A bifunctional protein from Pseudomonas denitrificans carries cobinamide kinase and cobinamide phosphate guanylyltransferase activities

Abstract

The two consecutive activities of the cobalamin biosynthetic pathway that catalyze the conversion of cobinamide to

The CobII and CobIII regions of the cobalamin (vitamin B12) biosynthetic operon of Salmonella typhimurium

“…2 (27). The sequence of these genes is homologous with that of genes of Pseudomonas denitrificans that have been shown to encode enzymes catalyzing reactions involved in joining adenosyl-CBI and DMB (2,4,5,9). These sequences and their analysis will be presented in detail elsewhere (11).…”

cobU-dependent assimilation of nonadenosylated cobinamide in cobA mutants of Salmonella typhimurium

“…The CobU protein has been proposed to have Ado-CBI kinase and GTP:Ado-CBI-P guanylyltransferase activities (4,6,19,21). CobA is likely to be an ATP:corrinoid adenosyltransferase (24).…”

“…The evidence presented here demonstrates that the lesions responsible for this phenotype are alleles of the cobU gene, the promoter-proximal gene of the CoblIl region. Specifically, the CobU protein is proposed to catalyze the synthesis of Ado-CBI-GDP from Ado-CBI (4,6,19,21).…”

“…Three genes, designated cobU, cobS, and cobT, have been proposed to encompass this region (21). Of direct relevance to this report is the cobU gene, whose gene product is approximately 40% identical at the amino acid sequence level to the CobP protein of Pseudomonas denitrificans (4,6), with some domains of the proteins greater than 80% identical. In P. denitrificans, the cobP gene encodes a bifunctional enzyme with Ado-CBI kinase, GTP:Ado-CBI-P guanylyltransferase, activities that are needed for the synthesis of Ado-CBI-GDP from Ado-CBI (4,6).…”

“…Of direct relevance to this report is the cobU gene, whose gene product is approximately 40% identical at the amino acid sequence level to the CobP protein of Pseudomonas denitrificans (4,6), with some domains of the proteins greater than 80% identical. In P. denitrificans, the cobP gene encodes a bifunctional enzyme with Ado-CBI kinase, GTP:Ado-CBI-P guanylyltransferase, activities that are needed for the synthesis of Ado-CBI-GDP from Ado-CBI (4,6). The degree of homology between the S. typhimurium CobU and the P. denitrificans CobP makes it likely that the CobU protein carries out the same enzymatic activities (21).…”