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Burgmayer SJN, Kirk ML. Advancing Our Understanding of Pyranopterin-Dithiolene Contributions to Moco Enzyme Catalysis. Molecules 2023; 28:7456. [PMID: 38005178 PMCID: PMC10673323 DOI: 10.3390/molecules28227456] [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: 10/03/2023] [Revised: 10/23/2023] [Accepted: 10/24/2023] [Indexed: 11/26/2023] Open
Abstract
The pyranopterin dithiolene ligand is remarkable in terms of its geometric and electronic structure and is uniquely found in mononuclear molybdenum and tungsten enzymes. The pyranopterin dithiolene is found coordinated to the metal ion, deeply buried within the protein, and non-covalently attached to the protein via an extensive hydrogen bonding network that is enzyme-specific. However, the function of pyranopterin dithiolene in enzymatic catalysis has been difficult to determine. This focused account aims to provide an overview of what has been learned from the study of pyranopterin dithiolene model complexes of molybdenum and how these results relate to the enzyme systems. This work begins with a summary of what is known about the pyranopterin dithiolene ligand in the enzymes. We then introduce the development of inorganic small molecule complexes that model aspects of a coordinated pyranopterin dithiolene and discuss the results of detailed physical studies of the models by electronic absorption, resonance Raman, X-ray absorption and NMR spectroscopies, cyclic voltammetry, X-ray crystallography, and chemical reactivity.
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Affiliation(s)
| | - Martin L. Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, Albuquerque, NM 87131, USA
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Kirk ML, Lepluart J, Yang J. Resonance Raman spectroscopy of pyranopterin molybdenum enzymes. J Inorg Biochem 2022; 235:111907. [PMID: 35932756 PMCID: PMC10575615 DOI: 10.1016/j.jinorgbio.2022.111907] [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: 01/30/2022] [Revised: 05/16/2022] [Accepted: 06/16/2022] [Indexed: 10/17/2022]
Abstract
Resonance Raman spectroscopy (rR) is a powerful spectroscopic probe that is widely used for studying the geometric and electronic structure of metalloproteins. In this focused review, we detail how resonance Raman spectroscopy has contributed to a greater understanding of electronic structure, geometric structure, and the reaction mechanisms of pyranopterin molybdenum enzymes. The review focuses on the enzymes sulfite oxidase (SO), dimethyl sulfoxide reductase (DMSOR), xanthine oxidase (XO), and carbon monoxide dehydrogenase. Specifically, we highlight how Mo-Ooxo, Mo-Ssulfido, Mo-Sdithiolene, and dithiolene CC vibrational modes, isotope and heavy atom perturbations, resonance enhancement, and associated Raman studies of small molecule analogs have provided detailed insight into the nature of these metalloenzyme active sites.
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Affiliation(s)
- Martin L Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM 87131-0001, United States.
| | - Jesse Lepluart
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM 87131-0001, United States
| | - Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM 87131-0001, United States
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Kirk ML, Hille R. Spectroscopic Studies of Mononuclear Molybdenum Enzyme Centers. Molecules 2022; 27:molecules27154802. [PMID: 35956757 PMCID: PMC9370002 DOI: 10.3390/molecules27154802] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 06/26/2022] [Accepted: 06/29/2022] [Indexed: 02/06/2023] Open
Abstract
A concise review is provided of the contributions that various spectroscopic methods have made to our understanding of the physical and electronic structures of mononuclear molybdenum enzymes. Contributions to our understanding of the structure and function of each of the major families of these enzymes is considered, providing a perspective on how spectroscopy has impacted the field.
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Affiliation(s)
- Martin L. Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM 87131-0001, USA
- Correspondence: (M.L.K.); (R.H.)
| | - Russ Hille
- Department of Biochemistry, Boyce Hall 1463, University of California, Riverside, CA 82521, USA
- Correspondence: (M.L.K.); (R.H.)
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Aiding a Better Understanding of Molybdopterin: Syntheses, Structures, and pKa Value Determinations of Varied Pterin-Derived Organic Scaffolds Including Oxygen, Sulfur and Phosphorus Bearing Substituents. J Mol Struct 2021. [DOI: 10.1016/j.molstruc.2020.129867] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Kirk ML, Kc K. Molybdenum and Tungsten Cofactors and the Reactions They Catalyze. Met Ions Life Sci 2020; 20:/books/9783110589757/9783110589757-015/9783110589757-015.xml. [PMID: 32851830 PMCID: PMC8176780 DOI: 10.1515/9783110589757-015] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2023]
Abstract
The last 20 years have seen a dramatic increase in our mechanistic understanding of the reactions catalyzed by pyranopterin Mo and W enzymes. These enzymes possess a unique cofactor (Moco) that contains a novel ligand in bioinorganic chemistry, the pyranopterin ene-1,2-dithiolate. A synopsis of Moco biosynthesis and structure is presented, along with our current understanding of the role Moco plays in enzymatic catalysis. Oxygen atom transfer (OAT) reactivity is discussed in terms of breaking strong metal-oxo bonds and the mechanism of OAT catalyzed by enzymes of the sulfite oxidase (SO) family that possess dioxo Mo(VI) active sites. OAT reactivity is also discussed in members of the dimethyl sulfoxide (DMSO) reductase family, which possess des-oxo Mo(IV) sites. Finally, we reveal what is known about hydride transfer reactivity in xanthine oxidase (XO) family enzymes and the formate dehydrogenases. The formal hydride transfer reactivity catalyzed by xanthine oxidase family enzymes is complex and cleaves substrate C-H bonds using a mechanism that is distinct from monooxygenases. The chapter primarily highlights developments in the field that have occurred since ~2000, which have contributed to our collective structural and mechanistic understanding of the three canonical pyranopterin Mo enzymes families: XO, SO, and DMSO reductase.
