1
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Enos MD, Gavagan M, Jameson N, Zalatan JG, Weis WI. Structural and functional effects of phosphopriming and scaffolding in the kinase GSK-3β. Sci Signal 2024; 17:eado0881. [PMID: 39226374 DOI: 10.1126/scisignal.ado0881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Accepted: 08/02/2024] [Indexed: 09/05/2024]
Abstract
Glycogen synthase kinase 3β (GSK-3β) targets specific signaling pathways in response to distinct upstream signals. We used structural and functional studies to dissect how an upstream phosphorylation step primes the Wnt signaling component β-catenin for phosphorylation by GSK-3β and how scaffolding interactions contribute to this reaction. Our crystal structure of GSK-3β bound to a phosphoprimed β-catenin peptide confirmed the expected binding mode of the phosphoprimed residue adjacent to the catalytic site. An aspartate phosphomimic in the priming site of β-catenin adopted an indistinguishable structure but reacted approximately 1000-fold slower than the native phosphoprimed substrate. This result suggests that substrate positioning alone is not sufficient for catalysis and that native phosphopriming interactions are necessary. We also obtained a structure of GSK-3β with an extended peptide from the scaffold protein Axin that bound with greater affinity than that of previously crystallized Axin fragments. This structure neither revealed additional contacts that produce the higher affinity nor explained how substrate interactions in the GSK-3β active site are modulated by remote Axin binding. Together, our findings suggest that phosphopriming and scaffolding produce small conformational changes or allosteric effects, not captured in the crystal structures, that activate GSK-3β and facilitate β-catenin phosphorylation. These results highlight limitations in our ability to predict catalytic activity from structure and have potential implications for the role of natural phosphomimic mutations in kinase regulation and phosphosite evolution.
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Affiliation(s)
- Michael D Enos
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94035, USA
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94035, USA
| | - Maire Gavagan
- Department of Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Noel Jameson
- Department of Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Jesse G Zalatan
- Department of Chemistry, University of Washington, Seattle, WA 98195, USA
| | - William I Weis
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94035, USA
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94035, USA
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2
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Stitch M, Avagliano D, Graczyk D, Clark IP, González L, Towrie M, Quinn SJ. Good Vibrations Report on the DNA Quadruplex Binding of an Excited State Amplified Ruthenium Polypyridyl IR Probe. J Am Chem Soc 2023; 145:21344-21360. [PMID: 37736878 PMCID: PMC10557146 DOI: 10.1021/jacs.3c06099] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Indexed: 09/23/2023]
Abstract
The nitrile containing Ru(II)polypyridyl complex [Ru(phen)2(11,12-dCN-dppz)]2+ (1) is shown to act as a sensitive infrared probe of G-quadruplex (G4) structures. UV-visible absorption spectroscopy reveals enantiomer sensitive binding for the hybrid htel(K) and antiparallel htel(Na) G4s formed by the human telomer sequence d[AG3(TTAG3)3]. Time-resolved infrared (TRIR) of 1 upon 400 nm excitation indicates dominant interactions with the guanine bases in the case of Λ-1/htel(K), Δ-1/htel(K), and Λ-1/htel(Na) binding, whereas Δ-1/htel(Na) binding is associated with interactions with thymine and adenine bases in the loop. The intense nitrile transient at 2232 cm-1 undergoes a linear shift to lower frequency as the solution hydrogen bonding environment decreases in DMSO/water mixtures. This shift is used as a sensitive reporter of the nitrile environment within the binding pocket. The lifetime of 1 in D2O (ca. 100 ps) is found to increase upon DNA binding, and monitoring of the nitrile and ligand transients as well as the diagnostic DNA bleach bands shows that this increase is related to greater protection from the solvent environment. Molecular dynamics simulations together with binding energy calculations identify the most favorable binding site for each system, which are in excellent agreement with the observed TRIR solution study. This study shows the power of combining the environmental sensitivity of an infrared (IR) probe in its excited state with the TRIR DNA "site effect" to gain important information about the binding site of photoactive agents and points to the potential of such amplified IR probes as sensitive reporters of biological environments.
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Affiliation(s)
- Mark Stitch
- School
of Chemistry, University College Dublin, Dublin, D04 V1W8, Ireland
| | - Davide Avagliano
- Institute
of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währingerstr. 19, 1090 Vienna, Austria
- Department
of Chemistry, Chemical Physics Theory Group, University of Toronto, 80 St. George St., Toronto, Ontario M5S 3H6, Canada
| | - Daniel Graczyk
- School
of Chemistry, University College Dublin, Dublin, D04 V1W8, Ireland
| | - Ian P. Clark
- Central
Laser Facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0QX, U.K.
| | - Leticia González
- Institute
of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währingerstr. 19, 1090 Vienna, Austria
- Vienna
Research Platform on Accelerating Photoreaction Discovery, University of Vienna, Währingerstr. 19, 1090 Vienna, Austria
| | - Michael Towrie
- Central
Laser Facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0QX, U.K.
| | - Susan J Quinn
- School
of Chemistry, University College Dublin, Dublin, D04 V1W8, Ireland
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3
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Wilson TR, Morgenstern A, Alexandrova AN, Eberhart ME. Bond Bundle Analysis of Ketosteroid Isomerase. J Phys Chem B 2022; 126:9443-9456. [PMID: 36383139 DOI: 10.1021/acs.jpcb.2c03638] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Bond bundle analysis is used to investigate enzymatic catalysis in the ketosteroid isomerase (KSI) active site. We identify the unique bonding regions in five KSI systems, including those exposed to applied oriented electric fields and those with amino acid mutations, and calculate the precise redistribution of electron density and other regional properties that accompanies either enhancement or inhibition of KSI catalytic activity. We find that catalytic enhancement results from promoting both inter- and intra-molecular electron density redistribution, between bond bundles and bond wedges within the KSI-docked substrate molecule, in the forward direction of the catalyzed reaction. Though the redistribution applies to both types of perturbed systems and is thus suggestive of a general catalytic role, we observe that bond properties (e.g., volume vs energy vs electron count) can respond independently and disproportionately depending on the type of perturbation. We conclude that the resulting catalytic enhancement/inhibition proceeds via different mechanisms, where some bond properties are utilized more by one type of perturbation than the other. Additionally, we find that the correlations between bond wedge properties and catalyzed reaction barrier energies are additive to predict those of bond bundles and atomic basins, providing a rigorous grounding for connecting changes in local charge density to resulting shifts in reaction barrier energy.
