Monooxygenases, Bacterial: Oxidation of Alkenes

Abstract

Bacteria that grow using alkenes as their carbon and energy source produce monooxygenase enzymes that catalyze the initial step in alkene metabolism: oxygenation of the alkene to give an epoxide functional group. Among the best characterized groups of alkene‐oxidizing enzymes are multicomponent soluble alkene monooxygenases (AkMOs) that have a binuclear iron active site and are homologous to soluble methane monooxygenase (sMMO) from methane‐oxidizing bacteria. AkMOs have attracted attention because of their ability to produce valuable chiral epoxides, often with high enantiomeric excess as well as their capacity to bioremediate pollution caused by chlorinated alkenes such as trichloroethene (TCE). At least one industrial process for epoxide production has been developed using AkMO‐expressing cells as the biocatalyst. AkMOs from Rhodococcus rhodochrous B‐276, Xanthobacter autotrophicus Py2, and Mycobacterium spp. have been characterized biochemically and genetically, and systems for genetic modification and directed evolution have been developed, which open the way to use of genetic methods to manipulate the properties of these potentially very useful enzymes. Other alkene‐utilizing bacteria that elaborate the flavin active‐center styrene monooxygenase also have potential for synthesis of chiral epoxides, especially molecules with aromatic substituents. Di‐iron center monooxygenases, including membrane‐associated enzymes unrelated to the soluble di‐iron AkMOs, from bacteria that do not naturally grow on alkenes also catalyze enantioselective epoxygenation of alkenes. Future genetic improvements in the catalytic properties of stereoselective alkene‐oxidizing enzymes, together with a drive toward less polluting and more renewable technology, may lead to greater commercial exploitation of these enzymes for bioremediation and synthesis of chiral epoxides.