Nitrile hydratase alpha /Thiocyanate hydrolase gamma (IPR004232)

Short name: CN_Hdrtase_a/SCN_Hdrlase_g

Overlapping homologous superfamilies

Domain relationships


Nitrile hydratases (EC: are bacterial enzymes that catalyse the hydration of nitrile compounds to the corresponding amides. They are used as biocatalysts in acrylamide production, one of the few commercial scale bioprocesses, as well as in environmental remediation for the removal of nitriles from waste streams. Nitrile hydratases are composed of two subunits, alpha and beta, and are normally active as a tetramer, alpha(2)beta(2). Nitrile hydratases contain either a non-haem iron or a non-corrinoid cobalt centre, both types sharing a highly conserved peptide sequence in the alpha subunit (CXLCSC) that provides all the residues involved in coordinating the metal ion. Each type of nitrile hydratase specifically incorporated its metal with the help of activator proteins encoded by flanking regions of the nitrile hydratase genes that are necessary for metal insertion. The Fe-containing enzyme is photo-regulated: in the dark the enzyme is inactivated due to the association of nitric oxide (NO) to the iron, while in the light the enzyme is active by photo-dissociation of NO. The NO is held in place by a claw setting formed through specific oxygen atoms in two modified cysteines and a serine residue in the active site [PMID: 9586994, PMID: 9195885]. The cobalt-containing enzyme is unaffected by NO, but was shown to undergo a similar effect with carbon monoxide [PMID: 17267045, PMID: 14717710]. Fe- and cobalt-containing enzymes also display different inhibition patterns with nitrophenols.

Thiocyanate hydrolase (SCNase) is a cobalt-containing metalloenzyme with a cysteine-sulphinic acid ligand that hydrolyses thiocyanate to carbonyl sulphide and ammonia [PMID: 16417356].

The two enzymes, nitrile hydratase and SCNase, are homologous over regions corresponding to almost the entire coding regions of the genes: the beta and alpha subunits of thiocyanate hydrolase were homologous to the amino- and carboxyl-terminal halves of the beta subunit of nitrile hydratase, and the gamma subunit of thiocyanate hydrolase was homologous to the alpha subunit of nitrile hydratase [PMID: 9573140].

This entry represents the structural domain of the alpha subunit of both iron- and cobalt-containing nitrile hydratases; the alpha subunit is a duplication of two structural repeats, each consisting of 4 layers, alpha/beta/beta/alpha [PMID: 9195885]. This structure is also found in the related protein, the gamma subunit of thiocyanate hydrolase (SCNase).

GO terms

Biological Process

GO:0006807 nitrogen compound metabolic process

Molecular Function

GO:0003824 catalytic activity
GO:0046914 transition metal ion binding

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
  • PD007559 (CN_Hdrtase_asu/SCN_Hdrlase_gsu)