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Affiliation(s)
- Timothy R Wilson
- Department of Chemistry, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80004, United States
| | - Amanda Morgenstern
- Department of Chemistry & Biochemistry, UCCS, 1420 Austin Bluffs Pkwy, Colorado Springs, Colorado 80918, United States
| | - Anastassia N Alexandrova
- Department of Chemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Los Angeles, California 90095, United States
| | - M E Eberhart
- Department of Chemistry, Colorado School of Mines, 1500 Illinois Street, Golden, Colorado 80004, United States
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4
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Cong Y, Zhai Y, Yang J, Grofe A, Gao J, Li H. Quantum vibration perturbation approach with polyatomic probe in simulating infrared spectra. Phys Chem Chem Phys 2021; 24:1174-1182. [PMID: 34932049 DOI: 10.1039/d1cp04490g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The quantitative prediction of vibrational spectra of chromophore molecules in solution is challenging and numerous methods have been developed. In this work, we present a quantum vibration perturbation (QVP) approach, which is a procedure that combines molecular quantum vibration and molecular dynamics with perturbation theory. In this framework, an initial Newtonian molecular dynamics simulation is performed, followed by a substitution process to embed molecular quantum vibrational wave functions into the trajectory. The instantaneous vibrational frequency shift at each time step is calculated using the Rayleigh-Schrödinger perturbation theory, where the perturbation operator is the difference in the vibrational potential between the reference chromophore and the perturbed chromophore in the environment. Semi-classical statistical mechanics is employed to obtain the spectral lineshape function. We validated our method using HCOOH·nH2O (n = 1-2) clusters and HCOOH aqueous solution as examples. The QVP method can be employed for rapid prediction of the vibrational spectrum of a specific mode in solution.
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Affiliation(s)
- Yang Cong
- Institute of Theoretical Chemistry, College of Chemistry, Jilin University, 2519 Jiefang Road, Changchun 130023, People's Republic of China.
| | - Yu Zhai
- Institute of Theoretical Chemistry, College of Chemistry, Jilin University, 2519 Jiefang Road, Changchun 130023, People's Republic of China.
| | - Jitai Yang
- Institute of Theoretical Chemistry, College of Chemistry, Jilin University, 2519 Jiefang Road, Changchun 130023, People's Republic of China.
| | - Adam Grofe
- Institute of Theoretical Chemistry, College of Chemistry, Jilin University, 2519 Jiefang Road, Changchun 130023, People's Republic of China.
| | - Jiali Gao
- Department of Chemistry and Supercomputing Institute, University of Minnesota, 207 Pleasant Street, SE, Minneapolis, MN 55455, USA. .,Institute of Systems and Physical Biology, Shenzhen Bay Laboratory, Shenzhen 518055, China
| | - Hui Li
- Institute of Theoretical Chemistry, College of Chemistry, Jilin University, 2519 Jiefang Road, Changchun 130023, People's Republic of China.
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5
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Mokhtari DA, Appel MJ, Fordyce PM, Herschlag D. High throughput and quantitative enzymology in the genomic era. Curr Opin Struct Biol 2021; 71:259-273. [PMID: 34592682 PMCID: PMC8648990 DOI: 10.1016/j.sbi.2021.07.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Accepted: 07/23/2021] [Indexed: 12/28/2022]
Abstract
Accurate predictions from models based on physical principles are the ultimate metric of our biophysical understanding. Although there has been stunning progress toward structure prediction, quantitative prediction of enzyme function has remained challenging. Realizing this goal will require large numbers of quantitative measurements of rate and binding constants and the use of these ground-truth data sets to guide the development and testing of these quantitative models. Ground truth data more closely linked to the underlying physical forces are also desired. Here, we describe technological advances that enable both types of ground truth measurements. These advances allow classic models to be tested, provide novel mechanistic insights, and place us on the path toward a predictive understanding of enzyme structure and function.
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Affiliation(s)
- D A Mokhtari
- Department of Biochemistry, Stanford University, Stanford, CA, 94305, USA
| | - M J Appel
- Department of Biochemistry, Stanford University, Stanford, CA, 94305, USA
| | - P M Fordyce
- Department of Bioengineering, Stanford University, Stanford, CA, 94305, USA; ChEM-H Institute, Stanford University, Stanford, CA, 94305, USA; Department of Genetics, Stanford University, Stanford, CA, 94305, USA; Chan Zuckerberg Biohub San Francisco, CA, 94110, USA.
| | - D Herschlag
- Department of Biochemistry, Stanford University, Stanford, CA, 94305, USA; Department of Chemical Engineering, Stanford University, Stanford, CA, 94305, USA; ChEM-H Institute, Stanford University, Stanford, CA, 94305, USA.
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6
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Welborn VV, Head-Gordon T. Fluctuations of Electric Fields in the Active Site of the Enzyme Ketosteroid Isomerase. J Am Chem Soc 2019; 141:12487-12492. [DOI: 10.1021/jacs.9b05323] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Affiliation(s)
- Valerie Vaissier Welborn
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Teresa Head-Gordon
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
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7
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Kent SBH. Novel protein science enabled by total chemical synthesis. Protein Sci 2018; 28:313-328. [PMID: 30345579 DOI: 10.1002/pro.3533] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 10/12/2018] [Accepted: 10/15/2018] [Indexed: 01/01/2023]
Abstract
Chemical synthesis is a well-established method for the preparation in the research laboratory of multiple-tens-of-milligram amounts of correctly folded, high purity protein molecules. Chemically synthesized proteins enable a broad spectrum of novel protein science. Racemic mixtures consisting of d-protein and l-protein enantiomers facilitate crystallization and determination of protein structures by X-ray diffraction. d-Proteins enable the systematic development of unnatural mirror image protein molecules that bind with high affinity to natural protein targets. The d-protein form of a therapeutic target can also be used to screen natural product libraries to identify novel small molecule leads for drug development. Proteins with novel polypeptide chain topologies including branched, circular, linear-loop, and interpenetrating polypeptide chains can be constructed by chemical synthesis. Medicinal chemistry can be applied to optimize the properties of therapeutic protein molecules. Chemical synthesis has been used to redesign glycoproteins and for the a priori design and construction of covalently constrained novel protein scaffolds not found in nature. Versatile and precise labeling of protein molecules by chemical synthesis facilitates effective application of advanced physical methods including multidimensional nuclear magnetic resonance and time-resolved FTIR for the elucidation of protein structure-activity relationships. The chemistries used for total synthesis of proteins have been adapted to making artificial molecular devices and protein-inspired nanomolecular constructs. Research to develop mirror image life in the laboratory is in its very earliest stages, based on the total chemical synthesis of d-protein forms of polymerase enzymes.