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Abstract
Here we highlight past work on metal-dithiolene interactions and how the unique electronic structure of the metal-dithiolene unit contributes to both the oxidative and reductive half reactions in pyranopterin molybdenum and tungsten enzymes. The metallodithiolene electronic structures detailed here were interrogated using multiple ground and excited state spectroscopic probes on the enzymes and their small molecule analogs. The spectroscopic results have been interpreted in the context of bonding and spectroscopic calculations, and the pseudo-Jahn-Teller effect. The dithiolene is a unique ligand with respect to its redox active nature, electronic synergy with the pyranopterin component of the molybdenum cofactor, and the ability to undergo chelate ring distortions that control covalency, reduction potential, and reactivity in pyranopterin molybdenum and tungsten enzymes.
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Affiliation(s)
- Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, Albuquerque, NM 87131-0001, USA
| | - John H. Enemark
- Department of Chemistry Biochemistry, University of Arizona, Tucson, AZ 85721, USA
| | - Martin L. Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, Albuquerque, NM 87131-0001, USA
- Correspondence: ; Tel.: +1-505-277-5992
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Ono K, Kitaoka K, Ikeno S, Yonemura T. Crystal structures, spectroscopic studies and photodenitrosylation reactions of stereoselectively formed dinitrosyl-molybdenum [Mo(bidentate-N,S)2(NO)2] complexes with 2-pyrimidinethiolate derivatives. Polyhedron 2019. [DOI: 10.1016/j.poly.2019.02.057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Gisewhite DR, Yang J, Williams BR, Esmail A, Stein B, Kirk ML, Burgmayer SJN. Implications of Pyran Cyclization and Pterin Conformation on Oxidized Forms of the Molybdenum Cofactor. J Am Chem Soc 2018; 140:12808-12818. [PMID: 30200760 DOI: 10.1021/jacs.8b05777] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The large family of mononuclear molybdenum and tungsten enzymes all possess the special ligand molybdopterin (MPT), which consists of a metal-binding dithiolene chelate covalently bound to a pyranopterin group. MPT pyran cyclization/scission processes have been proposed to modulate the reactivity of the metal center during catalysis. We have designed several small-molecule models for the Mo-MPT cofactor that allow detailed investigation into how pyran cyclization modulates electronic communication between the dithiolene and pterin moieties and how this cyclization alters the electronic environment of the molybdenum catalytic site. Using a combination of cyclic voltammetry, vibrational spectroscopy (FT-IR and rR), electronic absorption spectroscopy, and X-ray absorption spectroscopy, distinct changes in the Mo≡O stretching frequency, Mo(V/IV) reduction potential, and electronic structure across the pterin-dithiolene ligand are observed as a function of pyran ring closure. The results are significant, for they reveal that a dihydropyranopterin is electronically coupled into the Mo-dithiolene group due to a coplanar conformation of the pterin and dithiolene units, providing a mechanism for the electron-deficient pterin to modulate the Mo environment. A spectroscopic signature identified for the dihydropyranopterin-dithiolene ligand on Mo is a strong dithiolene → pterin charge transfer transition. In the absence of a pyran group bridge between pterin and dithiolene, the pterin rotates out of plane, largely decoupling the system. The results support a hypothesis that pyran cyclization/scission processes in MPT may function as a molecular switch to electronically couple and decouple the pterin and dithiolene to adjust the redox properties in certain pyranopterin molybdenum enzymes.
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Affiliation(s)
- Douglas R Gisewhite
- Department of Chemistry , Bryn Mawr College , Bryn Mawr , Pennsylvania 19010 , United States
| | - Jing Yang
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC03 2060, 1 University of New Mexico , Albuquerque , New Mexico 87131-0001 , United States
| | - Benjamin R Williams
- Department of Chemistry , Bryn Mawr College , Bryn Mawr , Pennsylvania 19010 , United States
| | - Alisha Esmail
- Department of Chemistry , Bryn Mawr College , Bryn Mawr , Pennsylvania 19010 , United States
| | - Benjamin Stein
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC03 2060, 1 University of New Mexico , Albuquerque , New Mexico 87131-0001 , United States
| | - Martin L Kirk
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC03 2060, 1 University of New Mexico , Albuquerque , New Mexico 87131-0001 , United States
| | - Sharon J N Burgmayer
- Department of Chemistry , Bryn Mawr College , Bryn Mawr , Pennsylvania 19010 , United States
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Yang J, Dong C, Kirk ML. Xanthine oxidase-product complexes probe the importance of substrate/product orientation along the reaction coordinate. Dalton Trans 2017; 46:13242-13250. [PMID: 28696463 PMCID: PMC5634921 DOI: 10.1039/c7dt01728f] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
A combination of reaction coordinate computations, resonance Raman spectroscopy, spectroscopic computations, and hydrogen bonding investigations have been used to understand the importance of substrate orientation along the xanthine oxidase reaction coordinate. Specifically, 4-thiolumazine and 2,4-dithiolumazine have been used as reducing substrates for xanthine oxidase to form stable enzyme-product charge transfer complexes suitable for spectroscopic study. Laser excitation into the near-infrared molybdenum-to-product charge transfer band produces rR enhancement patterns in the high frequency in-plane stretching region that directly probe the nature of this MLCT transition and provide insight into the effects of electron redistribution along the reaction coordinate between the transition state and the stable enzyme-product intermediate, including the role of the covalent Mo-O-C linkage in facilitating this process. The results clearly show that specific Mo-substrate orientations allow for enhanced electronic coupling and facilitate strong hydrogen bonding interactions with amino acid residues in the substrate binding pocket.
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Affiliation(s)
- Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM87131-0001, USA.
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