Gray Michael J, Escalante-Semerena Jorge C
Department of Bacteriology, University of Wisconsin, Madison, WI 53706, USA.
J Bacteriol. 2009 Jun;191(12):3842-51. doi: 10.1128/JB.00230-09. Epub 2009 Apr 17.
The genome of Rhodobacter sphaeroides encodes the components of two distinct pathways for salvaging cobinamide (Cbi), a precursor of adenosylcobalamin (AdoCbl, coenzyme B(12)). One pathway, conserved among bacteria, depends on a bifunctional kinase/guanylyltransferase (CobP) enzyme to convert adenosylcobinamide (AdoCbi) to AdoCbi-phosphate (AdoCbi-P), an intermediate in de novo AdoCbl biosynthesis. The other pathway, of archaeal origin, depends on an AdoCbi amidohydrolase (CbiZ) enzyme to generate adenosylcobyric acid (AdoCby), which is converted to AdoCbi-P by the AdoCbi-P synthetase (CobD) enzyme. Here we report that R. sphaeroides strain 2.4.1 synthesizes AdoCbl de novo and that it salvages Cbi using both of the predicted Cbi salvaging pathways. AdoCbl produced by R. sphaeroides was identified and quantified by high-performance liquid chromatography and bioassay. The deletion of cobB (encoding an essential enzyme of the de novo corrin ring biosynthetic pathway) resulted in a strain of R. sphaeroides that would not grow on acetate in the absence of exogenous corrinoids. The results from a nutritional analysis showed that the presence of either CbiZ or CobP was necessary and sufficient for Cbi salvaging, that CbiZ-dependent Cbi salvaging depended on the presence of CobD, and that CobP-dependent Cbi salvaging occurred in a cbiZ(+) strain. Possible reasons why R. sphaeroides maintains two distinct pathways for Cbi salvaging are discussed.
球形红杆菌的基因组编码了两条不同的途径来挽救钴胺酰胺（Cbi），钴胺酰胺是腺苷钴胺素（AdoCbl，辅酶B12）的前体。其中一条途径在细菌中保守，依赖于一种双功能激酶/鸟苷酰转移酶（CobP）将腺苷钴胺酰胺（AdoCbi）转化为腺苷钴胺酰胺磷酸（AdoCbi-P），这是从头合成AdoCbl的中间产物。另一条途径起源于古菌，依赖于腺苷钴胺酰胺酰胺水解酶（CbiZ）生成腺苷钴胺酸（AdoCby），后者由腺苷钴胺酰胺磷酸合成酶（CobD）转化为AdoCbi-P。在此我们报告，球形红杆菌2.4.1菌株能够从头合成AdoCbl，并且它利用两条预测的Cbi挽救途径来挽救Cbi。通过高效液相色谱和生物测定法对球形红杆菌产生的AdoCbl进行了鉴定和定量。cobB（编码从头合成咕啉环生物合成途径的一种必需酶）的缺失导致了一株球形红杆菌，该菌株在没有外源类咕啉的情况下不能在乙酸盐上生长。营养分析结果表明，CbiZ或CobP的存在对于Cbi挽救是必要且充分的，依赖CbiZ的Cbi挽救依赖于CobD的存在，并且依赖CobP的Cbi挽救发生在cbiZ(+)菌株中。讨论了球形红杆菌维持两条不同的Cbi挽救途径的可能原因。
