An alkane monooxygenase (AlkB) family in which all electron transfer partners are covalently bound to the oxygen-activating hydroxylase.

Alkane monooxygenase (AlkB) is a non-heme diiron enzyme that catalyzes the hydroxylation of alkanes. It is commonly found in alkanotrophic organisms that can live on alkanes as their sole source of carbon and energy. Activation of AlkB occurs via two-electron reduction of its diferric active site, which facilitates the binding, activation, and cleavage of molecular oxygen for insertion into an inert C H bond. Electrons are typically supplied by NADH via a rubredoxin reductase (AlkT) to a rubredoxin (AlkG) to AlkB, although alternative electron transfer partners have been observed. Here we report a family of AlkBs in which both electron transfer partners (a ferredoxin and a ferredoxin reductase) appear as an N-terminal gene fusion to the hydroxylase (ferr_ferrR_AlkB). This enzyme catalyzes the hydroxylation of medium chain alkanes (C6-C14), with a preference for C10-C12. It requires only NADH for activity. It is present in a number of bacteria that are known to be human pathogens. A survey of the genome neighborhoods in which is it found suggest it may be involved in alkane metabolism, perhaps facilitating growth of pathogens in non-host environments. The activity and distribution in biology of alkane monooxygenases that have a fused ferredoxin reductase and ferredoxin are reported. [Display omitted] • Alkane monooxygenases with fused ferredoxin reductase and ferredoxin exist in nature. • These three-domain AlkBs catalyze the hydroxylation of alkanes and require only NADH for activity. • The three-domain AlkBs are misannotated in protein databases, despite being easily identified as an alkane hydroxylase. [ABSTRACT FROM AUTHOR]