860275 PMCID: PMC4025581 DOI: 10.1021/ct5000742] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Indexed: 11/30/2022]
Abstract
The rate expression of traditional transition state theory (TST) assumes no recrossing of the transition state (TS) and thermal quasi-equilibrium between the ground state and the TS. Currently, it is not well understood to what extent these assumptions influence the nature of the activated complex obtained in traditional TST-based simulations of processes in the condensed phase in general and in enzymes in particular. Here we scrutinize these assumptions by characterizing the TSs for hydride transfer catalyzed by the enzyme Escherichia coli dihydrofolate reductase obtained using various simulation approaches. Specifically, we compare the TSs obtained with common TST-based methods and a dynamics-based method. Using a recently developed accurate hybrid quantum mechanics/molecular mechanics potential, we find that the TST-based and dynamics-based methods give considerably different TS ensembles. This discrepancy, which could be due equilibrium solvation effects and the nature of the reaction coordinate employed and its motion, raises major questions about how to interpret the TSs determined by common simulation methods. We conclude that further investigation is needed to characterize the impact of various TST assumptions on the TS phase-space ensemble and on the reaction kinetics.
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Affiliation(s)
- Dvir Doron
- Department
of Chemistry and the Lise Meitner-Minerva Center of Computational
Quantum Chemistry, Bar-Ilan University, Ramat-Gan 5290002, Israel
| | - Amnon Kohen
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Kwangho Nam
- Department
of Chemistry and Computational Life Science Cluster (CLiC), Umeå University, 901 87 Umeå, Sweden
| | - Dan Thomas Major
- Department
of Chemistry and the Lise Meitner-Minerva Center of Computational
Quantum Chemistry, Bar-Ilan University, Ramat-Gan 5290002, Israel
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28
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Swiderek K, Ruiz-Pernía JJ, Moliner V, Tuñón I. Heavy enzymes--experimental and computational insights in enzyme dynamics. Curr Opin Chem Biol 2014; 21:11-8. [PMID: 24709164 DOI: 10.1016/j.cbpa.2014.03.005] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Accepted: 03/14/2014] [Indexed: 11/18/2022]
Abstract
The role of protein motions in the chemical step of enzyme-catalyzed reactions is the subject of an open debate in the scientific literature. The systematic use of isotopically substituted enzymes has been revealed as a useful tool to quantify the role of these motions. According to the Born-Oppenheimer approximation, changing the mass of the protein does not change the forces acting on the system but alters the frequencies of the protein motions, which in turn can affect the rate constant. Experimental and theoretical studies carried out in this field are presented in this article and discussed in the framework of Transition State Theory.
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Affiliation(s)
- Katarzyna Swiderek
- Departamento de Química Física, Universitat de València, 46100 Burjassot, Spain; Institute of Applied Radiation Chemistry, Lodz University of Technology, 90-924 Lodz, Poland
| | - J Javier Ruiz-Pernía
- Departamento de Química Física y Analítica, Universitat Jaume I, 12071 Castellón, Spain
| | - Vicent Moliner
- Departamento de Química Física y Analítica, Universitat Jaume I, 12071 Castellón, Spain.
| | - Iñaki Tuñón
- Departamento de Química Física, Universitat de València, 46100 Burjassot, Spain.
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29
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Micozzi D, Carpi FM, Pucciarelli S, Polzonetti V, Polidori P, Vilar S, Williams B, Costanzi S, Vincenzetti S. Human cytidine deaminase: a biochemical characterization of its naturally occurring variants. Int J Biol Macromol 2014; 63:64-74. [PMID: 24183806 PMCID: PMC3904506 DOI: 10.1016/j.ijbiomac.2013.10.029] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Revised: 10/19/2013] [Accepted: 10/21/2013] [Indexed: 01/10/2023]
Abstract
Human cytidine deaminase is an enzyme of the pyrimidine salvage pathways that metabolizes several cytosine nucleoside analogs used as prodrugs in chemotherapy. We carried out a characterization of the cytidine deaminase 79A>C and 208G>A Single Nucleotide Polymorphisms, in order to highlight their functional role and provide data that could help fine-tune the chemotherapic use of cytosine nucleosides in patients carrying the above mentioned SNPs. The 79A>C SNP results in a K27Q change in a protein region not involved in the catalytic event. The 208G>A SNP produces an alanine to threonine substitution (A70T) within the conserved catalytic domain. Q27 variant is endowed with a greater catalytic efficiency toward the natural substrates and the antileukemic agent cytarabine (Ara-C), when compared to K27 variant. Molecular modeling, protein stability experiments and site-directed mutagenesis suggest that K27 variant may have an increased stability with respect to Q27 due to an ionic interaction between a lysine residue at position 27 and a glutamate residue at position 24. The T70 variant has a lower catalytic efficiency toward the analyzed substrates when compared to the A70 variant, suggesting that patients carrying the 208G>A SNP may have a greater exposure to cytosine based pro drugs, with possible toxicity consequences.
