Dioxygen activation in methane monooxygenase: a theoretical study.
Using broken-symmetry unrestricted Density Functional Theory, the mechanism of enzymatic dioxygen activation by the hydroxylase component of soluble methane monooxygenase (MMOH) is determined to atomic detail. After a thorough examination of mechanistic alternatives, an optimal pathway was identified. The diiron(II) state H(red) reacts with dioxygen to give a ferromagnetically coupled diiron(II,III) H(superoxo) structure, which undergoes intersystem crossing to the antiferromagnetic surface and affords H(peroxo), a symmetric diiron(III) unit with a nonplanar mu-eta(2):eta(2)-O(2)(2)(-) binding mode. Homolytic cleavage of the O-O bond yields the catalytically competent intermediate Q, which has a di (mu-oxo)diiron(IV) core. A carboxylate shift involving Glu243 is essential to the formation of the symmetric H(peroxo) and Q structures. Both thermodynamic and kinetic features agree well with experimental data, and computed spin-exchange coupling constants are in accord with spectroscopic values. Evidence is presented for pH-independent decay of H(red) and H(peroxo). Key electron-transfer steps that occur in the course of generating Q from H(red) are also detailed and interpreted. In contrast to prior theoretical studies, a requisite large model has been employed, electron spins and couplings have been treated in a quantitative manner, potential energy surfaces have been extensively explored, and quantitative total energies have been determined along the reaction pathway.
Department of Chemistry and Center for Biomolecular Simulation, Columbia University, New York, New York 10027, USA.
Benjamin F
BF
Gherman
Mu-Hyun
MH
Baik
Stephen J
SJ
Lippard
Richard A
RA
Friesner
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D020619:Methylococcus capsulatus / Q000201:enzymology; D020602:Methylosinus trichosporium / Q000201:enzymology; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism*; D010105:Oxygenases / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D013816:Thermodynamics
D001426:Bacterial Proteins; D010105:Oxygenases; C021555:methane monooxygenase; D010100:Oxygen