The carbon-nitrogen hydrolase domain is an around 265-residue domain found in numerous enzymes involved in the reduction of organic nitrogen compounds and ammonia production. Based on their sequence similarity and on the reactions they catalyze, these enzymes can be classified into functionally distinct groups including [1,2]:

• Nitrilases (EC 3.5.5.1), which cleave various nitriles into the corresponding acids and ammonia (see <PDOC00712>).
• Cyanide hydratase (EC 4.2.1.66) of pathogenic fungi, which detoxifies HCN that is released by their hosts, cyanogenic plants, after injury (see <PDOC00712>).
• Aliphatic amidases (EC 3.5.1.4), which enable prokaryotes to use acetamides as both carbon and nitrogen source.
• β-alanine synthase (N-carbamoyl-β-alanine amino hydrolase) (EC 3.5.1.6), which catalyses the last step of pyrimidine catabolism.
• AdgA (for ammonia-dependent growth) from Rhodobacter species (EC 6.3.5.1). It appears to be essential for using various amino acids as nitrogen sources.
• Biotinidase (EC 3.5.1.12), which catalyzes the hydrolysis of biocytin to biotin and lysine.
• Pantetheinase (EC 3.5.1.92) (Pantetheine hydrolase) (Vanin), which hydrolyzes specifically one of the carboamide linkages in D-pantetheine, thus recycling pantothenic acid (vitamin B5) and releasing cysteamine.
• Apolipoprotein N-acyltransferase (EC 2.3.1.-) (gene lnt), a bacterial enzyme that transfers the fatty acyl group on membrane lipoproteins.

The carbon-nitrogen hydrolase domain can be found alone or associated with other domains, such as the NAD synthase domain, the HIT histidine triad (see <PDOC00694>), the acetyltransferase domain or the glycosyltransferase domain.

The carbon-nitrogen hydrolase domain is characterized by several conserved motifs, one of which contains a cysteines that is part of the catalytic site in nitrilases. Another highly conserved motif includes a glutamic acid that might also be involved in catalysis [1].

The profile we developed covers the entire carbon-nitrogen hydrolase domain.