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Affiliation(s)
- Daniela Micozzi
- School of Biosciences and Biotechnology, University of Camerino, via Gentile III da Varano, 62032 Camerino, MC, Italy
| | - Francesco Martino Carpi
- School of Biosciences and Biotechnology, University of Camerino, via Gentile III da Varano, 62032 Camerino, MC, Italy
| | - Stefania Pucciarelli
- School of Biosciences and Biotechnology, University of Camerino, via Gentile III da Varano, 62032 Camerino, MC, Italy
| | - Valeria Polzonetti
- School of Biosciences and Biotechnology, University of Camerino, via Gentile III da Varano, 62032 Camerino, MC, Italy
| | - Paolo Polidori
- School of Pharmacy, University of Camerino, via circonvallazione 93/95, 62024 Matelica, MC, Italy
| | - Santiago Vilar
- Department of Organic Chemistry, Faculty of Pharmacy, University of Santiago de Compostela, Santiago de Compostela 15782, Spain
| | - Brian Williams
- Department of Chemistry, American University, Washington, DC 20016, USA
| | - Stefano Costanzi
- Department of Chemistry, American University, Washington, DC 20016, USA.
| | - Silvia Vincenzetti
- School of Veterinary Medical Sciences, University of Camerino, via circonvallazione 93/95, 62024 Matelica, MC, Italy.
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30
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Singh P, Sen A, Francis K, Kohen A. Extension and limits of the network of coupled motions correlated to hydride transfer in dihydrofolate reductase. J Am Chem Soc 2014; 136:2575-82. [PMID: 24450297 PMCID: PMC3985941 DOI: 10.1021/ja411998h] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Enzyme catalysis
has been studied extensively, but the role of
enzyme dynamics in the catalyzed chemical conversion is still an enigma.
The enzyme dihydrofolate reductase (DHFR) is often used as a model
system to assess a network of coupled motions across the protein that
may affect the catalyzed chemical transformation. Molecular dynamics
simulations, quantum mechanical/molecular mechanical studies, and
bioinformatics studies have suggested the presence of a “global
dynamic network” of residues in DHFR. Earlier studies of two
DHFR distal mutants, G121V and M42W, indicated that these residues
affect the chemical step synergistically. While this finding was in
accordance with the concept of a network of functional motions across
the protein, two residues do not constitute a network. To better define
the extent and limits of the proposed network, the current work studied
two remote residues predicted to be part of the same network: W133
and F125. The effect of mutations in these residues on the nature
of the chemical step was examined via measurements of the temperature-dependence
of the intrinsic kinetic isotope effects (KIEs) and other kinetic
parameters, and double mutants were used to tie the findings to G121
and M42. The findings indicate that residue F125, which was implicated
by both calculations and bioinformatic methods, is a part of the same
global dynamic network as G121 and M42, while W133, implicated only
by bioinformatics, is not. These findings extend our understanding
of the proposed network and the relations between functional and genomic
couplings. Delineating that network illuminates the need to consider
remote residues and protein structural dynamics in the rational design
of drugs and of biomimetic catalysts.
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Affiliation(s)
- Priyanka Singh
- Department of Chemistry, The University of Iowa , Iowa City, Iowa 52242, United States
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31
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Ruiz-Pernia JJ, Luk LYP, García-Meseguer R, Martí S, Loveridge EJ, Tuñón I, Moliner V, Allemann RK. Increased dynamic effects in a catalytically compromised variant of Escherichia coli dihydrofolate reductase. J Am Chem Soc 2013; 135:18689-96. [PMID: 24252106 PMCID: PMC3949409 DOI: 10.1021/ja410519h] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Indexed: 01/19/2023]
Abstract
Isotopic substitution ((15)N, (13)C, (2)H) of a catalytically compromised variant of Escherichia coli dihydrofolate reductase, EcDHFR-N23PP/S148A, has been used to investigate the effect of these mutations on catalysis. The reduction of the rate constant of the chemical step in the EcDHFR-N23PP/S148A catalyzed reaction is essentially a consequence of an increase of the quasi-classical free energy barrier and to a minor extent of an increased number of recrossing trajectories on the transition state dividing surface. Since the variant enzyme is less well set up to catalyze the reaction, a higher degree of active site reorganization is needed to reach the TS. Although millisecond active site motions are lost in the variant, there is greater flexibility on the femtosecond time scale. The "dynamic knockout" EcDHFR-N23PP/S148A is therefore a "dynamic knock-in" at the level of the chemical step, and the increased dynamic coupling to the chemical coordinate is in fact detrimental to catalysis. This finding is most likely applicable not just to hydrogen transfer in EcDHFR but also to other enzymatic systems.
