X-ray absorption and resonance Raman studies of methyl-coenzyme M reductase indicating that ligand exchange and macrocycle reduction accompany reductive activation

Qun Tang, Paul E. Carrington, Yih-Chern Horng, Michael J. Maroney, Stephen W. Ragsdale, David F. Bocian

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

Methyl-coenzyme M reductase (MCR) catalyzes methane formation from methyl-coenzyme M (methyl-SCoM) and N-7-mercaptoheptanoylthreonine phosphate (CoBSH). MCR contains a nickel hydrocorphin cofactor at its active site, called cofactor F430. Here we present evidence that the macrocyclic ligand participates in the redox chemistry involved in catalysis. The active form of MCR, the red1 state, is generated by reducing another spectroscopically distinct form called ox1 with titanium(III) citrate. Previous electron paramagnetic resonance (EPR) and 14N electron nuclear double resonance (ENDOR) studies indicate that both the ox1 and red1 states are best described as formally Ni(I) species on the basis of the character of the orbital containing the spin in the two EPR-active species. Herein, X-ray absorption spectroscopic (XAS) and resonance Raman (RR) studies are reported for the inactive (EPR-silent) forms and the red1 and ox1 states of MCR. RR spectra are also reported for isolated cofactor F430 in the reduced, resting, and oxidized states; selected RR data are reported for the 15N and 64Ni isotopomers of the cofactor, both in the intact enzyme and in solution. Small Ni K-edge energy shifts indicate that minimal electron density changes occur at the Ni center during redox cycling of the enzyme. Titrations with Ti(III) indicate a 3-electron reduction of free cofactor F430 to generate a stable Ni(I) state and a 2-electron reduction of Ni(I)-ox1 to Ni(I)-red1. Analyses of the XANES and EXAFS data reveal that both the ox1 and red1 forms are best described as hexacoordinate and that the main difference between ox1 and red1 is the absence of an axial thiolate ligand in the red1 state. The RR data indicate that cofactor F430 undergoes a significant conformational change when it binds to MCR. Furthermore, the vibrational characteristics of the ox1 state and red1 states are significantly different, especially in hydrocorphin ring modes with appreciable C=N stretching character. It is proposed that these differences arise from a 2-electron reduction of the hydrocorphin ring upon conversion to the red1 form. Presumably, the ring-reduction and ligand-exchange reactions reported herein underlie the enhanced activity of MCRred1, the only form of MCR that can react productively with the methyl group of methyl-SCoM.

Original languageEnglish
Pages (from-to)13242-13256
Number of pages15
JournalJournal of the American Chemical Society
Volume124
Issue number44
DOIs
Publication statusPublished - 2002 Nov 6

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Coenzymes
X ray absorption
Ion exchange
Chemical activation
Ligands
Electron Spin Resonance Spectroscopy
X-Rays
Electrons
Paramagnetic resonance
Oxidation-Reduction
Enzymes
Methane
Titanium
Nickel
Catalysis
Titration
Citric Acid
Stretching
Carrier concentration
Oxidoreductases

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

@article{bf86e78b28fe41e6afb171f755ec0d56,
title = "X-ray absorption and resonance Raman studies of methyl-coenzyme M reductase indicating that ligand exchange and macrocycle reduction accompany reductive activation",
abstract = "Methyl-coenzyme M reductase (MCR) catalyzes methane formation from methyl-coenzyme M (methyl-SCoM) and N-7-mercaptoheptanoylthreonine phosphate (CoBSH). MCR contains a nickel hydrocorphin cofactor at its active site, called cofactor F430. Here we present evidence that the macrocyclic ligand participates in the redox chemistry involved in catalysis. The active form of MCR, the red1 state, is generated by reducing another spectroscopically distinct form called ox1 with titanium(III) citrate. Previous electron paramagnetic resonance (EPR) and 14N electron nuclear double resonance (ENDOR) studies indicate that both the ox1 and red1 states are best described as formally Ni(I) species on the basis of the character of the orbital containing the spin in the two EPR-active species. Herein, X-ray absorption spectroscopic (XAS) and resonance Raman (RR) studies are reported for the inactive (EPR-silent) forms and the red1 and ox1 states of MCR. RR spectra are also reported for isolated cofactor F430 in the reduced, resting, and oxidized states; selected RR data are reported for the 15N and 64Ni isotopomers of the cofactor, both in the intact enzyme and in solution. Small Ni K-edge energy shifts indicate that minimal electron density changes occur at the Ni center during redox cycling of the enzyme. Titrations with Ti(III) indicate a 3-electron reduction of free cofactor F430 to generate a stable Ni(I) state and a 2-electron reduction of Ni(I)-ox1 to Ni(I)-red1. Analyses of the XANES and EXAFS data reveal that both the ox1 and red1 forms are best described as hexacoordinate and that the main difference between ox1 and red1 is the absence of an axial thiolate ligand in the red1 state. The RR data indicate that cofactor F430 undergoes a significant conformational change when it binds to MCR. Furthermore, the vibrational characteristics of the ox1 state and red1 states are significantly different, especially in hydrocorphin ring modes with appreciable C=N stretching character. It is proposed that these differences arise from a 2-electron reduction of the hydrocorphin ring upon conversion to the red1 form. Presumably, the ring-reduction and ligand-exchange reactions reported herein underlie the enhanced activity of MCRred1, the only form of MCR that can react productively with the methyl group of methyl-SCoM.",
author = "Qun Tang and Carrington, {Paul E.} and Yih-Chern Horng and Maroney, {Michael J.} and Ragsdale, {Stephen W.} and Bocian, {David F.}",
year = "2002",
month = "11",
day = "6",
doi = "10.1021/ja020314h",
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journal = "Journal of the American Chemical Society",
issn = "0002-7863",
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X-ray absorption and resonance Raman studies of methyl-coenzyme M reductase indicating that ligand exchange and macrocycle reduction accompany reductive activation. / Tang, Qun; Carrington, Paul E.; Horng, Yih-Chern; Maroney, Michael J.; Ragsdale, Stephen W.; Bocian, David F.

