title: Evidence that a B12-adenosyl transferase is encoded within the ethanolamine operon of Salmonella enterica.
abstract: Adenosylcobalamin (Ado-B12) is both the cofactor and inducer of ethanolamine ammonia lyase (EA-lyase), a catabolic enzyme for ethanolamine. De novo synthesis of Ado-B12 by Salmonella enterica occurs only under anaerobic conditions. Therefore, aerobic growth on ethanolamine requires import of Ado-B12 or a precursor (CN-B12 or OH-B12) that can be adenosylated internally. Several known enzymes adenosylate corrinoids. The CobA enzyme transfers adenosine from ATP to a biosynthetic intermediate in de novo B12 synthesis and to imported CN-B12, OH-B12, or Cbi (a B12 precursor). The PduO adenosyl transferase is encoded in an operon (pdu) for cobalamin-dependent propanediol degradation and is induced by propanediol. Evidence is presented here that a third transferase (EutT) is encoded within the operon for ethanolamine utilization (eut). Surprisingly, these three transferases share no apparent sequence similarity. CobA produces sufficient Ado-B12 to initiate eut operon induction and to serve as a cofactor for EA-lyase when B12 levels are high. Once the eut operon is induced, the EutT transferase supplies more Ado-B12 during the period of high demand. Another protein encoded in the operon (EutA) protects EA-lyase from inhibition by CN-B12 but does so without adenosylation of this corrinoid.
authors.affiliation: Department of Biological Sciences, University of Delaware, Newark, Delaware, USA.
authors.forename: David E
authors.initials: DE
authors.lastname: Sheppard
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Penrod
authors.forename: Thomas
authors.initials: T
authors.lastname: Bobik
authors.forename: Eric
authors.initials: E
authors.lastname: Kofoid
authors.forename: John R
authors.initials: JR
authors.lastname: Roth
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D003038:Cobamides / Q000378:metabolism*; D003470:Culture Media; D019856:Ethanolamine / Q000378:metabolism*; D004981:Ethanolamine Ammonia-Lyase / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D009154:Mutation; D009876:Operon; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
chemical_list: D001426:Bacterial Proteins; D003038:Cobamides; D003470:Culture Media; D019856:Ethanolamine; D019883:Alkyl and Aryl Transferases; C019920:cob(I)alamin adenosyltransferase; D004981:Ethanolamine Ammonia-Lyase; C000913:cobamamide