Single-enzyme conversion of FMNH2 to 5,6-dimethylbenzimidazole, the lower ligand of B12
Single-enzyme conversion of FMNH2 to 5,6-dimethylbenzimidazole, the lower ligand of B12
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DOI：
10.1073/pnas.0609270104
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发表时间：
2007-02-20
影响因子：
11.1
通讯作者：
Escalante-Semerena, Jorge C.
中科院分区：
文献类型：
--
作者：
Gray, Michael J.;Escalante-Semerena, Jorge C.
The synthesis of 5,6-dimethylbenzimidazole (DMB), the lower ligand of coenzyme B-12, has remained elusive. We report in vitro and in vivo evidence that the BluB protein of the photosynthetic bacterium Rhodospirillum rubrum, is necessary and sufficient for catalysis of the O-2-dependent conversion of FMNH2 to DMB. The product of the reaction (DMB) was isolated by using reverse-phase high-pressure liquid chromatography, and its identity was established by UV-visible spectroscopy and MS. No metals were detected in homogeneous preparations of BluB, and the enzyme did not affect DMB synthesis from 4,5-dimethylphenylenediamine and ribose-5-phosphate. The effect of the lack of bluB function in R. rubrum was reflected by the impaired ability of a Delta bluB strain to convert Mg-protoporphyrin IX monomethyl ester (MPE) into protochlorophylide, a reaction of the bacteriochlorophyll biosynthetic pathway catalyzed by the MPE-cyclase enzyme present in this bacterium (BchE, EC 1.14.13.81), a predicted coenzyme B-12-dependent enzyme. The growth defect of the Delta bluB strain observed under anoxic photoheterotrophic conditions was corrected by the addition of DMB or B12 to the culture medium or by introducing into the strain a plasmid encoding the wild-type allele of bluB. The findings reported here close an important gap in our understanding of the enzymology of the assembly of coenzyme B-12.