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Affiliation(s)
- J. Javier Ruiz-Pernia
- Departament
de Química Física i Analítica, Universitat Jaume I, 12071 Castello, Spain
| | - Louis Y. P. Luk
- School
of Chemistry & Cardiff Catalysis Institute, Cardiff University, Park Place, Cardiff, CF10
3AT, U.K.
| | | | - Sergio Martí
- Departament
de Química Física i Analítica, Universitat Jaume I, 12071 Castello, Spain
| | - E. Joel Loveridge
- School
of Chemistry & Cardiff Catalysis Institute, Cardiff University, Park Place, Cardiff, CF10
3AT, U.K.
| | - Iñaki Tuñón
- Departament
de Química Física, Universitat
de València, 46100 Burjassot, Spain
| | - Vicent Moliner
- Departament
de Química Física i Analítica, Universitat Jaume I, 12071 Castello, Spain
| | - Rudolf K. Allemann
- School
of Chemistry & Cardiff Catalysis Institute, Cardiff University, Park Place, Cardiff, CF10
3AT, U.K.
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32
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Solvent environments significantly affect the enzymatic function of Escherichia coli dihydrofolate reductase: comparison of wild-type protein and active-site mutant D27E. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2013; 1834:2782-94. [PMID: 24140567 DOI: 10.1016/j.bbapap.2013.09.024] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2013] [Revised: 09/17/2013] [Accepted: 09/30/2013] [Indexed: 11/23/2022]
Abstract
To investigate the contribution of solvent environments to the enzymatic function of Escherichia coli dihydrofolate reductase (DHFR), the salt-, pH-, and pressure-dependence of the enzymatic function of the wild-type protein were compared with those of the active-site mutant D27E in relation to their structure and stability. The salt concentration-dependence of enzymatic activity indicated that inorganic cations bound to and inhibited the activity of wild-type DHFR at neutral pH. The BaCl2 concentration-dependence of the (1)H-(15)N HSQC spectra of the wild-type DHFR-folate binary complex showed that the cation-binding site was located adjacent to the Met20 loop. The insensitivity of the D27E mutant to univalent cations, the decreased optimal pH for its enzymatic activity, and the increased Km and Kd values for its substrate dihydrofolate suggested that the substrate-binding cleft of the mutant was slightly opened to expose the active-site side chain to the solvent. The marginally increased fluorescence intensity and decreased volume change due to unfolding of the mutant also supported this structural change or the modified cavity and hydration. Surprisingly, the enzymatic activity of the mutant increased with pressurization up to 250MPa together with negative activation volumes of -4.0 or -4.8mL/mol, depending on the solvent system, while that of the wild-type was decreased and had positive activation volumes of 6.1 or 7.7mL/mol. These results clearly indicate that the insertion of a single methylene at the active site could substantially change the enzymatic reaction mechanism of DHFR, and solvent environments play important roles in the function of this enzyme.
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33
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Unraveling the role of protein dynamics in dihydrofolate reductase catalysis. Proc Natl Acad Sci U S A 2013; 110:16344-9. [PMID: 24065822 DOI: 10.1073/pnas.1312437110] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protein dynamics have controversially been proposed to be at the heart of enzyme catalysis, but identification and analysis of dynamical effects in enzyme-catalyzed reactions have proved very challenging. Here, we tackle this question by comparing an enzyme with its heavy ((15)N, (13)C, (2)H substituted) counterpart, providing a subtle probe of dynamics. The crucial hydride transfer step of the reaction (the chemical step) occurs more slowly in the heavy enzyme. A combination of experimental results, quantum mechanics/molecular mechanics simulations, and theoretical analyses identify the origins of the observed differences in reactivity. The generally slightly slower reaction in the heavy enzyme reflects differences in environmental coupling to the hydride transfer step. Importantly, the barrier and contribution of quantum tunneling are not affected, indicating no significant role for "promoting motions" in driving tunneling or modulating the barrier. The chemical step is slower in the heavy enzyme because protein motions coupled to the reaction coordinate are slower. The fact that the heavy enzyme is only slightly less active than its light counterpart shows that protein dynamics have a small, but measurable, effect on the chemical reaction rate.
