O'Toole G A, Trzebiatowski J R, Escalante-Semerena J C
Department of Bacteriology, University of Wisconsin, Madison 53706.
J Biol Chem. 1994 Oct 21;269(42):26503-11.
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.
我们报告了一个新基因座的鉴定，命名为cobC，它参与鼠伤寒沙门氏菌中钴胺素核苷酸环的组装。cobC基因已被定位、克隆和测序。DNA序列分析表明，cobC与相邻的cobD基因呈反向转录，且这些基因的调控区域存在重叠。cobC基因编码一个预测的26 kDa多肽，与磷酸甘油酸变位酶、果糖-2,6-二磷酸酶和酸性磷酸酶具有显著同源性。体外实验表明，CobC使钴胺素生物合成中间体N1-(5-磷酸-α-D-核糖基)-5,6-二甲基苯并咪唑去磷酸化，生成N1-α-D-核糖基-5,6-二甲基苯并咪唑。体内数据显示，cobC功能缺失会阻断钴胺素从前体物钴胺酰胺和5,6-二甲基苯并咪唑的合成，即它阻止了钴胺素核苷酸环的组装。此外，外源性N1-α-D-核糖基-5,6-二甲基苯并咪唑可挽救cobC突变体的缺陷。我们提出，cobC编码一种新型磷酸酶，其主要作用是参与钴胺素的生物合成。本文还提出了鼠伤寒沙门氏菌中组装钴胺素核苷酸环的生物合成步骤顺序模型。
