Publications

• The cobC gene of Salmonella typhimurium codes for a novel phosphatase involved in the assembly of the nucleotide loop of cobalamin.

  O'Toole G.A., Trzebiatowski J.R., Escalante-Semerena J.C.

  We report the identification of a new locus, designated cobC, involved in the assembly of the nucleotide loop of cobalamin in Salmonella typhimurium. The cobC gene has been mapped, cloned, and sequenced. DNA sequence analysis suggested that cobC is divergently transcribed from the adjacent cobD ge ... >> More

  We report the identification of a new locus, designated cobC, involved in the assembly of the nucleotide loop of cobalamin in Salmonella typhimurium. The cobC gene has been mapped, cloned, and sequenced. DNA sequence analysis suggested that cobC is divergently transcribed from the adjacent cobD gene and suggests that the regulatory region of these genes overlap. The cobC gene codes for a predicted polypeptide of 26 kDa with striking homology to phosphoglycerate mutase, fructose-2,6-bisphosphatase, and acid phosphatase enzymes. In vitro experiments demonstrated that CobC dephosphorylated the cobalamin biosynthetic intermediate N1-(5-phospho-alpha-D-ribosyl)-5,6-dimethylbenzimidazole to generate N1-alpha-D-ribosyl-5,6-dimethylbenzimidazole. In vivo data showed that the lack of cobC function blocks the synthesis of cobalamin from its precursors cobinamide and 5,6-dimethylbenzimidazole, i.e. it prevents the assembly of the nucleotide loop of cobalamin. Additionally, exogenous N1-alpha-D-ribosyl-5,6-dimethylbenzimidazole rescues the defect of a cobC mutant. We propose that cobC codes for a novel phosphatase whose primary role is in cobalamin biosynthesis. A model for the sequence of biosynthetic steps that assemble the nucleotide loop of cobalamin in S. typhimurium is presented. << Less

  J. Biol. Chem. 269:26503-26511(1994) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Structural and functional characterization of an RNase HI domain from the bifunctional protein Rv2228c from Mycobacterium tuberculosis.

  Watkins H.A., Baker E.N.

  The open reading frame Rv2228c from Mycobacterium tuberculosis is predicted to encode a protein composed of two domains, each with individual functions, annotated through sequence similarity searches. The N-terminal domain is homologous with prokaryotic and eukaryotic RNase H domains and the C-ter ... >> More

  The open reading frame Rv2228c from Mycobacterium tuberculosis is predicted to encode a protein composed of two domains, each with individual functions, annotated through sequence similarity searches. The N-terminal domain is homologous with prokaryotic and eukaryotic RNase H domains and the C-terminal domain with alpha-ribazole phosphatase (CobC). The N-terminal domain of Rv2228c (Rv2228c/N) and the full-length protein were expressed as fusions with maltose binding protein (MBP). Rv2228c/N was shown to have RNase H activity with a hybrid RNA/DNA substrate as well as double-stranded RNase activity. The full-length protein was shown to have additional CobC activity. The crystal structure of the MBP-Rv2228c/N fusion protein was solved by molecular replacement and refined at 2.25-A resolution (R = 0.182; R(free) = 0.238). The protein is monomeric in solution but associates in the crystal to form a dimer. The Rv2228c/N domain has the classic RNase H fold and catalytic machinery but lacks several surface features that play important roles in the cleavage of RNA/DNA hybrids by other RNases H. The absence of either the basic protrusion of some RNases H or the hybrid binding domain of others appears to be compensated by the C-terminal CobC domain in full-length Rv2228c. The double-stranded-RNase activity of Rv2228c/N contrasts with classical RNases H and is attributed to the absence in Rv2228c/N of a key phosphate binding pocket. << Less

  J. Bacteriol. 192:2878-2886(2010) [PubMed] [EuropePMC]

• Reassessment of the late steps of coenzyme B12 synthesis in Salmonella enterica: evidence that dephosphorylation of adenosylcobalamin-5'-phosphate by the CobC phosphatase is the last step of the pathway.

  Zayas C.L., Escalante-Semerena J.C.

  We report that cobC strains of Salmonella enterica serovar Typhimurium are impaired in the ability to salvage cobyric acid (Cby), a de novo corrin ring biosynthetic intermediate, under aerobic growth conditions. In vivo and in vitro evidence support the conclusion that this new phenotype of cobC s ... >> More

  We report that cobC strains of Salmonella enterica serovar Typhimurium are impaired in the ability to salvage cobyric acid (Cby), a de novo corrin ring biosynthetic intermediate, under aerobic growth conditions. In vivo and in vitro evidence support the conclusion that this new phenotype of cobC strains is due to the inability of serovar Typhimurium to dephosphorylate adenosylcobalamin-5'-phosphate (AdoCbl-5'-P), the product of the condensation of alpha-ribazole-5'-phosphate (alpha-RP) and adenosylcobinamide-GDP by the AdoCbl-5'-P synthase (CobS, EC 2.7.8.26) enzyme. Increased flux through the 5,6-dimethylbenzimidazole and cobinamide (Cbi) activation branches of the nucleotide loop assembly pathway in cobC strains restored AdoCbl-5'-P synthesis from Cby in a cobC strain. The rate of the CobS-catalyzed reaction was at least 2 orders of magnitude higher with alpha-RP than with alpha-ribazole as substrate. On the basis of the data reported herein, we conclude that removal of the phosphoryl group from AdoCbl-5'-P is the last step in AdoCbl biosynthesis in serovar Typhimurium and that the reaction is catalyzed by the AdoCbl-5'-P phosphatase (CobC) enzyme. Explanations for the correction of the Cby salvaging phenotype are discussed. << Less

  J. Bacteriol. 189:2210-2218(2007) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.