Methylations in vitamin B biosynthesis and catalysis.

Vitamin B is an essential biomolecule that assists in the catalysis of methyl transfer and radical-based reactions in cellular metabolism. The structure of B is characterized by a tetrapyrrolic corrin ring with a central cobalt ion coordinated with an upper ligand, and a lower ligand anchored via a nucleotide loop. Multiple methyl groups decorate B, and their presence (or absence) have structural and functional consequences. In this minireview, we focus on the methyl groups that distinguish vitamin B from other tetrapyrrolic biomolecules and from its own naturally occurring analogues called cobamides. We draw information from recent advances in the field to understand the origins of these methyl groups and the enzymes that incorporate them, and discuss their biological significance.