1
|
Bhatti T, Kumar A, Parihar A, Moncy HK, Emge TJ, Waldie KM, Hasanayn F, Goldman AS. Metal-Ligand Proton Tautomerism, Electron Transfer, and C(sp 3)-H Activation by a 4-Pyridinyl-Pincer Iridium Hydride Complex. J Am Chem Soc 2023; 145:18296-18306. [PMID: 37552857 PMCID: PMC10450815 DOI: 10.1021/jacs.3c03376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Indexed: 08/10/2023]
Abstract
The para-N-pyridyl-based PCP pincer proligand 3,5-bis(di-tert-butylphosphinomethyl)-2,6-dimethylpyridine (pN-tBuPCP-H) was synthesized and metalated to give the iridium complex (pN-tBuPCP)IrHCl (2-H). In marked contrast with its phenyl-based congeners, e.g., (tBuPCP)IrHCl and derivatives, 2-H is highly air-sensitive and reacts with oxidants such as ferrocenium, trityl cation, and benzoquinone. These oxidations ultimately lead to intramolecular activation of a phosphino-t-butyl C(sp3)-H bond and cyclometalation. Considering the greater electronegativity of N than C, 2-H is expected to be less easily oxidized than simple PCP derivatives; cyclic voltammetry and DFT calculations support this expectation. However, 2-H is calculated to undergo metal-ligand-proton tautomerism (MLPT) to give an N-protonated complex that can be described with resonance forms representing a zwitterionic complex (with a negative charge on Ir) and a p-N-pyridylidene (a remote N-heterocyclic carbene) Ir(I) complex. One-electron oxidation of this tautomer is calculated to be dramatically more favorable than direct oxidation of 2-H (ΔΔG° = -31.3 kcal/mol). The resulting Ir(II) oxidation product is easily deprotonated to give metalloradical 2• which is observed by NMR spectroscopy. 2• can be further oxidized to give cationic Ir(III) complex, 2+, which can oxidatively add a phosphino-t-butyl C-H bond and undergo deprotonation to give the observed cyclometalated product. DFT calculations indicate that less sterically hindered analogues of 2+ would preferentially undergo intermolecular addition of C(sp3)-H bonds, for example, of n-alkanes. The resulting iridium alkyl complexes could undergo facile β-H elimination to afford olefin, thereby completing a catalytic cycle for alkane dehydrogenation driven by one-electron oxidation and deprotonation, enabled by MLPT.
Collapse
Affiliation(s)
- Tariq
M. Bhatti
- Department
of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
| | - Akshai Kumar
- Centre
for Nanotechnology, Indian Institute of
Technology Guwahati, Guwahati 781039, Assam, India
| | - Ashish Parihar
- Department
of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
| | - Hellan K. Moncy
- Department
of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
| | - Thomas J. Emge
- Department
of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
| | - Kate M. Waldie
- Department
of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
| | - Faraj Hasanayn
- Department
of Chemistry, American University of Beirut, Beirut 1107 2020, Lebanon
| | - Alan S. Goldman
- Department
of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
- Centre
for Nanotechnology, Indian Institute of
Technology Guwahati, Guwahati 781039, Assam, India
| |
Collapse
|
2
|
Gatreddi S, Sui D, Hausinger RP, Hu J. Irreversible inactivation of lactate racemase by sodium borohydride reveals reactivity of the nickel-pincer nucleotide cofactor. ACS Catal 2023; 13:1441-1448. [PMID: 37886035 PMCID: PMC10599654 DOI: 10.1021/acscatal.2c05461] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The nickel-pincer nucleotide (NPN) cofactor discovered in lactate racemase from Lactiplantibacillus plantarum (LarALp) is essential for the activities of racemases/epimerases in the highly diverse LarA superfamily. Prior mechanistic studies have established a proton-coupled hydride-transfer mechanism for LarALp, but direct evidence showing that hydride attacks the C4 atom in the pyridinium ring of NPN has been lacking. Here, we show that sodium borohydride (NaBH4) irreversibly inactivates LarALp accompanied by a rapid color change of the enzyme. The altered ultraviolet-visible spectra during NaBH4 titration supported hydride transfer to C4 of NPN, and the concomitant Ni loss unraveled by mass spectrometry experiments accounted for the irreversible inactivation. High resolution structures of LarALp revealed a substantially weakened C-Ni bond in the metastable sulfite-NPN adduct where the NPN cofactor is in the reduced state. These findings allowed us to propose a mechanism of LarALp inactivation by NaBH4 that provides key insights into the enzyme-catalyzed reaction and sheds light on the reactivity of small molecule NPN mimetics.