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Affiliation(s)
- Stephen B H Kent
- Department of Chemistry and Department of Biochemistry and Molecular Biology; Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois, 60637
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8
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Abstract
Proton transfer plays a crucial role in a variety of biological phenomena. The transformation of nanomaterials in the environment and biology makes probing the potential proton transfer between nanomaterials and biomolecules a crucial issue, but it still remains a significant challenge. Here, we report proton transfer at the interface of graphene oxide (GO) by studying the GO-induced vibrational changes of interfacial water and carboxyl-terminated self-assembled monolayer (SAM) with surface-enhanced infrared absorption spectroscopy. In addition to simply acting as a macromolecular buffer in solution, the GO sheet behaves as a two-dimensional hydrogen-bonded exchangeable proton pool to dissociate and transfer protons at the interface with a suitable Brønsted base pair, which may bear a significant potential toxic origin for biological systems with proton-coupled reactions.
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Affiliation(s)
- Lie Wu
- State Key Lab of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry , Chinese Academy of Sciences , Changchun , 130022 Jilin , China
| | - Xiue Jiang
- State Key Lab of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry , Chinese Academy of Sciences , Changchun , 130022 Jilin , China.,University of Science and Technology of China , Hefei , 230026 Anhui , China
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9
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Pinney MM, Natarajan A, Yabukarski F, Sanchez DM, Liu F, Liang R, Doukov T, Schwans JP, Martinez TJ, Herschlag D. Structural Coupling Throughout the Active Site Hydrogen Bond Networks of Ketosteroid Isomerase and Photoactive Yellow Protein. J Am Chem Soc 2018; 140:9827-9843. [DOI: 10.1021/jacs.8b01596] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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10
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Maguire JB, Boyken SE, Baker D, Kuhlman B. Rapid Sampling of Hydrogen Bond Networks for Computational Protein Design. J Chem Theory Comput 2018; 14:2751-2760. [PMID: 29652499 DOI: 10.1021/acs.jctc.8b00033] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Hydrogen bond networks play a critical role in determining the stability and specificity of biomolecular complexes, and the ability to design such networks is important for engineering novel structures, interactions, and enzymes. One key feature of hydrogen bond networks that makes them difficult to rationally engineer is that they are highly cooperative and are not energetically favorable until the hydrogen bonding potential has been satisfied for all buried polar groups in the network. Existing computational methods for protein design are ill-equipped for creating these highly cooperative networks because they rely on energy functions and sampling strategies that are focused on pairwise interactions. To enable the design of complex hydrogen bond networks, we have developed a new sampling protocol in the molecular modeling program Rosetta that explicitly searches for sets of amino acid mutations that can form self-contained hydrogen bond networks. For a given set of designable residues, the protocol often identifies many alternative sets of mutations/networks, and we show that it can readily be applied to large sets of residues at protein-protein interfaces or in the interior of proteins. The protocol builds on a recently developed method in Rosetta for designing hydrogen bond networks that has been experimentally validated for small symmetric systems but was not extensible to many larger protein structures and complexes. The sampling protocol we describe here not only recapitulates previously validated designs with performance improvements but also yields viable hydrogen bond networks for cases where the previous method fails, such as the design of large, asymmetric interfaces relevant to engineering protein-based therapeutics.
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Affiliation(s)
- Jack B Maguire
- Program in Bioinformatics and Computational Biology , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States
| | - Scott E Boyken
- Department of Biochemistry , University of Washington , Seattle , Washington 98195 , United States.,Institute for Protein Design , University of Washington , Seattle , Washington 98195 , United States
| | - David Baker
- Department of Biochemistry , University of Washington , Seattle , Washington 98195 , United States.,Institute for Protein Design , University of Washington , Seattle , Washington 98195 , United States.,Howard Hughes Medical Institute , University of Washington , Seattle , Washington 98195 , United States
| | - Brian Kuhlman
- Department of Biochemistry and Biophysics , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States.,Lineberger Comprehensive Cancer Center , University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States
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11
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Wang L, Fried SD, Markland TE. Proton Network Flexibility Enables Robustness and Large Electric Fields in the Ketosteroid Isomerase Active Site. J Phys Chem B 2017; 121:9807-9815. [DOI: 10.1021/acs.jpcb.7b06985] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Lu Wang
- Department
of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854, United States
| | - Stephen D. Fried
- Medical Research
Council Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, U.K
| | - Thomas E. Markland
- Department
of Chemistry, Stanford University, Stanford, California 94305, United States
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12
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Siskos MG, Choudhary MI, Gerothanassis IP. Hydrogen Atomic Positions of O-H···O Hydrogen Bonds in Solution and in the Solid State: The Synergy of Quantum Chemical Calculations with ¹H-NMR Chemical Shifts and X-ray Diffraction Methods. Molecules 2017; 22:E415. [PMID: 28272366 PMCID: PMC6155303 DOI: 10.3390/molecules22030415] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 02/27/2017] [Accepted: 03/03/2017] [Indexed: 12/21/2022] Open
Abstract
The exact knowledge of hydrogen atomic positions of O-H···O hydrogen bonds in solution and in the solid state has been a major challenge in structural and physical organic chemistry. The objective of this review article is to summarize recent developments in the refinement of labile hydrogen positions with the use of: (i) density functional theory (DFT) calculations after a structure has been determined by X-ray from single crystals or from powders; (ii) ¹H-NMR chemical shifts as constraints in DFT calculations, and (iii) use of root-mean-square deviation between experimentally determined and DFT calculated ¹H-NMR chemical shifts considering the great sensitivity of ¹H-NMR shielding to hydrogen bonding properties.
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Affiliation(s)
- Michael G Siskos
- Section of Organic Chemistry & Biochemistry, Department of Chemistry, University of Ioannina, Ioannina GR-45110, Greece.
| | - M Iqbal Choudhary
- H.E.J. Research Institute of Chemistry, International Center for Biological and Chemical Sciences, University of Karachi, Karachi 75270, Pakistan.
| | - Ioannis P Gerothanassis
- Section of Organic Chemistry & Biochemistry, Department of Chemistry, University of Ioannina, Ioannina GR-45110, Greece.
