title: Anaerobic biosynthesis of the lower ligand of vitamin B12.
abstract: Vitamin B12 (cobalamin) is required by humans and other organisms for diverse metabolic processes, although only a subset of prokaryotes is capable of synthesizing B12 and other cobamide cofactors. The complete aerobic and anaerobic pathways for the de novo biosynthesis of B12 are known, with the exception of the steps leading to the anaerobic biosynthesis of the lower ligand, 5,6-dimethylbenzimidazole (DMB). Here, we report the identification and characterization of the complete pathway for anaerobic DMB biosynthesis. This pathway, identified in the obligate anaerobic bacterium Eubacterium limosum, is composed of five previously uncharacterized genes, bzaABCDE, that together direct DMB production when expressed in anaerobically cultured Escherichia coli. Expression of different combinations of the bza genes revealed that 5-hydroxybenzimidazole, 5-methoxybenzimidazole, and 5-methoxy-6-methylbenzimidazole, all of which are lower ligands of cobamides produced by other organisms, are intermediates in the pathway. The bza gene content of several bacterial and archaeal genomes is consistent with experimentally determined structures of the benzimidazoles produced by these organisms, indicating that these genes can be used to predict cobamide structure. The identification of the bza genes thus represents the last remaining unknown component of the biosynthetic pathway for not only B12 itself, but also for three other cobamide lower ligands whose biosynthesis was previously unknown. Given the importance of cobamides in environmental, industrial, and human-associated microbial metabolism, the ability to predict cobamide structure may lead to an improved ability to understand and manipulate microbial metabolism.
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720;
authors.forename: Amrita B
authors.initials: AB
authors.lastname: Hazra
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720;
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Han
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, TX 77843.
authors.forename: Angad P
authors.initials: AP
authors.lastname: Mehta
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720;
authors.forename: Kenny C
authors.initials: KC
authors.lastname: Mok
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720;
authors.forename: Vadim
authors.initials: V
authors.lastname: Osadchiy
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, TX 77843.
authors.forename: Tadhg P
authors.initials: TP
authors.lastname: Begley
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720; taga@berkeley.edu.
authors.forename: Michiko E
authors.initials: ME
authors.lastname: Taga
mesh_terms: D000693:Anaerobiosis; D001105:Archaea / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001562:Benzimidazoles / Q000378:metabolism*; D045728:Corrinoids / Q000096:biosynthesis; D004274:DNA, Recombinant / Q000235:genetics; D004926:Escherichia coli / Q000378:metabolism; D005051:Eubacterium / Q000235:genetics / Q000378:metabolism*; D019766:Genes, Archaeal; D005798:Genes, Bacterial; D045302:Geobacter / Q000235:genetics / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D008969:Molecular Sequence Data; D015394:Molecular Structure; D058845:Moorella / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D011994:Recombinant Proteins / Q000378:metabolism; D058928:Riboswitch / Q000235:genetics; D012486:Salmonella typhimurium / Q000254:growth & development; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D014805:Vitamin B 12 / Q000096:biosynthesis*
chemical_list: D001426:Bacterial Proteins; D001562:Benzimidazoles; D045728:Corrinoids; D004274:DNA, Recombinant; D011994:Recombinant Proteins; D058928:Riboswitch; C015158:5,6-dimethylbenzimidazole; D014805:Vitamin B 12
keywords: 5,6-dimethylbenzimidazole; biosynthesis; cobalamin; cobamide; vitamin B12