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An outer-membrane porin inducible by short-chain amides and urea in the methylotrophic bacterium Methylophilus methylotrophus

James Mills

Neil R. Wyborn

Steven G. Williams

Department of Biochemistry, University of Leicester, Leicester LE1 7RH, UK

*Author for correspondence: Colin W. Jones. Tel: +44 116 2523 458. Fax: +44 116 2523 369. e-mail: cwj1@le.ac.uk

ABSTRACT

Summary: The fmdA and fmdB genes encoding formamidase and a putative regulatory protein, respectively, from the methylotrophic bacterium Methylophilus methylotrophus were recloned with additional flanking DNA (pSW1). fmdC, encoding a weakly hydrophilic protein containing an N-terminal signal sequence, was identified upstream of fmdAB. The derived amino acid sequence of mature FmdC (M_r 39204) showed that it was rich in -sheet and aromatic amino acids, and exhibited significant similarities to several outer-membrane porins from other bacteria. Cell fractionation studies showed that the protein was located in the outer membrane. Mature FmdC was purified and shown to consist of a single type of subunit (M_r 40000) with the predicted N-terminal amino acid sequence (GATISF-). SDS-PAGE and Western blotting of cells grown in continuous culture under various conditions showed that mature FmdC was induced by formamide, acetamide and urea, repressed by excess ammonia, and over-expressed during prolonged growth under formamide limitation. It is concluded that mature FmdC is a porin involved in the transport of short-chain amides and urea through the outer membrane of M. methylotrophus under conditions where these nitrogen sources are present at very low concentration.

Present address: Therexsys, The Science Park, University of Keele, Keele, Staffs ST5 5SP, UK.

Present address: Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.

Present address: Cantab Pharmaceuticals Research Ltd, Cambridge Science Park, Cambridge CB4 4GN, UK.

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