- H.E.J. Research Institute of Chemistry, International Center for Biological and Chemical Sciences, University of Karachi, Karachi 75270, Pakistan.
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13
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Alkorta I, Elguero J. Is it possible to use the 31
P chemical shifts of phosphines to measure hydrogen bond acidities (HBA)? A comparative study with the use of the 15
N chemical shifts of amines for measuring HBA. J PHYS ORG CHEM 2017. [DOI: 10.1002/poc.3690] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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14
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Adhikary R, Zimmermann J, Romesberg FE. Transparent Window Vibrational Probes for the Characterization of Proteins With High Structural and Temporal Resolution. Chem Rev 2017; 117:1927-1969. [DOI: 10.1021/acs.chemrev.6b00625] [Citation(s) in RCA: 83] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Ramkrishna Adhikary
- Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Jörg Zimmermann
- Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Floyd E. Romesberg
- Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, United States
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15
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Bhatt H, Mishra AK, Murli C, Verma AK, Garg N, Deo MN, Sharma SM. Proton transfer aiding phase transitions in oxalic acid dihydrate under pressure. Phys Chem Chem Phys 2016; 18:8065-74. [PMID: 26924455 DOI: 10.1039/c5cp07442h] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Oxalic acid dihydrate, an important molecular solid in crystal chemistry, ecology and physiology, has been studied for nearly 100 years now. The most debated issues regarding its proton dynamics have arisen due to an unusually short hydrogen bond between the acid and water molecules. Using combined in situ spectroscopic studies and first-principles simulations at high pressures, we show that the structural modification associated with this hydrogen bond is much more significant than ever assumed. Initially, under pressure, proton migration takes place along this strong hydrogen bond at a very low pressure of 2 GPa. This results in the protonation of water with systematic formation of dianionic oxalate and hydronium ion motifs, thus reversing the hydrogen bond hierarchy in the high pressure phase II. The resulting hydrogen bond between a hydronium ion and a carboxylic group shows remarkable strengthening under pressure, even in the pure ionic phase III. The loss of cooperativity of hydrogen bonds leads to another phase transition at ∼ 9 GPa through reorientation of other hydrogen bonds. The high pressure phase IV is stabilized by a strong hydrogen bond between the dominant CO2 and H2O groups of oxalate and hydronium ions, respectively. These findings suggest that oxalate systems may provide useful insights into proton transfer reactions and assembly of simple molecules under extreme conditions.
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Affiliation(s)
- Himal Bhatt
- High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India.
| | - A K Mishra
- High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India.
| | - Chitra Murli
- High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India.
| | - Ashok K Verma
- High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India.
| | - Nandini Garg
- High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India.
| | - M N Deo
- High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India.
| | - Surinder M Sharma
- High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Mumbai, 400 085, India.
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16
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Lamba V, Yabukarski F, Pinney M, Herschlag D. Evaluation of the Catalytic Contribution from a Positioned General Base in Ketosteroid Isomerase. J Am Chem Soc 2016; 138:9902-9. [PMID: 27410422 DOI: 10.1021/jacs.6b04796] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Proton transfer reactions are ubiquitous in enzymes and utilize active site residues as general acids and bases. Crystal structures and site-directed mutagenesis are routinely used to identify these residues, but assessment of their catalytic contribution remains a major challenge. In principle, effective molarity measurements, in which exogenous acids/bases rescue the reaction in mutants lacking these residues, can estimate these catalytic contributions. However, these exogenous moieties can be restricted in reactivity by steric hindrance or enhanced by binding interactions with nearby residues, thereby resulting in over- or underestimation of the catalytic contribution, respectively. With these challenges in mind, we investigated the catalytic contribution of an aspartate general base in ketosteroid isomerase (KSI) by exogenous rescue. In addition to removing the general base, we systematically mutated nearby residues and probed each mutant with a series of carboxylate bases of similar pKa but varying size. Our results underscore the need for extensive and multifaceted variation to assess and minimize steric and positioning effects and determine effective molarities that estimate catalytic contributions. We obtained consensus effective molarities of ∼5 × 10(4) M for KSI from Comamonas testosteroni (tKSI) and ∼10(3) M for KSI from Pseudomonas putida (pKSI). An X-ray crystal structure of a tKSI general base mutant showed no additional structural rearrangements, and double mutant cycles revealed similar contributions from an oxyanion hole mutation in the wild-type and base-rescued reactions, providing no indication of mutational effects extending beyond the general base site. Thus, the high effective molarities suggest a large catalytic contribution associated with the general base. A significant portion of this effect presumably arises from positioning of the base, but its large magnitude suggests the involvement of additional catalytic mechanisms as well.
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Affiliation(s)
- Vandana Lamba
- Department of Biochemistry, ‡Department of Chemistry, #Department of Chemical Engineering, §Stanford ChEM-H, Stanford University , Stanford, California 94305, United States
| | - Filip Yabukarski
- Department of Biochemistry, ‡Department of Chemistry, #Department of Chemical Engineering, §Stanford ChEM-H, Stanford University , Stanford, California 94305, United States
| | - Margaux Pinney
- Department of Biochemistry, ‡Department of Chemistry, #Department of Chemical Engineering, §Stanford ChEM-H, Stanford University , Stanford, California 94305, United States
| | - Daniel Herschlag
- Department of Biochemistry, ‡Department of Chemistry, #Department of Chemical Engineering, §Stanford ChEM-H, Stanford University , Stanford, California 94305, United States
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17
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Cha HJ, Jang DS, Jeong JH, Hong BH, Yun YS, Shin EJ, Choi KY. Role of conserved Met112 residue in the catalytic activity and stability of ketosteroid isomerase. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2016; 1864:1322-7. [PMID: 27375051 DOI: 10.1016/j.bbapap.2016.06.016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2016] [Revised: 06/11/2016] [Accepted: 06/29/2016] [Indexed: 10/21/2022]
Abstract
Ketosteroid isomerase (3-oxosteroid Δ(5)-Δ(4)-isomerase, KSI) from Pseudomonas putida catalyzes allylic rearrangement of the 5,6-double bond of Δ(5)-3-ketosteroid to 4,5-position by stereospecific intramolecular transfer of a proton. The active site of KSI is formed by several hydrophobic residues and three catalytic residues (Tyr14, Asp38, and Asp99). In this study, we investigated the role of a hydrophobic Met112 residue near the active site in the catalysis, steroid binding, and stability of KSI. Replacing Met112 with alanine (yields M112A) or leucine (M112L) decreased the kcat by 20- and 4-fold, respectively. Compared with the wild type (WT), M112A and M112L KSIs showed increased KD values for equilenin, an intermediate analogue; these changes suggest that loss of packing at position 112 might lead to unfavorable steroid binding, thereby resulting in decreased catalytic activity. Furthermore, M112A and M112L mutations reduced melting temperature (Tm) by 6.4°C and 2.5°C, respectively. These changes suggest that favorable packing in the core is important for the maintenance of stability in KSI. The M112K mutation decreased kcat by 2000-fold, compared with the WT. In M112K KSI structure, a new salt bridge was formed between Asp38 and Lys112. This bridge could change the electrostatic potential of Asp38, and thereby contribute to the decreased catalytic activity. The M112K mutation also decreased the stability by reducing Tm by 4.1°C. Our data suggest that the Met112 residue may contribute to the catalytic activity and stability of KSI by providing favorable hydrophobic environments and compact packing in the catalytic core.
