Precorrin-2 C20-methyltransferase, also named CobI or CbiL
Precorrin-2 C20-methyltransferase (also known as S-adenosyl-L-methionine--precorrin-2 methyltransferase) participates in the pathway toward the biosynthesis of cobalamin (vitamin B12). There are two distinct cobalamin biosynthetic pathways in bacteria. The aerobic pathway requires oxygen, and cobalt is inserted late in the pathway; the anaerobic pathway does not require oxygen, and cobalt insertion is the first committed step towards cobalamin synthesis. Precorrin-2 C20-methyltransferase catalyzes methylation at the C-20 position of a cyclic tetrapyrrole ring of precorrin-2 using S-adenosylmethionine as a methyl group source to produce precorrin-3A. In the anaerobic pathway, cobalt is inserted into precorrin-2 by CbiK to generate cobalt-precorrin-2, which is the substrate for CbiL, a C20 methyltransferase. In Clostridium difficile, CbiK and CbiL are fused into a bifunctional enzyme. In the aerobic pathway, the precorrin-2 C20-methyltransferase is named CobI. This family includes CbiL and CobI precorrin-2 C20-methyltransferases, both as stand-alone enzymes and when CbiL forms part of a bifunctional enzyme.
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