PMID:8206834

Citation	Trzebiatowski, JR, O'Toole, GA and Escalante-Semerena, JC (1994) The cobT gene of Salmonella typhimurium encodes the NaMN: 5,6-dimethylbenzimidazole phosphoribosyltransferase responsible for the synthesis of N1-(5-phospho-alpha-D-ribosyl)-5,6-dimethylbenzimidazole, an intermediate in the synthesis of the nucleotide loop of cobalamin. J. Bacteriol. 176:3568-75
Abstract	We present in vitro evidence which demonstrates that CobT is the nicotinate nucleotide:5,6-dimethylbenzimidazole (DMB) phosphoribosyltransferase (EC 2.4.2.21) that catalyzes the synthesis of N1-(5-phospho-alpha-D-ribosyl)-5,6-dimethylbenzimidazole, a biosynthetic intermediate of the pathway that assembles the nucleotide loop of cobalamin in Salmonella typhimurium. Mutants previously isolated as DMB auxotrophs are shown by physical and genetic mapping studies and complementation studies to carry lesions in cobT. Explanations for this unexpected phenotype of cobT mutants are discussed. The expected nucleotide loop assembly phenotype of cobT mutants can be observed only in a specific genetic background, i.e., cobB deficient, an observation that is consistent with the existence of an alternative CobT function (G. A. O'Toole, M. R. Rondon, and J. C. Escalante-Semerena, J. Bacteriol. 175:3317-3326, 1993). Computer analysis of CobT homologs showed that at the amino acid level, enteric CobT proteins were 80% identical whereas Pseudomonas denitrificans and Rhizobium meliloti CobT proteins were 95% identical. Interestingly, the degree of identity between enteric and nonenteric CobT homologs was only 30%. The same pattern of homologies was reported for the S. typhimurium CobA, Escherichia coli BtuR, and P. denitrificans CobO proteins (S.-J. Suh and J.C. Escalante-Semerena, Gene 129:93-97, 1993), suggesting evolutionary divergence between the cob genes found in the enteric bacteria E. coli and S. typhimurium and those found in P. denitrificans and R. meliloti.
Links	PubMed PMC205545
Keywords	Amino Acid Sequence; Benzimidazoles/chemistry; Benzimidazoles/metabolism; Chromosome Mapping; Genes, Bacterial/genetics; Molecular Sequence Data; Multienzyme Complexes; Mutation; Nucleotidyltransferases; Pentosyltransferases/genetics; Ribonucleotides/chemistry; Salmonella typhimurium/enzymology; Salmonella typhimurium/genetics; Sequence Homology, Amino Acid; Vitamin B 12/biosynthesis
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
SALTY:COBT		GO:0008939: nicotinate-nucleotide-dimethylbenzimidazole phosphoribosyltransferase activity	ECO:0000314:		F		Figure 2 shows a TLC plate's separation of the reactants and products of the S. typhimurium CobT protein reaction with 2 different cell extracts: one with chromosomally (normal) encoded levels of CobT, and another with overexpressed levels of CobT. The separation indicates that the CobT-overexpressing cells have much greater alpha-ribazole-5'-P and the normal cells have much greater DMB (5,6-dimethylbenzimidazole). The separation indicates that CobT activity catalyzes the reaction from DMB to alpha-ribazole-5'-P, thus demonstrating nicotinate-nucleotide-dimethylbenzimadazole phosphoribosyltransferase activity.	complete CACAO 4863
SALTY:COBT	enables	GO:0008939: nicotinate-nucleotide-dimethylbenzimidazole phosphoribosyltransferase activity	ECO:0000314: direct assay evidence used in manual assertion		F		Seeded From UniProt	complete

References

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