Deciphering the oxygen activation mechanism at the CuC site of particulate methane monooxygenase

The enzymatic oxidation of methane to methanol was discovered in methanotrophs over 110 years ago. Nevertheless, the mechanism of action of particulate methane monooxygenase (pMMO) remains elusive, especially regarding O-2 activation and the nature of the active species of the enzyme. Here we decipher the catalytic cycle of pMMO in the presence of the physiological reductant duroquinol (DQH(2)). We demonstrate that O-2 activation is in fact initiated by a Cu-C(ii)-DQH(-) species generated by deprotonation of DQH(2). Our simulations capture the exclusive pathway for the sequential formation of the intermediates, Cu-C(ii)-O-2(center dot-), Cu-C(ii)-OOH- and H2O2, along the O-2 reduction pathway. Furthermore, H2O2 activation by Cu-C(ii)-DQH(-) is initiated by dissociation of DQH(center dot) to yield Cu-C(i), followed by Cu-C(i)-catalysed O-O homolysis, en route to the formation of the Cu-C(ii)-O center dot- species, which is responsible for C-H oxidations. These findings uncover the important roles of the phenol co-substrate for O-2 activation and help resolve the enigmatic mechanism of pMMO.

Automated summary

This study deciphers the catalytic cycle of pMMO in the presence of the physiological reductant duroquinol (DQH(2)), revealing that O-2 activation is initiated by the Cu-C(ii)-DQH(-) species. The research also uncovers the important roles of the phenol co-substrate for O-2 activation.