The synthetase domains of cobalamin biosynthesis amidotransferases CobB and CobQ belong to a new family of ATP-dependent amidoligases, related to dethiobiotin synthetase

Phosphotransacetylases of Escherichia coli and several other bacteria conta in an additional 350-aa N-terminal fragment that is not required for phosph otransacetylase activity. Sequence analysis of this fragment revealed that it is closely related to a family of ATP-dependent enzymes that also includ es dethiobiotin synthetase and the synthetase domains of two amidotransfera ses involved in cobalamin biosynthesis, cobyrinic acid a,c-diamide synthase (CobB) and cobyric acid synthase (CobQ), Further database searches showed that this enzyme family is also related to the MinD family of ATPases invol ved in regulation of cell division in bacteria and archaea. Analysis of seq uence conservation in the members of this enzyme family using the structure of dethiobiotin synthetase active site as a guide allowed us to suggest a model for the interaction of CobB and CobQ with their respective substrates . CobB and CobQ were also found to contain unusual Triad family (class I) g lutamine amidotransferase domains with conserved Cys and His residues, but lacking the Glu residue of the catalytic triad. These results should help i n understanding the enzymology of cobalamin biosynthesis and in resolving t he role of phosphotransacetylase in regulation of the carbon flow to and fr om acetate, Proteins 2000;41:238-247. Published 2000 Wiley-Liss, Inc.dagger