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Appl. Environ. Microbiol. doi:10.1128/AEM.02708-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Discovery of a novel styrene monooxygenase from the metagenome

Laboratory of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands

^* To whom correspondence should be addressed. Email: m.w.fraaije{at}rug.nl.

	Abstract

Oxygenases form an interesting class of biocatalysts as they typically perform oxygenations with exquisite chemo-, regio- and/or enantioselectivity. It has been observed that, once heterologously expressed in Escherichia coli, some oxygenases are able to form the blue pigment indigo. We have exploited this characteristic to screen a metagenomic library derived from loam soil and identified a novel oxygenase. This oxygenase shows 50% sequence identity with styrene monooxygenases from pseudomonads (StyA). Only a limited number of homologs can be found in the genome sequence database indicating that this biocatalyst is member of a relatively small family of bacterial monooxygenases. The newly identified monooxygenase catalyzes the epoxidation of styrene and styrene derivatives and forms the corresponding (S)-epoxides with excellent enantiomeric excess (e.g. (S)-styrene oxide is formed with >99% ee) and therefore is named styrene monooxgenase subunit A (SmoA). SmoA shows high enantioselectivity towards aromatic sulfides (e.g. (R)-ethyl phenyl sulfoxide is formed with 92% ee). This excellent enantioselectivity in combination with the moderate sequence identity forms a clear indication that SmoA from metagenomic origin represents a new enzyme within the small family of styrene monooxygenases.