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Affiliation(s)
- Hyung Jin Cha
- Pohang Accelerator Laboratory, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
| | - Do Soo Jang
- Department of Life Sciences, POSTECH, Pohang, Republic of Korea
| | - Jae-Hee Jeong
- Pohang Accelerator Laboratory, Pohang University of Science and Technology (POSTECH), Pohang, Republic of Korea
| | - Bee Hak Hong
- Department of Life Sciences, POSTECH, Pohang, Republic of Korea
| | - Young Sung Yun
- Department of Life Sciences, POSTECH, Pohang, Republic of Korea
| | - Eun Ju Shin
- Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea
| | - Kwan Yong Choi
- Department of Life Sciences, POSTECH, Pohang, Republic of Korea.
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18
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Yang W, Wei D, Jin X, Xu C, Geng Z, Guo Q, Ma Z, Dai D, Fan H, Yang X. Effect of the Hydrogen Bond in Photoinduced Water Dissociation: A Double-Edged Sword. J Phys Chem Lett 2016; 7:603-608. [PMID: 26810945 DOI: 10.1021/acs.jpclett.6b00015] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Photoinduced water dissociation on rutile-TiO2 was investigated using various methods. Experimental results reveal that the water dissociation occurs via transferring an H atom to a bridge bonded oxygen site and ejecting an OH radical to the gas phase during irradiation. The reaction is strongly suppressed as the water coverage increases. Further scanning tunneling microscopy study demonstrates that hydrogen bonds between water molecules have a dramatic effect on the reaction. Interestingly, a single hydrogen bond in water dimer enhances the water dissociation reaction, while one-dimensional hydrogen bonds in water chains inhibit the reaction. Density functional theory calculations indicate that the effect of hydrogen bonds on the OH dissociation energy is likely the origin of this remarkable behavior. The results suggest that avoiding a strong hydrogen bond network between water molecules is crucial for water splitting.
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Affiliation(s)
- Wenshao Yang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
| | - Dong Wei
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
| | - Xianchi Jin
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
| | - Chenbiao Xu
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
| | - Zhenhua Geng
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
| | - Qing Guo
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
| | - Zhibo Ma
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
| | - Dongxu Dai
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
| | - Hongjun Fan
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
| | - Xueming Yang
- State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics , 457 Zhongshan Road, Dalian 116023, Liaoning, P. R. China
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19
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Bhatt H, Murli C, Mishra AK, Verma AK, Garg N, Deo MN, Chitra R, Sharma SM. Hydrogen Bond Symmetrization in Glycinium Oxalate under Pressure. J Phys Chem B 2016; 120:851-9. [DOI: 10.1021/acs.jpcb.5b11507] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Himal Bhatt
- High Pressure and Synchrotron Radiation Physics Division, ‡Solid State Physics
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - Chitra Murli
- High Pressure and Synchrotron Radiation Physics Division, ‡Solid State Physics
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - A. K. Mishra
- High Pressure and Synchrotron Radiation Physics Division, ‡Solid State Physics
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - Ashok K. Verma
- High Pressure and Synchrotron Radiation Physics Division, ‡Solid State Physics
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - Nandini Garg
- High Pressure and Synchrotron Radiation Physics Division, ‡Solid State Physics
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - M. N. Deo
- High Pressure and Synchrotron Radiation Physics Division, ‡Solid State Physics
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - R. Chitra
- High Pressure and Synchrotron Radiation Physics Division, ‡Solid State Physics
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
| | - Surinder M. Sharma
- High Pressure and Synchrotron Radiation Physics Division, ‡Solid State Physics
Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
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20
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21
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Wu Y, Fried SD, Boxer SG. Dissecting Proton Delocalization in an Enzyme's Hydrogen Bond Network with Unnatural Amino Acids. Biochemistry 2015; 54:7110-9. [PMID: 26571340 DOI: 10.1021/acs.biochem.5b00958] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Extended hydrogen bond networks are a common structural motif of enzymes. A recent analysis proposed quantum delocalization of protons as a feature present in the hydrogen bond network spanning a triad of tyrosines (Y(16), Y(32), and Y(57)) in the active site of ketosteroid isomerase (KSI), contributing to its unusual acidity and large isotope shift. In this study, we utilized amber suppression to substitute each tyrosine residue with 3-chlorotyrosine to test the delocalization model and the proton affinity balance in the triad. X-ray crystal structures of each variant demonstrated that the structure, notably the O-O distances within the triad, was unaffected by 3-chlorotyrosine substitutions. The changes in the cluster's acidity and the acidity's isotope dependence in these variants were assessed via UV-vis spectroscopy and the proton sharing pattern among individual residues with (13)C nuclear magnetic resonance. Our data show pKa detuning at each triad residue alters the proton delocalization behavior in the H-bond network. The extra stabilization energy necessary for the unusual acidity mainly comes from the strong interactions between Y(57) and Y(16). This is further enabled by Y(32), which maintains the right geometry and matched proton affinity in the triad. This study provides a rich picture of the energetics of the hydrogen bond network in enzymes for further model refinement.
