The cobinamide amidohydrolase (cobyric acid-forming) CbiZ enzyme: A critical activity of the cobamide remodelling system of Rhodobacter sphaeroides

Academic Article


  • The chemical structures of cobamides [cobalamin (Cbl)-like compounds] are the same, except for the lower ligand, which in adenosylcobalamin (AdoCbl) is 5,6-dimethylbenzimidazole, and in adenosylpseudocobalamin (AdopseudoCbl) is adenine. Why the lower ligand of cobamides varies and what the mechanism of lower ligand replacement is are long-standing questions in the field of B 12 biosynthesis. Work reported here uncovers the strategy used by the photosynthetic α-proteobacterium Rhodobacter sphaeroides to procure the cobamide it needs to grow on acetate as a carbon and energy source. On the basis of genetic and biochemical evidence we conclude that, in R. sphaeroides, the activity of the cobyric acid-producing amidohydrolase CbiZ enzyme is essential for the conversion of AdopseudoCbl into AdoCbl, the cobamide needed for the catabolism of acetate. The CbiZ enzyme uses AdopseudoCbl as a substrate, but not AdoCbl. Implications of these findings for cobamide remodelling in R. sphaeroides and in other CbiZ-containing microorganisms are discussed. © 2009 Blackwell Publishing Ltd.
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    Digital Object Identifier (doi)

    Author List

  • Gray MJ; Escalante-Semerena JC
  • Start Page

  • 1198
  • End Page

  • 1210
  • Volume

  • 74
  • Issue

  • 5