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34
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Boehr DD, Schnell JR, McElheny D, Bae SH, Duggan BM, Benkovic SJ, Dyson HJ, Wright PE. A distal mutation perturbs dynamic amino acid networks in dihydrofolate reductase. Biochemistry 2013; 52:4605-19. [PMID: 23758161 DOI: 10.1021/bi400563c] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Correlated networks of amino acids have been proposed to play a fundamental role in allostery and enzyme catalysis. These networks of amino acids can be traced from surface-exposed residues all the way into the active site, and disruption of these networks can decrease enzyme activity. Substitution of the distal Gly121 residue in Escherichia coli dihydrofolate reductase results in an up to 200-fold decrease in the hydride transfer rate despite the fact that the residue is located 15 Å from the active-site center. In this study, nuclear magnetic resonance relaxation experiments are used to demonstrate that dynamics on the picosecond to nanosecond and microsecond to millisecond time scales are changed significantly in the G121V mutant of dihydrofolate reductase. In particular, picosecond to nanosecond time scale dynamics are decreased in the FG loop (containing the mutated residue at position 121) and the neighboring active-site loop (the Met20 loop) in the mutant compared to those of the wild-type enzyme, suggesting that these loops are dynamically coupled. Changes in methyl order parameters reveal a pathway by which dynamic perturbations can be propagated more than 25 Å across the protein from the site of mutation. All of the enzyme complexes, including the model Michaelis complex with folate and nicotinamide adenine dinucleotide phosphate bound, assume an occluded ground-state conformation, and we do not observe sampling of a higher-energy closed conformation by (15)N R2 relaxation dispersion experiments. This is highly significant, because it is only in the closed conformation that the cofactor and substrate reactive centers are positioned for reaction. The mutation also impairs microsecond to millisecond time scale fluctuations that have been implicated in the release of product from the wild-type enzyme. Our results are consistent with an important role for Gly121 in controlling protein dynamics critical for enzyme function and further validate the dynamic energy landscape hypothesis of enzyme catalysis.
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Affiliation(s)
- David D Boehr
- Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Jason R Schnell
- Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Dan McElheny
- Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Sung-Hun Bae
- Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Brendan M Duggan
- Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Stephen J Benkovic
- The Pennsylvania State University, Department of Chemistry, 414 Wartik Laboratory, University Park, PA 16802, USA
| | - H Jane Dyson
- Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
| | - Peter E Wright
- Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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35
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Abstract
The relationship between protein dynamics and function is a subject of considerable contemporary interest. Although protein motions are frequently observed during ligand binding and release steps, the contribution of protein motions to the catalysis of bond making/breaking processes is more difficult to probe and verify. Here, we show how the quantum mechanical hydrogen tunneling associated with enzymatic C-H bond cleavage provides a unique window into the necessity of protein dynamics for achieving optimal catalysis. Experimental findings support a hierarchy of thermodynamically equilibrated motions that control the H-donor and -acceptor distance and active-site electrostatics, creating an ensemble of conformations suitable for H-tunneling. A possible extension of this view to methyl transfer and other catalyzed reactions is also presented. The impact of understanding these dynamics on the conceptual framework for enzyme activity, inhibitor/drug design, and biomimetic catalyst design is likely to be substantial.
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Affiliation(s)
- Judith P. Klinman
- Department of Chemistry, Department of Molecular and Cell Biology, and the California Institute for Quantitative Sciences, University of California, Berkeley, California 94720;
| | - Amnon Kohen
- Department of Chemistry, University of Iowa, Iowa City, Iowa 52242-1294;
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36
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Cheatum CM, Kohen A. Relationship of femtosecond-picosecond dynamics to enzyme-catalyzed H-transfer. Top Curr Chem (Cham) 2013; 337:1-39. [PMID: 23539379 PMCID: PMC4699684 DOI: 10.1007/128_2012_407] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
At physiological temperatures, enzymes exhibit a broad spectrum of conformations, which interchange via thermally activated dynamics. These conformations are sampled differently in different complexes of the protein and its ligands, and the dynamics of exchange between these conformers depends on the mass of the group that is moving and the length scale of the motion, as well as restrictions imposed by the globular fold of the enzymatic complex. Many of these motions have been examined and their role in the enzyme function illuminated, yet most experimental tools applied so far have identified dynamics at time scales of seconds to nanoseconds, which are much slower than the time scale for H-transfer between two heavy atoms. This chemical conversion and other processes involving cleavage of covalent bonds occur on picosecond to femtosecond time scales, where slower processes mask both the kinetics and dynamics. Here we present a combination of kinetic and spectroscopic methods that may enable closer examination of the relationship between enzymatic C-H → C transfer and the dynamics of the active site environment at the chemically relevant time scale. These methods include kinetic isotope effects and their temperature dependence, which are used to study the kinetic nature of the H-transfer, and 2D IR spectroscopy, which is used to study the dynamics of transition-state- and ground-state-analog complexes. The combination of these tools is likely to provide a new approach to examine the protein dynamics that directly influence the chemical conversion catalyzed by enzymes.