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Affiliation(s)
- Yufan Wu
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
| | - Stephen D Fried
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
| | - Steven G Boxer
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
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22
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List NH, Beerepoot MTP, Olsen JMH, Gao B, Ruud K, Jensen HJA, Kongsted J. Molecular quantum mechanical gradients within the polarizable embedding approach--application to the internal vibrational Stark shift of acetophenone. J Chem Phys 2015; 142:034119. [PMID: 25612701 DOI: 10.1063/1.4905909] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
We present an implementation of analytical quantum mechanical molecular gradients within the polarizable embedding (PE) model to allow for efficient geometry optimizations and vibrational analysis of molecules embedded in large, geometrically frozen environments. We consider a variational ansatz for the quantum region, covering (multiconfigurational) self-consistent-field and Kohn-Sham density functional theory. As the first application of the implementation, we consider the internal vibrational Stark effect of the C=O group of acetophenone in different solvents and derive its vibrational linear Stark tuning rate using harmonic frequencies calculated from analytical gradients and computed local electric fields. Comparisons to PE calculations employing an enlarged quantum region as well as to a non-polarizable embedding scheme show that the inclusion of mutual polarization between acetophenone and water is essential in order to capture the structural modifications and the associated frequency shifts observed in water. For more apolar solvents, a proper description of dispersion and exchange-repulsion becomes increasingly important, and the quality of the optimized structures relies to a larger extent on the quality of the Lennard-Jones parameters.
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Affiliation(s)
- Nanna Holmgaard List
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, Odense DK-5230 Denmark
| | - Maarten T P Beerepoot
- Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø-The Arctic University of Norway, N-9037 Tromsø, Norway
| | - Jógvan Magnus Haugaard Olsen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, Odense DK-5230 Denmark
| | - Bin Gao
- Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø-The Arctic University of Norway, N-9037 Tromsø, Norway
| | - Kenneth Ruud
- Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø-The Arctic University of Norway, N-9037 Tromsø, Norway
| | - Hans Jørgen Aagaard Jensen
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, Odense DK-5230 Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Campusvej 55, Odense M, Odense DK-5230 Denmark
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23
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Siskos MG, Tzakos AG, Gerothanassis IP. Accurate ab initio calculations of O-HO and O-H(-)O proton chemical shifts: towards elucidation of the nature of the hydrogen bond and prediction of hydrogen bond distances. Org Biomol Chem 2015. [PMID: 26196256 DOI: 10.1039/c5ob00920k] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The inability to determine precisely the location of labile protons in X-ray molecular structures has been a key barrier to progress in many areas of molecular sciences. We report an approach for predicting hydrogen bond distances beyond the limits of X-ray crystallography based on accurate ab initio calculations of O-HO proton chemical shifts, using a combination of DFT and contactor-like polarizable continuum model (PCM). Very good linear correlation between experimental and computed (at the GIAO/B3LYP/6-311++G(2d,p) level of theory) chemical shifts were obtained with a large set of 43 compounds in CHCl3 exhibiting intramolecular O-HO and intermolecular and intramolecular ionic O-H(-)O hydrogen bonds. The calculated OH chemical shifts exhibit a strong linear dependence on the computed (O)HO hydrogen bond length, in the region of 1.24 to 1.85 Å, of -19.8 ppm Å(-1) and -20.49 ppm Å(-1) with optimization of the structures at the M06-2X/6-31+G(d) and B3LYP/6-31+G(d) level of theory, respectively. A Natural Bond Orbitals (NBO) analysis demonstrates a very good linear correlation between the calculated (1)H chemical shifts and (i) the second-order perturbation stabilization energies, corresponding to charge transfer between the oxygen lone pairs and σ antibonding orbital and (ii) Wiberg bond order of the O-HO and O-H(-)O hydrogen bond. Accurate ab initio calculations of O-HO and O-H(-)O (1)H chemical shifts can provide improved structural and electronic description of hydrogen bonding and a highly accurate measure of distances of short and strong hydrogen bonds.
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Affiliation(s)
- Michael G Siskos
- Section of Organic Chemistry and Biochemistry, Department of Chemistry, University of Ioannina, Ioannina, GR 45110, Greece.
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24
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Hu F, Wei L, Zheng C, Shen Y, Min W. Live-cell vibrational imaging of choline metabolites by stimulated Raman scattering coupled with isotope-based metabolic labeling. Analyst 2015; 139:2312-7. [PMID: 24555181 DOI: 10.1039/c3an02281a] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Choline is a small molecule that occupies a key position in the biochemistry of all living organisms. Recent studies have strongly implicated choline metabolites in cancer, atherosclerosis and nervous system development. To detect choline and its metabolites, existing physical methods such as magnetic resonance spectroscopy and positron emission tomography are often limited by the poor spatial resolution and substantial radiation dose. Fluorescence imaging, although with submicrometer resolution, requires introduction of bulky fluorophores and thus is difficult in labeling the small choline molecule. By combining the emerging bond-selective stimulated Raman scattering microscopy with metabolic incorporation of deuterated choline, herein we have achieved high resolution imaging of choline-containing metabolites in living mammalian cell lines, primary hippocampal neurons and the multicellular organism C. elegans. Different subcellular distributions of choline metabolites are observed between cancer cells and non-cancer cells, which may reveal a functional difference in the choline metabolism and lipid-mediated signaling events. In neurons, choline incorporation is visualized within both soma and neurites, where choline metabolites are more evenly distributed compared to proteins. Furthermore, choline localization is also observed in the pharynx region of C. elegans larvae, consistent with its organogenesis mechanism. These applications demonstrate the potential of isotope-based stimulated Raman scattering microscopy for future choline-related disease detection and development monitoring in vivo.
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Affiliation(s)
- Fanghao Hu
- Department of Chemistry, Columbia University, 3000 Broadway, New York, NY, USA.
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25
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Joint neutron crystallographic and NMR solution studies of Tyr residue ionization and hydrogen bonding: Implications for enzyme-mediated proton transfer. Proc Natl Acad Sci U S A 2015; 112:5673-8. [PMID: 25902526 DOI: 10.1073/pnas.1502255112] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human carbonic anhydrase II (HCA II) uses a Zn-bound OH(-)/H2O mechanism to catalyze the reversible hydration of CO2. This catalysis also involves a separate proton transfer step, mediated by an ordered solvent network coordinated by hydrophilic residues. One of these residues, Tyr7, was previously shown to be deprotonated in the neutron crystal structure at pH 10. This observation indicated that Tyr7 has a perturbed pKa compared with free tyrosine. To further probe the pKa of this residue, NMR spectroscopic measurements of [(13)C]Tyr-labeled holo HCA II (with active-site Zn present) were preformed to titrate all Tyr residues between pH 5.4-11.0. In addition, neutron studies of apo HCA II (with Zn removed from the active site) at pH 7.5 and holo HCA II at pH 6 were conducted. This detailed interrogation of tyrosines in HCA II by NMR and neutron crystallography revealed a significantly lowered pKa of Tyr7 and how pH and Tyr proximity to Zn affect hydrogen-bonding interactions.
