Cobalamin (vitamin B(12)) biosynthesis in Rhodobacter capsulatus.
In Rhodobacter capsulatus, cobalamin biosynthesis has been shown to occur when the bacteria are grown either aerobically or anaerobically. However, a comparison of the main cobalamin biosynthetic operon found within R. capsulatus would suggest that the encoded proteins belong to the oxygen-dependent pathway for cobalamin biosynthesis, although, significantly, no homologue of the essential mono-oxygenase CobG has yet been detected. Nonetheless, within this main cob operon is found a large open reading frame termed orf663 that is not found in any other cobalamin biosynthetic operon. When overproduced in Escherichia coli, orf663 was found to encode a 90 kDa integral membrane protein. Some of this protein is cleaved within E. coli to give a soluble N-terminal region that can easily be purified and yields a 50 kDa flavoprotein. When expressed in harness with the genes for precorrin-3a synthesis, ORF663 appears to mediate the transformation of precorrin-3a into a new chromophoric compound. Another open reading frame in close proximity to orf663 is termed orf647, and was found to encode a 2Fe-2S ferredoxin-like protein. We suggest that these two proteins may provide an alternative oxygen-independent mechanism for ring contraction within R. capsulatus.
Queen Mary, University of London, London E1 4NS, UK. H.M.McGoldrick@qmul.ac.uk
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Deery
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D000595:Amino Acid Sequence; D003545:Cysteine; D016366:Open Reading Frames; D009876:Operon; D016354:Rhodobacter capsulatus / Q000235:genetics* / Q000378:metabolism*; D014805:Vitamin B 12 / Q000096:biosynthesis* / Q000235:genetics*
D003545:Cysteine; D014805:Vitamin B 12