Collapse
Affiliation(s)
- Santhosh Gatreddi
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, United States
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, United States
| | - Dexin Sui
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, United States
| | - Robert P. Hausinger
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, United States
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, United States
| | - Jian Hu
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, United States
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
| |
Collapse
|
3
|
Aleksanyan DV, Churusova SG, Dubasova EV, Ananyev IV, Artyushin OI, Peregudov AS, Klemenkova ZS, Denisov GL, Kozlov VA. Experimental and computational insights into the direct cyclopalladation of different unsymmetrical, yet closely related pincer ligands with thione sulfur donors. Polyhedron 2023. [DOI: 10.1016/j.poly.2023.116303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
|
4
|
Chatterjee S, Gatreddi S, Gupta S, Nevarez JL, Rankin JA, Turmo A, Hu J, Hausinger RP. Unveiling the mechanisms and biosynthesis of a novel nickel-pincer enzyme. Biochem Soc Trans 2022; 50:1187-1196. [PMID: 35960008 PMCID: PMC9880988 DOI: 10.1042/bst20220490] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 07/28/2022] [Accepted: 07/29/2022] [Indexed: 01/31/2023]
Abstract
The nickel-pincer nucleotide (NPN) coenzyme, a substituted pyridinium mononucleotide that tri-coordinates nickel, was first identified covalently attached to a lysine residue in the LarA protein of lactate racemase. Starting from nicotinic acid adenine dinucleotide, LarB carboxylates C5 of the pyridinium ring and hydrolyzes the phosphoanhydride, LarE converts the C3 and C5 carboxylates to thiocarboxylates, and LarC incorporates nickel to form a C-Ni and two S-Ni bonds, during the biosynthesis of this cofactor. LarB uses a novel carboxylation mechanism involving the transient formation of a cysteinyl-pyridinium adduct. Depending on the source of the enzyme, LarEs either catalyze a sacrificial sulfur transfer from a cysteinyl side chain resulting in the formation of dehydroalanine or they utilize a [4Fe-4S] cluster bound by three cysteine residues to accept and transfer a non-core sulfide atom. LarC is a CTP-dependent enzyme that cytidinylylates its substrate, adds nickel, then hydrolyzes the product to release NPN and CMP. Homologs of the four lar genes are widely distributed in microorganisms, with some species containing multiple copies of larA whereas others lack this gene, consistent with the cofactor serving other functions. Several LarA-like proteins were shown to catalyze racemase or epimerase activities using 2-hydroxyacid substrates other than lactic acid. Thus, lactate racemase is the founding member of a large family of NPN-containing enzymes.
Collapse
Affiliation(s)
- Shramana Chatterjee
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA
| | - Santhosh Gatreddi
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
| | - Swati Gupta
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA
| | - Jorge L. Nevarez
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
| | - Joel A. Rankin
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA
| | - Aiko Turmo
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
| | - Jian Hu
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
- Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
| | - Robert P. Hausinger
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
| |
Collapse
|
5
|
Abstract
At least two types of pincer complexes are known to exist in biology. A metal-pyrroloquinolone quinone (PQQ) cofactor was first identified in bacterial methanol dehydrogenase, and later also found in selected short-chain alcohol dehydrogenases of other microorganisms. The PQQ-associated metal can be calcium, magnesium, or a rare earth element depending on the enzyme sequence. Synthesis of this organic ligand requires a series of accessory proteins acting on a small peptide, PqqA. Binding of metal to PQQ yields an ONO-type pincer complex. More recently, a nickel-pincer nucleotide (NPN) cofactor was discovered in lactate racemase, LarA. This cofactor derives from nicotinic acid adenine dinucleotide via action of a carboxylase/hydrolase, sulfur transferase, and nickel insertase, resulting in an SCS-type pincer complex. The NPN cofactor likely occurs in selected other racemases and epimerases of bacteria, archaea, and a few eukaryotes.