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37
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Tokuriki N, Jackson CJ, Afriat-Jurnou L, Wyganowski KT, Tang R, Tawfik DS. Diminishing returns and tradeoffs constrain the laboratory optimization of an enzyme. Nat Commun 2012; 3:1257. [DOI: 10.1038/ncomms2246] [Citation(s) in RCA: 165] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 11/01/2012] [Indexed: 11/09/2022] Open
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38
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Roston D, Cheatum CM, Kohen A. Hydrogen donor-acceptor fluctuations from kinetic isotope effects: a phenomenological model. Biochemistry 2012; 51:6860-70. [PMID: 22857146 PMCID: PMC3448806 DOI: 10.1021/bi300613e] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Kinetic isotope effects (KIEs) and their temperature dependence can probe the structural and dynamic nature of enzyme-catalyzed proton or hydride transfers. The molecular interpretation of their temperature dependence requires expensive and specialized quantum mechanics/molecular mechanics (QM/MM) calculations to provide a quantitative molecular understanding. Currently available phenomenological models use a nonadiabatic assumption that is not appropriate for most hydride and proton-transfer reactions, while others require more parameters than the experimental data justify. Here we propose a phenomenological interpretation of KIEs based on a simple method to quantitatively link the size and temperature dependence of KIEs to a conformational distribution of the catalyzed reaction. This model assumes adiabatic hydrogen tunneling, and by fitting experimental KIE data, the model yields a population distribution for fluctuations of the distance between donor and acceptor atoms. Fits to data from a variety of proton and hydride transfers catalyzed by enzymes and their mutants, as well as nonenzymatic reactions, reveal that steeply temperature-dependent KIEs indicate the presence of at least two distinct conformational populations, each with different kinetic behaviors. We present the results of these calculations for several published cases and discuss how the predictions of the calculations might be experimentally tested. This analysis does not replace molecular QM/MM investigations, but it provides a fast and accessible way to quantitatively interpret KIEs in the context of a Marcus-like model.
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Affiliation(s)
- Daniel Roston
- Department of Chemistry, University of Iowa, Iowa City, IA 52242
| | | | - Amnon Kohen
- Department of Chemistry, University of Iowa, Iowa City, IA 52242
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39
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Sen A, Stojković V, Kohen A. Synthesis of radiolabeled nicotinamide cofactors from labeled pyridines: versatile probes for enzyme kinetics. Anal Biochem 2012; 430:123-9. [PMID: 22922383 DOI: 10.1016/j.ab.2012.08.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Revised: 08/07/2012] [Accepted: 08/14/2012] [Indexed: 11/30/2022]
Abstract
(14)C-labeled nicotinamide cofactors are widely employed in biomedical investigations, for example, to delineate metabolic pathways, to elucidate enzymatic mechanisms, and as substrates in kinetic isotope effect (KIE) experiments. The (14)C label has generally been located remote from the reactive position, frequently at the adenine ring. Rising costs of commercial precursors and disruptions in the availability of enzymes required for established syntheses have recently made the preparation of labeled nicotinamides such as [Ad-(14)C]NADPH unviable. Here, we report the syntheses and characterization of several alternatives: [carbonyl-(14)C]NADPH, 4R-[carbonyl-(14)C, 4-(2)H]NADPH, and [carbonyl-(14)C, 4-(2)H(2)]NADPH. The new procedures use [carbonyl-(14)C]nicotinamide as starting material, because it is significantly cheaper than other commercial (14)C precursors of NADPH, and require only one commercially available enzyme to prepare NAD(P)(+) and NAD(P)H. The proximity of carbonyl-(14)C to the reactive center raises the risk of an inopportune (14)C isotope effect. This concern has been alleviated via competitive KIE measurements with Escherichia coli dihydrofolate reductase (EcDHFR) that use this specific carbonyl-(14)C NADPH. A combination of binding isotope effect and KIE measurements yielded no significant (12)C/(14)C isotope effect at the amide carbonyl (KIE=1.003±0.004). The reported procedure provides a high-yield, high-purity, and cost-effective alternative to labeled nicotinamide cofactors synthesized by previously published routes.
