The cobinamide amidohydrolase (cobyric acid-forming) CbiZ enzyme: a critical activity of the cobamide remodelling system of Rhodobacter sphaeroides.
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 alpha-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.
Gray
Michael J
MJ
Department of Bacteriology, University of Wisconsin, Madison, WI 53706, USA.
Escalante-Semerena
Jorge C
JC
D000581:Amidohydrolases / Q000235:genetics / Q000378:metabolism*; D001562:Benzimidazoles / Q000378:metabolism; D003038:Cobamides / Q000737:chemistry / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
D001562:Benzimidazoles; D003038:Cobamides; C015158:5,6-dimethylbenzimidazole; D000581:Amidohydrolases