Collapse
Affiliation(s)
- Jorge Nevarez
- Department of Chemistry, 578 South Shaw Lane, Michigan State University, East Lansing, Michigan 48824 (USA)
| | - Aiko Turmo
- Department of Biochemistry and Molecular Biology, 603 Wilson Road, Room 212, Michigan State University, East Lansing, Michigan 48824 (USA)
| | - Jian Hu
- Department of Chemistry, 578 South Shaw Lane, Michigan State University, East Lansing, Michigan 48824 (USA).,Department of Biochemistry and Molecular Biology, 603 Wilson Road, Room 212, Michigan State University, East Lansing, Michigan 48824 (USA)
| | - Robert P Hausinger
- Department of Biochemistry and Molecular Biology, 603 Wilson Road, Room 212, Michigan State University, East Lansing, Michigan 48824 (USA).,Department of Microbiology and Molecular Genetics, 567 Wilson Road, 2215 Biomedical Physical Sciences, Michigan State University, East Lansing, Michigan 48824 (USA)
| |
Collapse
|
6
|
Bioinspired Design and Computational Prediction of SCS Nickel Pincer Complexes for Hydrogenation of Carbon Dioxide. Catalysts 2020. [DOI: 10.3390/catal10030319] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Inspired by the structures of the active site of lactate racemase and H2 activation mechanism of mono-iron hydrogenase, we proposed a series of sulphur–carbon–sulphur (SCS) nickel complexes and computationally predicted their potentials for catalytic hydrogenation of CO2. Density functional theory calculations reveal a metal–ligand cooperated mechanism with the participation of a sulfur atom in the SCS pincer ligand as a proton receiver for the heterolytic cleavage of H2. For all newly proposed complexes containing functional groups with different electron-donating and withdrawing abilities in the SCS ligand, the predicted free energy barriers for the hydrogenation of CO2 to formic acid are in a range of 22.2–25.5 kcal/mol in water. Such a small difference in energy barriers indicates limited contributions of those functional groups to the charge density of the metal center. We further explored the catalytic mechanism of the simplest model complex for hydrogenation of formic acid to formaldehyde and obtained a total free energy barrier of 34.6 kcal/mol for the hydrogenation of CO2 to methanol.
Collapse
|
7
|
Shi R, Wodrich MD, Pan H, Tirani FF, Hu X. Functional Models of the Nickel Pincer Nucleotide Cofactor of Lactate Racemase. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201910490] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Renyi Shi
- Laboratory of Inorganic Synthesis and CatalysisInstitute of Chemical Sciences and EngineeringÉcole Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI BCH 3305 Lausanne 1015 Switzerland
| | - Matthew D. Wodrich
- Laboratory of Inorganic Synthesis and CatalysisInstitute of Chemical Sciences and EngineeringÉcole Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI BCH 3305 Lausanne 1015 Switzerland
- Laboratory for Computational Molecular DesignInstitute of Chemical Science and EngineeringEcole Polytechnique Fédérale de Lausanne (EPFL) Lausanne 1015 Switzerland
| | - Hui‐Jie Pan
- Laboratory of Inorganic Synthesis and CatalysisInstitute of Chemical Sciences and EngineeringÉcole Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI BCH 3305 Lausanne 1015 Switzerland
| | - Farzaneh Fadaei Tirani
- Laboratory of Inorganic Synthesis and CatalysisInstitute of Chemical Sciences and EngineeringÉcole Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI BCH 3305 Lausanne 1015 Switzerland
| | - Xile Hu
- Laboratory of Inorganic Synthesis and CatalysisInstitute of Chemical Sciences and EngineeringÉcole Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI BCH 3305 Lausanne 1015 Switzerland
| |
Collapse
|
8
|
Shi R, Wodrich MD, Pan HJ, Tirani FF, Hu X. Functional Models of the Nickel Pincer Nucleotide Cofactor of Lactate Racemase. Angew Chem Int Ed Engl 2019; 58:16869-16872. [PMID: 31535787 DOI: 10.1002/anie.201910490] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Indexed: 11/06/2022]
Abstract
A novel nickel pincer cofactor was recently discovered in lactate racemase. Reported here are three synthetic nickel pincer complexes that are both structural and functional models of the pincer cofactor in lactate racemase. DFT computations suggest the ipso-carbon atom of the pyridinium pincer ligands act as a hydride acceptor for lactate isomerization, whereas an organometallic pathway involving nickel-mediated β-hydride elimination is less favored.