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Affiliation(s)
- Arundhuti Sen
- Department of Chemistry, University of Iowa, Iowa City, IA 52245, USA
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40
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Weikl TR, Boehr DD. Conformational selection and induced changes along the catalytic cycle of Escherichia coli
dihydrofolate reductase. Proteins 2012; 80:2369-83. [DOI: 10.1002/prot.24123] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Revised: 05/02/2012] [Accepted: 05/09/2012] [Indexed: 01/21/2023]
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41
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Doron D, Kohen A, Major DT. Collective Reaction Coordinate for Hybrid Quantum and Molecular Mechanics Simulations: A Case Study of the Hydride Transfer in Dihydrofolate Reductase. J Chem Theory Comput 2012; 8:2484-96. [PMID: 26588977 DOI: 10.1021/ct300235k] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The optimal description of the reaction coordinate in chemical systems is of great importance in simulating condensed phase reactions. In the current work, we present a collective reaction coordinate which is composed of several geometric coordinates which represent structural progress during the course of a hydride transfer reaction: the antisymmetric reactive stretch coordinate, the donor-acceptor distance (DAD) coordinate, and an orbital rehybridization coordinate. In this approach, the former coordinate serves as a distinguished reaction coordinate, while the latter two serve as environmental, Marcus-type inner-sphere reorganization coordinates. The classical free energy surface is obtained from multidimensional quantum mechanics-molecular mechanics (QM/MM) potential of mean force (PMF) simulations in conjunction with a general and efficient multidimensional weighted histogram method implementation. The minimum free energy path, or the collective reaction coordinate, connecting the dividing hypersurface to reactants and products, is obtained using an iterative scheme. In this approach, the string method is used to find the minimum free energy path. This path guides the multidimensional sampling, while the path is adaptively refined until convergence is achieved. As a model system, we choose the hydride transfer reaction in Escherichia coli dihydrofolate reductase (ecDHFR) using a recently developed accurate semiempirical potential energy surface. To estimate the advantages of the collective reaction coordinate, we perform activated dynamics simulations to obtain the reaction transmission coefficient. The results show that the combination of a distinguished reaction coordinate and an inner-sphere reorganization coordinate considerably reduces the dividing surface recrossing.
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Affiliation(s)
- Dvir Doron
- Department of Chemistry and the Lise Meitner-Minerva Center of Computational Quantum Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Amnon Kohen
- Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Dan Thomas Major
- Department of Chemistry and the Lise Meitner-Minerva Center of Computational Quantum Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel
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42
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Engel H, Doron D, Kohen A, Major DT. Momentum Distribution as a Fingerprint of Quantum Delocalization in Enzymatic Reactions: Open-Chain Path-Integral Simulations of Model Systems and the Hydride Transfer in Dihydrofolate Reductase. J Chem Theory Comput 2012; 8:1223-34. [DOI: 10.1021/ct200874q] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hamutal Engel
- Department of Chemistry and
the Lise Meitner−Minerva Center of Computational Quantum Chemistry,
Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Dvir Doron
- Department of Chemistry and
the Lise Meitner−Minerva Center of Computational Quantum Chemistry,
Bar-Ilan University, Ramat-Gan 52900, Israel
| | - Amnon Kohen
- Department of Chemistry, University
of Iowa, Iowa City, Iowa 52242, United States
| | - Dan Thomas Major
- Department of Chemistry and
the Lise Meitner−Minerva Center of Computational Quantum Chemistry,
Bar-Ilan University, Ramat-Gan 52900, Israel
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43
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Stojković V, Perissinotti LL, Willmer D, Benkovic SJ, Kohen A. Effects of the donor-acceptor distance and dynamics on hydride tunneling in the dihydrofolate reductase catalyzed reaction. J Am Chem Soc 2012; 134:1738-45. [PMID: 22171795 DOI: 10.1021/ja209425w] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A significant contemporary question in enzymology involves the role of protein dynamics and hydrogen tunneling in enhancing enzyme catalyzed reactions. Here, we report a correlation between the donor-acceptor distance (DAD) distribution and intrinsic kinetic isotope effects (KIEs) for the dihydrofolate reductase (DHFR) catalyzed reaction. This study compares the nature of the hydride-transfer step for a series of active-site mutants, where the size of a side chain that modulates the DAD (I14 in E. coli DHFR) is systematically reduced (I14V, I14A, and I14G). The contributions of the DAD and its dynamics to the hydride-transfer step were examined by the temperature dependence of intrinsic KIEs, hydride-transfer rates, activation parameters, and classical molecular dynamics (MD) simulations. Results are interpreted within the framework of the Marcus-like model where the increase in the temperature dependence of KIEs arises as a direct consequence of the deviation of the DAD from its distribution in the wild type enzyme. Classical MD simulations suggest new populations with larger average DADs, as well as broader distributions, and a reduction in the population of the reactive conformers correlated with the decrease in the size of the hydrophobic residue. The more flexible active site in the mutants required more substantial thermally activated motions for effective H-tunneling, consistent with the hypothesis that the role of the hydrophobic side chain of I14 is to restrict the distribution and dynamics of the DAD and thus assist the hydride-transfer. These studies establish relationships between the distribution of DADs, the hydride-transfer rates, and the DAD's rearrangement toward tunneling-ready states. This structure-function correlation shall assist in the interpretation of the temperature dependence of KIEs caused by mutants far from the active site in this and other enzymes, and may apply generally to C-H→C transfer reactions.
