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

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Abstract
Summary: ThefmdAandfmdBgenes encoding formamidase and a putative regulatory protein, respectively, from the methylotrophic bacteriumMethylophilus methylotrophuswere recloned with additional flanking DNA (pSW1).fmdC,encoding a weakly hydrophilic protein containing an N-terminal signal sequence, was identified upstream offmdAB.The derived amino acid sequence of mature FmdC (Mr39204) 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 (Mr40000) 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 ofM. methylotrophusunder conditions where these nitrogen sources are present at very low concentration.
Funding Information
  • Collaborative Awards in Science and Engineering studentships