Collapse
Affiliation(s)
- Renyi Shi
- Laboratory of Inorganic Synthesis and Catalysis, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI, BCH 3305, Lausanne, 1015, Switzerland
| | - Matthew D Wodrich
- Laboratory of Inorganic Synthesis and Catalysis, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI, BCH 3305, Lausanne, 1015, Switzerland.,Laboratory for Computational Molecular Design, Institute of Chemical Science and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, 1015, Switzerland
| | - Hui-Jie Pan
- Laboratory of Inorganic Synthesis and Catalysis, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI, BCH 3305, Lausanne, 1015, Switzerland
| | - Farzaneh Fadaei Tirani
- Laboratory of Inorganic Synthesis and Catalysis, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI, BCH 3305, Lausanne, 1015, Switzerland
| | - Xile Hu
- Laboratory of Inorganic Synthesis and Catalysis, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), ISIC-LSCI, BCH 3305, Lausanne, 1015, Switzerland
| |
Collapse
|
9
|
Qiu B, Wang W, Yang X. Computational Prediction of Ammonia-Borane Dehydrocoupling and Transfer Hydrogenation of Ketones and Imines Catalyzed by SCS Nickel Pincer Complexes. Front Chem 2019; 7:627. [PMID: 31572716 PMCID: PMC6753508 DOI: 10.3389/fchem.2019.00627] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2019] [Accepted: 08/30/2019] [Indexed: 11/22/2022] Open
Abstract
Inspired by the catalytic mechanism and active site structure of lactate racemase, three scorpion-like SCS nickel pincer complexes were proposed as potential catalysts for transfer hydrogenation of ketones and imines with ammonia-borane (AB) as the hydrogen source. Density functional theory calculations reveal a stepwise hydride and proton transfer mechanism for the dehydrocoupling of AB and hydrogenation of N-methylacetonimine, and a concerted proton-coupled hydride transfer process for hydrogenation of acetone, acetophenone, and 3-methyl-2-butanone. Among all proposed Ni complexes, the one with symmetric NH2 group on both arms of the SCS pincer ligand has the lowest free energy barrier of 15.0 kcal/mol for dehydrogenation of AB, as well as total free energy barriers of 17.8, 18.2, 18.0, and 18.6 kcal/mol for hydrogenation of acetone, N-methylacetonimine, acetophenone, and 3-methyl-2-butanone, respectively.
Collapse
Affiliation(s)
- Bing Qiu
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Wan Wang
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Xinzheng Yang
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| |
Collapse
|
10
|
Abstract
The advancements of quantum chemical methods and computer power allow detailed mechanistic investigations of metalloenzymes. In particular, both quantum chemical cluster and combined QM/MM approaches have been used, which have been proven to successfully complement experimental studies. This review starts with a brief introduction of nickel-dependent enzymes and then summarizes theoretical studies on the reaction mechanisms of these enzymes, including NiFe hydrogenase, methyl-coenzyme M reductase, nickel CO dehydrogenase, acetyl CoA synthase, acireductone dioxygenase, quercetin 2,4-dioxygenase, urease, lactate racemase, and superoxide dismutase.
Collapse
|
11
|
Computational Design of SCS Nickel Pincer Complexes for the Asymmetric Transfer Hydrogenation of 1-Acetonaphthone. Catalysts 2019. [DOI: 10.3390/catal9010101] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Inspired by the active site structures of lactate racemase and recently reported sulphur–carbon–sulphur (SCS) nickel pincer complexes, a series of scorpion-like SCS nickel pincer complexes with an imidazole tail and asymmetric claws was proposed and examined computationally as potential catalysts for the asymmetric transfer hydrogenation of 1-acetonaphthone. Density functional theory calculations reveal a proton-coupled hydride transfer mechanism for the dehydrogenation of (R)-(+)-1-phenyl-ethanol and the hydrogenation of 1-acetonaphthone to produce (R)-(+)-1-(2-naphthyl)ethanol and (S)-(−)-1-(2-naphthyl)ethanol. Among all proposed Ni complexes, 1Ph is the most active one with a rather low free energy barrier of 24 kcal/mol and high enantioselectivity of near 99% enantiomeric excess (ee) for the hydrogenation of prochiral ketones to chiral alcohols.
