CD and MCD studies of the effects of component B variant binding on the biferrous active site of methane monooxygenase

Nataša Mitić, Jennifer K. Schwartz, Brian J. Brazeau, John D Lipscomb, Edward I. Solomon

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Abstract

The multicomponent soluble form of methane monooxygenase (sMMO) catalyzes the oxidation of methane through the activation of O2 at a nonheme biferrous center in the hydroxylase component, MMOH. Reactivity is limited without binding of the sMMO effector protein, MMOB. Past studies show that mutations of specific MMOB surface residues cause large changes in the rates of individual steps in the MMOH reaction cycle. To define the structural and mechanistic bases for these observations, CD, MCD, and VTVH MCD spectroscopies coupled with ligand-field (LF) calculations are used to elucidate changes occurring near and at the MMOH biferrous cluster upon binding of MMOB and the MMOB variants. Perturbations to both the CD and MCD are observed upon binding wild-type MMOB and the MMOB variant that similarly increases O2 reactivity. MMOB variants that do not greatly increase O2 reactivity fail to cause one or both of these changes. LF calculations indicate that reorientation of the terminal glutamate on Fe2 reproduces the spectral perturbations in MCD. Although this structural change allows O2 to bridge the diiron site and shifts the redox active orbitals for good overlap, it is not sufficient for enhanced O2 reactivity of the enzyme. Binding of the T111Y-MMOB variant to MMOH induces the MCD, but not CD changes, and causes only a small increase in reactivity. Thus, both the geometric rearrangement at Fe2 (observed in MCD) coupled with a more global conformational change that may control O2 access (probed by CD), induced by MMOB binding, are critical factors in the reactivity of sMMO.

Original languageEnglish (US)
Pages (from-to)8386-8397
Number of pages12
JournalBiochemistry
Volume47
Issue number32
DOIs
StatePublished - Aug 12 2008

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methane monooxygenase
Catalytic Domain
Ligands
Methane
Mixed Function Oxygenases
Access control
Oxidation-Reduction
Glutamic Acid
Spectrum Analysis
Chemical activation
Spectroscopy
Oxidation
Mutation
Enzymes
Proteins

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CD and MCD studies of the effects of component B variant binding on the biferrous active site of methane monooxygenase. / Mitić, Nataša; Schwartz, Jennifer K.; Brazeau, Brian J.; Lipscomb, John D; Solomon, Edward I.

In: Biochemistry, Vol. 47, No. 32, 12.08.2008, p. 8386-8397.

Research output: Contribution to journalArticle

Mitić, Nataša ; Schwartz, Jennifer K. ; Brazeau, Brian J. ; Lipscomb, John D ; Solomon, Edward I. / CD and MCD studies of the effects of component B variant binding on the biferrous active site of methane monooxygenase. In: Biochemistry. 2008 ; Vol. 47, No. 32. pp. 8386-8397.
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AB - The multicomponent soluble form of methane monooxygenase (sMMO) catalyzes the oxidation of methane through the activation of O2 at a nonheme biferrous center in the hydroxylase component, MMOH. Reactivity is limited without binding of the sMMO effector protein, MMOB. Past studies show that mutations of specific MMOB surface residues cause large changes in the rates of individual steps in the MMOH reaction cycle. To define the structural and mechanistic bases for these observations, CD, MCD, and VTVH MCD spectroscopies coupled with ligand-field (LF) calculations are used to elucidate changes occurring near and at the MMOH biferrous cluster upon binding of MMOB and the MMOB variants. Perturbations to both the CD and MCD are observed upon binding wild-type MMOB and the MMOB variant that similarly increases O2 reactivity. MMOB variants that do not greatly increase O2 reactivity fail to cause one or both of these changes. LF calculations indicate that reorientation of the terminal glutamate on Fe2 reproduces the spectral perturbations in MCD. Although this structural change allows O2 to bridge the diiron site and shifts the redox active orbitals for good overlap, it is not sufficient for enhanced O2 reactivity of the enzyme. Binding of the T111Y-MMOB variant to MMOH induces the MCD, but not CD changes, and causes only a small increase in reactivity. Thus, both the geometric rearrangement at Fe2 (observed in MCD) coupled with a more global conformational change that may control O2 access (probed by CD), induced by MMOB binding, are critical factors in the reactivity of sMMO.

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