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26
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Wallerstein J, Weininger U, Khan MAI, Linse S, Akke M. Site-specific protonation kinetics of acidic side chains in proteins determined by pH-dependent carboxyl (13)C NMR relaxation. J Am Chem Soc 2015; 137:3093-101. [PMID: 25665463 DOI: 10.1021/ja513205s] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Proton-transfer dynamics plays a critical role in many biochemical processes, such as proton pumping across membranes and enzyme catalysis. The large majority of enzymes utilize acid-base catalysis and proton-transfer mechanisms, where the rates of proton transfer can be rate limiting for the overall reaction. However, measurement of proton-exchange kinetics for individual side-chain carboxyl groups in proteins has been achieved in only a handful of cases, which typically have involved comparative analysis of mutant proteins in the context of reaction network modeling. Here we describe an approach to determine site-specific protonation and deprotonation rate constants (kon and koff, respectively) of carboxyl side chains, based on (13)C NMR relaxation measurements as a function of pH. We validated the method using an extensively studied model system, the B1 domain of protein G, for which we measured rate constants koff in the range (0.1-3) × 10(6) s(-1) and kon in the range (0.6-300) × 10(9) M(-1) s(-1), which correspond to acid-base equilibrium dissociation constants (Ka) in excellent agreement with previous results determined by chemical shift titrations. Our results further reveal a linear free-energy relationship between log kon and pKa, which provides information on the free-energy landscape of the protonation reaction, showing that the variability among residues in these parameters arises primarily from the extent of charge stabilization of the deprotonated state by the protein environment. We find that side-chain carboxyls with extreme values of koff or kon are involved in hydrogen bonding, thus providing a mechanistic explanation for the observed stabilization of the protonated or deprotonated state.
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Affiliation(s)
- Johan Wallerstein
- Department of Biophysical Chemistry and ‡Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University , P.O. Box 124, SE-221 00 Lund, Sweden
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27
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Quantum delocalization of protons in the hydrogen-bond network of an enzyme active site. Proc Natl Acad Sci U S A 2014; 111:18454-9. [PMID: 25503367 DOI: 10.1073/pnas.1417923111] [Citation(s) in RCA: 94] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Enzymes use protein architectures to create highly specialized structural motifs that can greatly enhance the rates of complex chemical transformations. Here, we use experiments, combined with ab initio simulations that exactly include nuclear quantum effects, to show that a triad of strongly hydrogen-bonded tyrosine residues within the active site of the enzyme ketosteroid isomerase (KSI) facilitates quantum proton delocalization. This delocalization dramatically stabilizes the deprotonation of an active-site tyrosine residue, resulting in a very large isotope effect on its acidity. When an intermediate analog is docked, it is incorporated into the hydrogen-bond network, giving rise to extended quantum proton delocalization in the active site. These results shed light on the role of nuclear quantum effects in the hydrogen-bond network that stabilizes the reactive intermediate of KSI, and the behavior of protons in biological systems containing strong hydrogen bonds.
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28
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Ito M, Brinck T. Novel Approach for Identifying Key Residues in Enzymatic Reactions: Proton Abstraction in Ketosteroid Isomerase. J Phys Chem B 2014; 118:13050-8. [DOI: 10.1021/jp508423s] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Mika Ito
- Applied
Physical Chemistry, KTH Royal Institute of Technology, Teknikringen
30, 100 44 Stockholm, Sweden
| | - Tore Brinck
- Applied
Physical Chemistry, KTH Royal Institute of Technology, Teknikringen
30, 100 44 Stockholm, Sweden
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29
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Collette F, Renger T, Schmidt am Busch M. Revealing the functional states in the active site of BLUF photoreceptors from electrochromic shift calculations. J Phys Chem B 2014; 118:11109-19. [PMID: 25153778 PMCID: PMC4174740 DOI: 10.1021/jp506400y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Revised: 08/22/2014] [Indexed: 11/28/2022]
Abstract
Photoexcitation with blue light of the flavin chromophore in BLUF photoreceptors induces a switch into a metastable signaling state that is characterized by a red-shifted absorption maximum. The red shift is due to a rearrangement in the hydrogen bond pattern around Gln63 located in the immediate proximity of the isoalloxazine ring system of the chromophore. There is a long-lasting controversy between two structural models, named Q63A and Q63J in the literature, on the local conformation of the residues Gln63 and Tyr21 in the dark state of the photoreceptor. As regards the mechanistic details of the light-activation mechanism, rotation of Gln63 is opposed by tautomerism in the Q63A and Q63J models, respectively. We provide a structure-based simulation of electrochromic shifts of the flavin chromophore in the wild type and in various site-directed mutants. The excellent overall agreement between experimental and computed data allows us to evaluate the two structural models. Compelling evidence is obtained that the Q63A model is incorrect, whereas the Q63J is fully consistent with the present computations. Finally, we confirm independently that a keto-enol tautomerization of the glutamine at position 63, which was proposed as molecular mechanism for the transition between the dark and the light-adapted state, explains the measured 10 to 15 nm red shift in flavin absorption between these two states of the protein. We believe that the accurateness of our results provides evidence that the BLUF photoreceptors absorption is fine-tuned through electrostatic interactions between the chromophore and the protein matrix, and finally that the simplicity of our theoretical model is advantageous as regards easy reproducibility and further extensions.