Collapse
|
12
|
Hausinger RP, Desguin B, Fellner M, Rankin JA, Hu J. Nickel-pincer nucleotide cofactor. Curr Opin Chem Biol 2018; 47:18-23. [PMID: 30015232 DOI: 10.1016/j.cbpa.2018.06.019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Revised: 06/15/2018] [Accepted: 06/19/2018] [Indexed: 10/28/2022]
Abstract
A novel organometallic cofactor, nickel pyridinium-3,5-dithiocarboxylic acid mononucleotide, was recently discovered in lactate racemase (LarA) of Lactobacillus plantarum. This review summarizes the substantial progress made in uncovering the function of this cofactor as a transient hydride acceptor in the LarA mechanism. The latest developments related to cofactor biosynthesis reveal insights into a pathway in which LarB serves as a nicotinic acid adenine dinucleotide hydrolase/carboxylase, LarE acts as a sacrificial sulfur transferase, and LarC functions as a nickel insertase, forming the nickel-pincer nucleotide cofactor that becomes covalently tethered to LarA in some bacteria. Bioinformatic studies reveal a widespread occurrence of larA, larB, larC, and larE orthologs in microorganisms, and additional roles for the cofactor are considered.
Collapse
Affiliation(s)
- Robert P Hausinger
- Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA; Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
| | - Benoît Desguin
- Institute of Life Sciences, Université catholique de Louvain, B-1348 Louvain-La-Neuve, Belgium
| | - Matthias Fellner
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
| | - Joel A Rankin
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
| | - Jian Hu
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA; Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
| |
Collapse
|
13
|
Zhang T, Zhang X, Chung LW. Computational Insights into the Reaction Mechanisms of Nickel-Catalyzed Hydrofunctionalizations and Nickel-Dependent Enzymes. ASIAN J ORG CHEM 2018. [DOI: 10.1002/ajoc.201700645] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Tonghuan Zhang
- Department of Chemistry; South University of Science and Technology of China (SUSTech); Shenzhen 518055 China
- Lab of Computational Chemistry and Drug Design; Key Laboratory of Chemical Genomics; Peking University Shenzhen Graduate School; Shenzhen 518055 China
| | - Xiaoyong Zhang
- Department of Chemistry; South University of Science and Technology of China (SUSTech); Shenzhen 518055 China
| | - Lung Wa Chung
- Department of Chemistry; South University of Science and Technology of China (SUSTech); Shenzhen 518055 China
| |
Collapse
|
14
|
Rankin JA, Mauban RC, Fellner M, Desguin B, McCracken J, Hu J, Varganov SA, Hausinger RP. Lactate Racemase Nickel-Pincer Cofactor Operates by a Proton-Coupled Hydride Transfer Mechanism. Biochemistry 2018; 57:3244-3251. [PMID: 29489337 DOI: 10.1021/acs.biochem.8b00100] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Lactate racemase (LarA) of Lactobacillus plantarum contains a novel organometallic cofactor with nickel coordinated to a covalently tethered pincer ligand, pyridinium-3-thioamide-5-thiocarboxylic acid mononucleotide, but its function in the enzyme mechanism has not been elucidated. This study presents direct evidence that the nickel-pincer cofactor facilitates a proton-coupled hydride transfer (PCHT) mechanism during LarA-catalyzed lactate racemization. No signal was detected by electron paramagnetic resonance spectroscopy for LarA in the absence or presence of substrate, consistent with a +2 metal oxidation state and inconsistent with a previously proposed proton-coupled electron transfer mechanism. Pyruvate, the predicted intermediate for a PCHT mechanism, was observed in quenched solutions of LarA. A normal substrate kinetic isotope effect ( kH/ kD of 3.11 ± 0.17) was established using 2-α-2H-lactate, further supporting a PCHT mechanism. UV-visible spectroscopy revealed a lactate-induced perturbation of the cofactor spectrum, notably increasing the absorbance at 340 nm, and demonstrated an interaction of the cofactor with the inhibitor sulfite. A crystal structure of LarA provided greater resolution (2.4 Å) than previously reported and revealed sulfite binding to the pyridinium C4 atom of the reduced pincer cofactor, mimicking hydride reduction during a PCHT catalytic cycle. Finally, computational modeling supports hydride transfer to the cofactor at the C4 position or to the nickel atom, but with formation of a nickel-hydride species requiring dissociation of the His200 metal ligand. In aggregate, these studies provide compelling evidence that the nickel-pincer cofactor acts by a PCHT mechanism.
Collapse
Affiliation(s)
| | - Robert C Mauban
- Department of Chemistry , University of Nevada , Reno , Nevada 89557 , United States
| | | | - Benoît Desguin
- Institute of Life Sciences , Université catholique de Louvain , B-1348 Louvain-La-Neuve , Belgium
| | | | | | - Sergey A Varganov
- Department of Chemistry , University of Nevada , Reno , Nevada 89557 , United States
| | | |
Collapse
|