Sinorhizobium meliloti bluB is necessary for production of 5,6-dimethylbenzimidazole, the lower ligand of B12

被引:68
作者
Campbell, GRO
Taga, ME
Mistry, K
Lloret, J
Anderson, PJ
Roth, JR
Walker, GC
机构
[1] MIT, Dept Biol, Cambridge, MA 02139 USA
[2] Genentech Inc, San Francisco, CA 94080 USA
[3] Univ Calif Davis, Microbiol Sect, Coll Biol Sci, Davis, CA 95616 USA
关键词
cobalamin; symbiosis; bacteria; vitamin B-12; biosynthesis;
D O I
10.1073/pnas.0509384103
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
An insight into a previously unknown step in B-12 biosynthesis was unexpectedly obtained through our analysis of a mutant of the symbiotic nitrogen fixing bacterium Sinorhizobium meliloti. This mutant was identified based on its unusually bright fluorescence on plates containing the succinoglycan binding dye calcofluor. The mutant contains a Tn5 insertion in a gene that has not been characterized previously in S. meliloti. The closest known homolog is the bluB gene of Rhodobacter capsulatus, which is implicated in the biosynthesis of B-12 (cobalamin). The S. meliloti bluB mutant is unable to grow in minimal media and fails to establish a symbiosis with alfalfa, and these defects can be rescued by the addition of vitamin B-12 (cyanocobalamin) or the lower ligand of cobalamin, 5,6-dimethylbenzimidazole (DMB). Biochemical analysis demonstrated that the bluB mutant does not produce cobalamin unless DMB is supplied. Sequence comparison suggests that BluB is a member of the NADH/flavin mononucleotide (FMN)-dependent nitroreductase family, and we propose that it is involved in the conversion of FMN to DMB.
引用
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页码:4634 / 4639
页数:6
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