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Affiliation(s)
- Florimond Collette
- Institut für Theoretische
Physik, Johannes Kepler Universität
Linz, Altenberger Strasse
69, 4040 Linz, Austria
| | - Thomas Renger
- Institut für Theoretische
Physik, Johannes Kepler Universität
Linz, Altenberger Strasse
69, 4040 Linz, Austria
| | - Marcel Schmidt am Busch
- Institut für Theoretische
Physik, Johannes Kepler Universität
Linz, Altenberger Strasse
69, 4040 Linz, Austria
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30
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Oltrogge LM, Wang Q, Boxer SG. Ground-state proton transfer kinetics in green fluorescent protein. Biochemistry 2014; 53:5947-57. [PMID: 25184668 PMCID: PMC4172208 DOI: 10.1021/bi500147n] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Proton
transfer plays an important role in the optical properties
of green fluorescent protein (GFP). While much is known about excited-state
proton transfer reactions (ESPT) in GFP occurring on ultrafast time
scales, comparatively little is understood about the factors governing
the rates and pathways of ground-state proton transfer. We have utilized
a specific isotopic labeling strategy in combination with one-dimensional 13C nuclear magnetic resonance (NMR) spectroscopy to install
and monitor a 13C directly adjacent to the GFP chromophore
ionization site. The chemical shift of this probe is highly sensitive
to the protonation state of the chromophore, and the resulting spectra
reflect the thermodynamics and kinetics of the proton transfer in
the NMR line shapes. This information is complemented by time-resolved
NMR, fluorescence correlation spectroscopy, and steady-state absorbance
and fluorescence measurements to provide a picture of chromophore
ionization reactions spanning a wide time domain. Our findings indicate
that proton transfer in GFP is described well by a two-site model
in which the chromophore is energetically coupled to a secondary site,
likely the terminal proton acceptor of ESPT, Glu222. Additionally,
experiments on a selection of GFP circular permutants suggest an important
role played by the structural dynamics of the seventh β-strand
in gating proton transfer from bulk solution to the buried chromophore.
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Affiliation(s)
- Luke M Oltrogge
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
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31
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Saggu M, Carter B, Zhou X, Faries K, Cegelski L, Holten D, Boxer SG, Kirmaier C. Putative hydrogen bond to tyrosine M208 in photosynthetic reaction centers from Rhodobacter capsulatus significantly slows primary charge separation. J Phys Chem B 2014; 118:6721-32. [PMID: 24902471 PMCID: PMC4064694 DOI: 10.1021/jp503422c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
![]()
Slow, ∼50
ps, P* → P+HA– electron
transfer is observed in Rhodobacter
capsulatus reaction centers (RCs) bearing the native
Tyr residue at M208 and the single amino acid change of isoleucine
at M204 to glutamic acid. The P* decay kinetics are unusually homogeneous
(single exponential) at room temperature. Comparative solid-state
NMR of [4′-13C]Tyr labeled wild-type and M204E RCs
show that the chemical shift of Tyr M208 is significantly altered
in the M204E mutant and in a manner consistent with formation of a
hydrogen bond to the Tyr M208 hydroxyl group. Models based on RC crystal
structure coordinates indicate that if such a hydrogen bond is formed
between the Glu at M204 and the M208 Tyr hydroxyl group, the −OH
would be oriented in a fashion expected (based on the calculations
by Alden et al., J. Phys. Chem.1996, 100, 16761–16770) to destabilize P+BA– in free energy. Alteration
of the environment of Tyr M208 and BA by Glu M204 via this
putative hydrogen bond has a powerful influence on primary charge
separation.
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Affiliation(s)
- Miguel Saggu
- Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States
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32
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Schwans JP, Sunden F, Gonzalez A, Tsai Y, Herschlag D. Uncovering the determinants of a highly perturbed tyrosine pKa in the active site of ketosteroid isomerase. Biochemistry 2013; 52:7840-55. [PMID: 24151972 PMCID: PMC3890242 DOI: 10.1021/bi401083b] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Within the idiosyncratic enzyme active-site environment, side chain and ligand pKa values can be profoundly perturbed relative to their values in aqueous solution. Whereas structural inspection of systems has often attributed perturbed pKa values to dominant contributions from placement near charged groups or within hydrophobic pockets, Tyr57 of a Pseudomonas putida ketosteroid isomerase (KSI) mutant, suggested to have a pKa perturbed by nearly 4 units to 6.3, is situated within a solvent-exposed active site devoid of cationic side chains, metal ions, or cofactors. Extensive comparisons among 45 variants with mutations in and around the KSI active site, along with protein semisynthesis, (13)C NMR spectroscopy, absorbance spectroscopy, and X-ray crystallography, was used to unravel the basis for this perturbed Tyr pKa. The results suggest that the origin of large energetic perturbations are more complex than suggested by visual inspection. For example, the introduction of positively charged residues near Tyr57 raises its pKa rather than lowers it; this effect, and part of the increase in the Tyr pKa from the introduction of nearby anionic groups, arises from accompanying active-site structural rearrangements. Other mutations with large effects also cause structural perturbations or appear to displace a structured water molecule that is part of a stabilizing hydrogen-bond network. Our results lead to a model in which three hydrogen bonds are donated to the stabilized ionized Tyr, with these hydrogen-bond donors, two Tyr side chains, and a water molecule positioned by other side chains and by a water-mediated hydrogen-bond network. These results support the notion that large energetic effects are often the consequence of multiple stabilizing interactions rather than a single dominant interaction. Most generally, this work provides a case study for how extensive and comprehensive comparisons via site-directed mutagenesis in a tight feedback loop with structural analysis can greatly facilitate our understanding of enzyme active-site energetics. The extensive data set provided may also be a valuable resource for those wishing to extensively test computational approaches for determining enzymatic pKa values and energetic effects.
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Affiliation(s)
- Jason P. Schwans
- Department of Biochemistry, Stanford University, Stanford, California 94305
| | - Fanny Sunden
- Department of Biochemistry, Stanford University, Stanford, California 94305
| | - Ana Gonzalez
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025
| | - Yingssu Tsai
- Department of Chemistry, Stanford University, Stanford, California 94305
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025
| | - Daniel Herschlag
- Department of Biochemistry, Stanford University, Stanford, California 94305
- Department of Chemistry, Stanford University, Stanford, California 94305
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Thermodynamic framework for identifying free energy inventories of enzyme catalytic cycles. Proc Natl Acad Sci U S A 2013; 110:12271-6. [PMID: 23840058 DOI: 10.1073/pnas.1310964110] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Pauling's suggestion that enzymes are complementary in structure to the activated complexes of the reactions they catalyze has provided the conceptual basis to explain how enzymes obtain their fantastic catalytic prowess, and has served as a guiding principle in drug design for over 50 y. However, this model by itself fails to predict the magnitude of enzymes' rate accelerations. We construct a thermodynamic framework that begins with the classic concept of differential binding but invokes additional terms that are needed to account for subtle effects in the catalytic cycle's proton inventory. Although the model presented can be applied generally, this analysis focuses on ketosteroid isomerase (KSI) as an example, where recent experiments along with a large body of kinetic and thermodynamic data have provided strong support for the noncanonical thermodynamic contribution described. The resulting analysis precisely predicts the free energy barrier of KSI's reaction as determined from transition-state theory using only empirical thermodynamic data. This agreement is suggestive that a complete free energy inventory of the KSI catalytic cycle has been identified.
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