Abstract
Radical S-adenosylmethionine (SAM) (RS) methylases perform methylation reactions at unactivated carbon and phosphorus atoms. RS enzymes typically abstract a hydrogen from their substrates, generating a substrate-centered radical; class B RS methylases catalyze methyl transfer from SAM to cobalamin and then to a substrate-centered carbon or phosphorus radical. Radle et al. now show that Mmp10, an RS enzyme implicated in the methylation of Arg-285 in methyl coenzyme M reductase, binds a methylcobalamin cofactor required for methyl transfer from SAM to a peptide substrate. However, Mmp10 has little sequence homology to known methylases, suggesting this enzyme belongs to a new subclass of B12-dependent RS methylases.
Highlights
Biochemical methylation reactions are seemingly some of the most straightforward and simple of all enzyme-catalyzed reactions (1)
As reported by Radle et al (8), Mmp[10] is an radical SAM (RS) enzyme that incorporates a C-terminal domain annotated as DUF512
Class C methylases are proposed to use 5Ј-dA1⁄7 to abstract a hydrogen from the methyl group on a second SAM molecule, generating a SAM-bound methylene radical that attacks a bond in the substrate; electron and proton transfers generate a product with a methylene group in a cyclopropane ring or a methyl group containing one solvent-derived hydrogen
Summary
Biochemical methylation reactions are seemingly some of the most straightforward and simple of all enzyme-catalyzed reactions (1). The RS superfamily has evolved to catalyze diverse reactions through the addition of N- and C-terminal domains that bind substrates and/or additional cofactors that augment the basic RS chemistry (7).
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