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Affiliation(s)
- Vanja Stojković
- Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242, USA
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44
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Baugh L, Le Trong I, Cerutti DS, Mehta N, Gülich S, Stayton PS, Stenkamp RE, Lybrand TP. Second-contact shell mutation diminishes streptavidin-biotin binding affinity through transmitted effects on equilibrium dynamics. Biochemistry 2012; 51:597-607. [PMID: 22145986 DOI: 10.1021/bi201221j] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report a point mutation in the second contact shell of the high-affinity streptavidin-biotin complex that appears to reduce binding affinity through transmitted effects on equilibrium dynamics. The Y54F streptavidin mutation causes a 75-fold loss of binding affinity with 73-fold faster dissociation, a large loss of binding enthalpy (ΔΔH = 3.4 kcal/mol at 37 °C), and a small gain in binding entropy (TΔΔS = 0.7 kcal/mol). The removed Y54 hydroxyl is replaced by a water molecule in the bound structure, but there are no observable changes in structure in the first contact shell and no additional changes surrounding the mutation. Molecular dynamics simulations reveal a large increase in the atomic fluctuation amplitudes for W79, a key biotin contact residue, compared to the fluctuation amplitudes in the wild-type. The increased W79 atomic fluctuation amplitudes are caused by loss of water-mediated hydrogen bonds between the Y54 hydroxyl group and peptide backbone atoms in and near W79. We propose that the increased atomic fluctuation amplitudes diminish the integrity of the W79-biotin interaction and represents a loosening of the "tryptophan collar" that is critical to the slow dissociation and high affinity of streptavidin-biotin binding. These results illustrate how changes in protein dynamics distal to the ligand binding pocket can have a profound impact on ligand binding, even when equilibrium structure is unperturbed.
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Affiliation(s)
- Loren Baugh
- Department of Bioengineering, University of Washington, Seattle, Washington 98195, United States
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Evolutionarily conserved linkage between enzyme fold, flexibility, and catalysis. PLoS Biol 2011; 9:e1001193. [PMID: 22087074 PMCID: PMC3210774 DOI: 10.1371/journal.pbio.1001193] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Accepted: 09/27/2011] [Indexed: 11/19/2022] Open
Abstract
Proteins are intrinsically flexible molecules. The role of internal motions in a protein's designated function is widely debated. The role of protein structure in enzyme catalysis is well established, and conservation of structural features provides vital clues to their role in function. Recently, it has been proposed that the protein function may involve multiple conformations: the observed deviations are not random thermodynamic fluctuations; rather, flexibility may be closely linked to protein function, including enzyme catalysis. We hypothesize that the argument of conservation of important structural features can also be extended to identification of protein flexibility in interconnection with enzyme function. Three classes of enzymes (prolyl-peptidyl isomerase, oxidoreductase, and nuclease) that catalyze diverse chemical reactions have been examined using detailed computational modeling. For each class, the identification and characterization of the internal protein motions coupled to the chemical step in enzyme mechanisms in multiple species show identical enzyme conformational fluctuations. In addition to the active-site residues, motions of protein surface loop regions (>10 Å away) are observed to be identical across species, and networks of conserved interactions/residues connect these highly flexible surface regions to the active-site residues that make direct contact with substrates. More interestingly, examination of reaction-coupled motions in non-homologous enzyme systems (with no structural or sequence similarity) that catalyze the same biochemical reaction shows motions that induce remarkably similar changes in the enzyme–substrate interactions during catalysis. The results indicate that the reaction-coupled flexibility is a conserved aspect of the enzyme molecular architecture. Protein motions in distal areas of homologous and non-homologous enzyme systems mediate similar changes in the active-site enzyme–substrate interactions, thereby impacting the mechanism of catalyzed chemistry. These results have implications for understanding the mechanism of allostery, and for protein engineering and drug design.
