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One pathway can incorporate either adenine or dimethylbenzimidazole as {alpha}-axial ligand of B12 cofactors in Salmonella enterica.

Anderson PJ, Lango J, Carkeet C, Britten A, Kräutler B, Hammock BD, Roth JR

Section of Microbiology, University of California, Davis, California, 95616, USA; Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, California, 95616, USA; Department of Nutrition, University of California, Davis, California, 95616-5270, USA; Institute of Organic Chemistry & Centre of Molecular Biosciences, University of Innsbrück, A-6020 Innsbrück, Austria; Department of Entomology & Cancer Research Center, University of California, Davis, California, 95616, USA.

Corrinoid (B12-like)cofactors contain various alpha-axial ligands, including 5,6-dimethylbenzimidazole (DMB) or adenine. The bacterium Salmonella enterica produces the corrin ring only under anaerobic conditions, but can form "complete" corrinoids aerobically by importing an "incomplete" corrinoid such as cobinamide (Cbi) and adding appropriate alpha- and beta-axial ligands. Under aerobic conditions, S. enterica performs the corrinoid-dependent degradation of ethanolamine if given B12, but can make B12 from exogenous Cbi only if DMB is also provided. Mutants isolated for their ability to degrade ethanolamine without added DMB, converted Cbi to pseudo-B12 cofactors (having adenine as alpha-axial ligand). The mutations cause an increase in the level of free adenine and install adenine (instead of DMB) as alpha-ligand. When DMB is provided to these mutants, synthesis of pseudo-B12 cofactors ceases and B12 cofactors are produced, suggesting that DMB regulates production or incorporation of free adenine as alpha-ligand. Wild type cells make pseudo-B12 cofactors during aerobic growth on propanediol plus Cbi and can use pseudovitamin-B12 for all of their corrinoid-dependent enzymes. Synthesis of coenzyme pseudo-B12 cofactors requires the same enzymes (CobT, U, S, C) that install DMB in formation of coenzyme B12. Models are described for the mechanism and control of alpha-axial ligand installation.

Published 5 November 2007 in J Bacteriol.
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