Structural and mutagenesis studies of soluble methane monooxygenase reductase from Methylococcus capsulatus (Bath)

Abstract

The solution structure for the 27 kDa flavin binding domain of soluble methane monooxygenase reductase from Methylococcus capsulatus (Bath) was solved by NMR spectroscopy. The structure consists of a two domains, an FAD binding domain with a six-stranded antiparallel β-barrel and one α-helix, and an NADH binding domain with a five-stranded parallel β-sheet surrounded by four α-helices. The FAD cofactor is bound at the interface between the two domains in a novel conformation. Near this FAD cofactor, a conserved C-terminal phenylalanine residue is proposed to act as a conformational gate for electron transfer. Kinetic studies on a series of mutants confirm that this phenylalanine controls electron transfer by regulating access of NADH substrate to the bound flavin cofactor.