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46
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Abstract
We use quantized molecular dynamics simulations to characterize the role of enzyme vibrations in facilitating dihydrofolate reductase hydride transfer. By sampling the full ensemble of reactive trajectories, we are able to quantify and distinguish between statistical and dynamical correlations in the enzyme motion. We demonstrate the existence of nonequilibrium dynamical coupling between protein residues and the hydride tunneling reaction, and we characterize the spatial and temporal extent of these dynamical effects. Unlike statistical correlations, which give rise to nanometer-scale coupling between distal protein residues and the intrinsic reaction, dynamical correlations vanish at distances beyond 4-6 Å from the transferring hydride. This work finds a minimal role for nonlocal vibrational dynamics in enzyme catalysis, and it supports a model in which nanometer-scale protein fluctuations statistically modulate--or gate--the barrier for the intrinsic reaction.
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Brala CJ, Pilepić V, Sajenko I, Karković A, Uršić S. Ions Can Move a Proton-Coupled Electron-Transfer Reaction into Tunneling Regime. Helv Chim Acta 2011. [DOI: 10.1002/hlca.201100035] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Sen A, Yahashiri A, Kohen A. Triple isotopic labeling and kinetic isotope effects: exposing H-transfer steps in enzymatic systems. Biochemistry 2011; 50:6462-8. [PMID: 21688781 DOI: 10.1021/bi2003873] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Kinetic isotope effect (KIE) studies can provide insight into the mechanism and kinetics of specific chemical steps in complex catalytic cascades. Recent results from hydrogen KIE measurements have examined correlations between enzyme dynamics and catalytic function, leading to a surge of studies in this area. Unfortunately, most enzymatic H-transfer reactions are not rate limiting, and the observed KIEs do not reliably reflect the intrinsic KIEs on the chemical step of interest. Given their importance to understanding the chemical step under study, accurate determination of the intrinsic KIE from the observed data is essential. In 1975, Northrop developed an elegant method to assess intrinsic KIEs from their observed values [Northrop, D. B. (1975) Steady-state analysis of kinetic isotope effects in enzymic reactions. Biochemistry 14, 2644-2651]. The Northrop method involves KIE measurements using all three hydrogen isotopes, where one of them serves as the reference isotope. This method has been successfully used with different combinations of observed KIEs over the years, but criteria for a rational choice of reference isotope have never before been experimentally determined. Here we compare different reference isotopes (and hence distinct experimental designs) using the reduction of dihydrofolate and dihydrobiopterin by two dissimilar enzymes as model reactions. A number of isotopic labeling patterns have been applied to facilitate the comparative study of reference isotopes. The results demonstrate the versatility of the Northrop method and that such experiments are limited only by synthetic techniques, availability of starting materials, and the experimental error associated with the use of distinct combinations of isotopologues.
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Affiliation(s)
- Arundhuti Sen
- The Department of Chemistry, The University of Iowa, Iowa City, Iowa 52242, USA
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Stojković V, Perissinotti LL, Lee J, Benkovic SJ, Kohen A. The effect of active-site isoleucine to alanine mutation on the DHFR catalyzed hydride-transfer. Chem Commun (Camb) 2010; 46:8974-6. [PMID: 20972508 DOI: 10.1039/c0cc02988b] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Comparison of the nature of hydride transfer in wild-type and active site mutant (I14A) of dihydrofolate reductase suggests that the size of this side chain at position 14 modulates H-tunneling.
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Affiliation(s)
- Vanja Stojković
- Department of Chemistry, The University of Iowa, Iowa City, IA, USA
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Characterizing the dynamics of functionally relevant complexes of formate dehydrogenase. Proc Natl Acad Sci U S A 2010; 107:17974-9. [PMID: 20876138 DOI: 10.1073/pnas.0912190107] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The potential for femtosecond to picosecond time-scale motions to influence the rate of the intrinsic chemical step in enzyme-catalyzed reactions is a source of significant controversy. Among the central challenges in resolving this controversy is the difficulty of experimentally characterizing thermally activated motions at this time scale in functionally relevant enzyme complexes. We report a series of measurements to address this problem using two-dimensional infrared spectroscopy to characterize the time scales of active-site motions in complexes of formate dehydrogenase with the transition-state-analog inhibitor azide (N(3)(-)). We observe that the frequency-frequency time correlation functions (FFCF) for the ternary complexes with NAD(+) and NADH decay completely with slow time constants of 3.2 ps and 4.6 ps, respectively. This result suggests that in the vicinity of the transition state, the active-site enzyme structure samples a narrow and relatively rigid conformational distribution indicating that the transition-state structure is well organized for the reaction. In contrast, for the binary complex, we observe a significant static contribution to the FFCF similar to what is seen in other enzymes, indicating the presence of the slow motions that occur on time scales longer than our measurement window.
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