Biochemistry: How to make vitamin B12

Biochemists have worked out the last unknown step involved in the biosynthesis of vitamin B12 (cobalamin). Their discovery, reported in Nature magzine, solves a long-standing puzzle and reveals an unusual bit of biochemistry.
Vitamin B12 is one of the largest known non-polymeric natural products and is the only vitamin that is synthesized exclusively by microorganisms. But despite years of study, the biosynthesis of the lower portion of vitamin B12 is poorly understood.
Graham C. Walker and colleagues have solved the X-ray crystal structure of BluB, an enzyme that is needed in the final stages of vitamin B12 synthesis. They show that the enzyme uses molecular oxygen to cleave another molecule to form 5,6-dimethylbenzimidazole. The 5,6-dimethylbenzimidazole produced in that reaction is then incorporated into vitamin B12 by other enzymes.
The cannibalized molecule is called flavin mononucleotide and it is a cofactor — an organic molecule that binds to an enzyme and is needed for its catalytic activity. The enzymatic destruction of one cofactor to make another is quite unusual, and the authors suggest that BluB represents a new family of enzymes, called 'flavin destructases.'
CONTACT
Graham C. Walker (Massachusetts Institute of Technology, Cambridge, MA, USA)
Please contact co-author:
Christopher T. Walsh (Harvard Medical School, Boston, MA, USA)
Tel: +1 617 432 1715; E-mail: christopher_walsh@hms.harvard.edu
Steven E. Ealick (Cornell University, Ithaca, NY, USA) N&V author
Tel: +1 607 255 7961; E-mail: see3@cornell.edu