In: Journal of the American Chemical Society, Vol. 124, No. 44, 06.11.2002, p. 13242-13256.

Research output: Contribution to journalArticle

TY - JOUR

T1 - X-ray absorption and resonance Raman studies of methyl-coenzyme M reductase indicating that ligand exchange and macrocycle reduction accompany reductive activation

AU - Tang, Qun

AU - Carrington, Paul E.

AU - Horng, Yih-Chern

AU - Maroney, Michael J.

AU - Ragsdale, Stephen W.

AU - Bocian, David F.

PY - 2002/11/6

Y1 - 2002/11/6

N2 - Methyl-coenzyme M reductase (MCR) catalyzes methane formation from methyl-coenzyme M (methyl-SCoM) and N-7-mercaptoheptanoylthreonine phosphate (CoBSH). MCR contains a nickel hydrocorphin cofactor at its active site, called cofactor F430. Here we present evidence that the macrocyclic ligand participates in the redox chemistry involved in catalysis. The active form of MCR, the red1 state, is generated by reducing another spectroscopically distinct form called ox1 with titanium(III) citrate. Previous electron paramagnetic resonance (EPR) and 14N electron nuclear double resonance (ENDOR) studies indicate that both the ox1 and red1 states are best described as formally Ni(I) species on the basis of the character of the orbital containing the spin in the two EPR-active species. Herein, X-ray absorption spectroscopic (XAS) and resonance Raman (RR) studies are reported for the inactive (EPR-silent) forms and the red1 and ox1 states of MCR. RR spectra are also reported for isolated cofactor F430 in the reduced, resting, and oxidized states; selected RR data are reported for the 15N and 64Ni isotopomers of the cofactor, both in the intact enzyme and in solution. Small Ni K-edge energy shifts indicate that minimal electron density changes occur at the Ni center during redox cycling of the enzyme. Titrations with Ti(III) indicate a 3-electron reduction of free cofactor F430 to generate a stable Ni(I) state and a 2-electron reduction of Ni(I)-ox1 to Ni(I)-red1. Analyses of the XANES and EXAFS data reveal that both the ox1 and red1 forms are best described as hexacoordinate and that the main difference between ox1 and red1 is the absence of an axial thiolate ligand in the red1 state. The RR data indicate that cofactor F430 undergoes a significant conformational change when it binds to MCR. Furthermore, the vibrational characteristics of the ox1 state and red1 states are significantly different, especially in hydrocorphin ring modes with appreciable C=N stretching character. It is proposed that these differences arise from a 2-electron reduction of the hydrocorphin ring upon conversion to the red1 form. Presumably, the ring-reduction and ligand-exchange reactions reported herein underlie the enhanced activity of MCRred1, the only form of MCR that can react productively with the methyl group of methyl-SCoM.

AB - Methyl-coenzyme M reductase (MCR) catalyzes methane formation from methyl-coenzyme M (methyl-SCoM) and N-7-mercaptoheptanoylthreonine phosphate (CoBSH). MCR contains a nickel hydrocorphin cofactor at its active site, called cofactor F430. Here we present evidence that the macrocyclic ligand participates in the redox chemistry involved in catalysis. The active form of MCR, the red1 state, is generated by reducing another spectroscopically distinct form called ox1 with titanium(III) citrate. Previous electron paramagnetic resonance (EPR) and 14N electron nuclear double resonance (ENDOR) studies indicate that both the ox1 and red1 states are best described as formally Ni(I) species on the basis of the character of the orbital containing the spin in the two EPR-active species. Herein, X-ray absorption spectroscopic (XAS) and resonance Raman (RR) studies are reported for the inactive (EPR-silent) forms and the red1 and ox1 states of MCR. RR spectra are also reported for isolated cofactor F430 in the reduced, resting, and oxidized states; selected RR data are reported for the 15N and 64Ni isotopomers of the cofactor, both in the intact enzyme and in solution. Small Ni K-edge energy shifts indicate that minimal electron density changes occur at the Ni center during redox cycling of the enzyme. Titrations with Ti(III) indicate a 3-electron reduction of free cofactor F430 to generate a stable Ni(I) state and a 2-electron reduction of Ni(I)-ox1 to Ni(I)-red1. Analyses of the XANES and EXAFS data reveal that both the ox1 and red1 forms are best described as hexacoordinate and that the main difference between ox1 and red1 is the absence of an axial thiolate ligand in the red1 state. The RR data indicate that cofactor F430 undergoes a significant conformational change when it binds to MCR. Furthermore, the vibrational characteristics of the ox1 state and red1 states are significantly different, especially in hydrocorphin ring modes with appreciable C=N stretching character. It is proposed that these differences arise from a 2-electron reduction of the hydrocorphin ring upon conversion to the red1 form. Presumably, the ring-reduction and ligand-exchange reactions reported herein underlie the enhanced activity of MCRred1, the only form of MCR that can react productively with the methyl group of methyl-SCoM.

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U2 - 10.1021/ja020314h

DO - 10.1021/ja020314h

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JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

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