Homocysteine-binding domain (IPR003726)

Short name: HCY_dom

Overlapping homologous superfamilies

Domain relationships



The homocysteine (Hcy) binding domain is an ~300-residue module which is found in a set of enzymes involved in alkyl transfer to thiols:

  • Prokaryotic and eukaryotic B12-dependent methionine synthase (MetH) (EC, a large, modular protein that catalyses the transfer of a methyl group from methyltetrahydrofolate (CH3-H4folate) to Hcy to form methionine, using cobalamin as an intermediate methyl carrier.
  • Mammalian betaine-homocysteine S-methyltransferase (BHMT) (EC It catalyzes the transfer of a methyl group from glycine betaine to Hcy, forming methionine and dimethylglycine.
  • Plant selenocysteine methyltransferase (EC 2.1.1.-).
  • Plant and fungal AdoMet homocysteine S-methyltransferases (EC

The Hcy-binding domain utilises a Zn(Cys)3 cluster to bind and activate Hcy. It has been shown to form a (beta/alpha)8 barrel. The Hcy binding domain barrel is distorted to form the metal- and substrate-binding sites. To accommodate the substrate, strands 1 and 2 of the barrel are loosely joined by nonclassic hydrogen bonds; to accommodate the metal, strands 6 and 8 are drawn together and strand 7 is extruded from the end of the barrel. The cysteines ligating the catalytic zinc atom are located at the C-terminal ends of strands 6 and 8 [PMID: 12220488, PMID: 14752199].

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles