Conversion of methane to methanol at the mononuclear and dinuclear copper sites of particulate methane monooxygenase (pMMO): a DFT and QM/MM study.
Methane hydroxylation at the mononuclear and dinuclear copper sites of pMMO is discussed using quantum mechanical and QM/MM calculations. Possible mechanisms are proposed with respect to the formation of reactive copper-oxo and how they activate methane. Dioxygen is incorporated into the Cu(I) species to give a Cu(II)-superoxo species, followed by an H-atom transfer from a tyrosine residue near the monocopper active site. A resultant Cu(II)-hydroperoxo species is next transformed into a Cu(III)-oxo species and a water molecule by the abstraction of an H-atom from another tyrosine residue. This process is accessible in energy under physiological conditions. Dioxygen is also incorporated into the dicopper site to form a (mu-eta(2):eta(2)-peroxo)dicopper species, which is then transformed into a bis(mu-oxo)dicopper species. The formation of this species is more favorable in energy than that of the monocopper-oxo species. The reactivity of the Cu(III)-oxo species is sufficient for the conversion of methane to methanol if it is formed in the protein environment. Since the sigma orbital localized in the Cu-O bond region is singly occupied in the triplet state, this orbital plays a role in the homolytic cleavage of a C-H bond of methane. The reactivity of the bis(mu-oxo)dicopper species is also sufficient for the conversion of methane to methanol. The mixed-valent bis(mu-oxo)Cu(II)Cu(III) species is reactive to methane because the amplitude of the sigma singly occupied MO localized on the bridging oxo moieties plays an essential role in C-H activation.
Yoshizawa
Kazunari
K
Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka 812-8581, Japan. kazunari@ms.ifoc.kyushu-u.ac.jp
Shiota
Yoshihito
Y
D001665:Binding Sites; D003300:Copper / Q000737:chemistry*; D007700:Kinetics; D008697:Methane / Q000737:chemistry / Q000378:metabolism*; D000432:Methanol / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D010105:Oxygenases / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation
D003300:Copper; D010105:Oxygenases; C021555:methane monooxygenase; D008697:Methane; D010100:Oxygen; D000432:Methanol