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105  structures 777  species 3  interactions 1016  sequences 8  architectures

Family: NHase_alpha (PF02979)

Summary: Nitrile hydratase, alpha chain

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Nitrile hydratase Edit Wikipedia article

nitrile hydratase
EC number
CAS number 82391-37-5
IntEnz IntEnz view
ExPASy NiceZyme view
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum
Gene Ontology AmiGO / EGO

In enzymology, nitrile hydratases (NHases; EC are mononuclear iron or non-corrinoid cobalt enzymes that catalyse the hydration of diverse nitriles to their corresponding amides

R-C≡N + H2O → R-C(O)NH2

Metal cofactor

In biochemistry, cobalt is in general found in a corrin ring, such as in vitamin B12. Nitrile hydratase is one of the rare enzyme types that use cobalt in a non-corrinoid manner. The mechanism by which the cobalt is transported to NHase without causing toxicity is unclear, although a cobalt permease has been identified, which transports cobalt across the cell membrane. The identity of the metal in the active site of a nitrile hydratase can be predicted by analysis of the sequence data of the alpha subunit in the region where the metal is bound. The presence of the amino acid sequence VCTLC indicates a Co-centred NHase and the presence of VCSLC indicates Fe-centred NHase.

Metabolic pathway

Nitrile hydratase and amidase are two hydrating and hydrolytic enzymes responsible for the sequential metabolism of nitriles in bacteria that are capable of utilising nitriles as their sole source of nitrogen and carbon, and in concert act as an alternative to nitrilase activity, which performs nitrile hydrolysis without formation of an intermediate primary amide. A sequence in genome of the choanoflagellate Monosiga brevicollis was suggested to encode for a nitrile hydratase.[1] The M. brevicollis gene consisted of both the alpha and beta subunits fused into a single gene. Similar nitrile hydratase genes consisting of a fusion of the beta and alpha subunits have since been identified in several eukaryotic supergroups, suggesting that such nitrile hydratases were present in the last common ancestor of all eukaryotes.[2]

Industrial applications

NHases have been efficiently used for the industrial production of acrylamide from acrylonitrile[3] on a scale of 600 000 tons per annum,[4] and for removal of nitriles from wastewater. Photosensitive NHases intrinsically possess nitric oxide (NO) bound to the iron centre, and its photodissociation activates the enzyme. Nicotinamide is produced industrially[3] by the hydrolysis of 3-cyanopyridine catalysed by the nitrile hydratase from Rhodococcus rhodochrous J1,[5][6] producing 3500 tons per annum of nicotinamide for use in animal feed.[4]


Structure of nitrile hydratase.[7]

NHases are composed of two types of subunits, α and β, which are not related in amino acid sequence. NHases exist as αβ dimers or α2β2 tetramers and bind one metal atom per αβ unit. The 3-D structures of a number of NHases have been determined. The α subunit consists of a long extended N-terminal "arm", containing two α-helices, and a C-terminal domain with an unusual four-layered structure (α-β-β-α). The β subunit consists of a long N-terminal loop that wraps around the α subunit, a helical domain that packs with N-terminal domain of the α subunit, and a C-terminal domain consisting of a β-roll and one short helix.

Nitrile hydratase, alpha chain
Symbol NHase_alpha
Pfam PF02979
InterPro IPR004232
SCOP 2ahj
Nitrile hydratase beta subunit
Symbol NHase_beta
Pfam PF02211
InterPro IPR003168
SCOP 2ahj


An assembly pathway for nitrile hydratase was first proposed when gel filtration experiments found that the complex exists in both αβ and α2β2 forms.[8] In vitro experiments using mass spectrometry further revealed that the α and β subunits first assemble to form the αβ dimer. The dimers can then subsequently interact to form a tetramer.[9]


The metal centre is located in the central cavity at the interface between two subunits. All protein ligands to the metal atom are provided by the α subunit. The protein ligands to the iron are the sidechains of the three cysteine (Cys) residues and two mainchain amide nitrogens. The metal ion is octahedrally coordinated, with the protein ligands at the five vertices of an octahedron. The sixth position, accessible to the active site cleft, is occupied either by NO or by a solvent-exchangeable ligand (hydroxide or water). The two Cys residues coordinated to the metal are post-translationally modified to Cys-sulfinic (Cys-SO2H) and -sulfenic (Cys-SOH) acids.

Quantum chemical studies predicted that the Cys-SOH residue might play a role as either a base (activating a nucleophilic water molecule)[10] or as a nucleophile.[11] Subsequently, the functional role of the SOH center as nucleophile has obtained experimental support.[12]


  1. ^ Foerstner KU, Doerks T, Muller J, Raes J, Bork P (2008). Hannenhalli, Sridhar, ed. "A nitrile hydratase in the eukaryote Monosiga brevicollis". PLoS ONE. 3 (12): e3976. PMC 2603476Freely accessible. PMID 19096720. doi:10.1371/journal.pone.0003976. 
  2. ^ Marron AO, Akam M, Walker G (2012). Stiller, John, ed. "Nitrile Hydratase Genes Are Present in Multiple Eukaryotic Supergroups". PLoS ONE. 7 (4): e32867. PMC 3323583Freely accessible. PMID 22505998. doi:10.1371/journal.pone.0032867. 
  3. ^ a b Schmidberger, J. W.; Hepworth, L. J.; Green, A. P.; Flitsch, S. L. (2015). "Enzymatic Synthesis of Amides". In Faber, Kurt; Fessner, Wolf-Dieter; Turner, Nicholas J. Biocatalysis in Organic Synthesis 1. Science of Synthesis. Georg Thieme Verlag. pp. 329–372. 
  4. ^ a b Asano, Y. (2015). "Hydrolysis of Nitriles to Amides". In Faber, Kurt; Fessner, Wolf-Dieter; Turner, Nicholas J. Biocatalysis in Organic Synthesis 1. Science of Synthesis. Georg Thieme Verlag. pp. 255–276. 
  5. ^ Nagasawa, Toru; Mathew, Caluwadewa Deepal; Mauger, Jacques; Yamada, Hideaki (1988). "Nitrile Hydratase-Catalyzed Production of Nicotinamide from 3-Cyanopyridine in Rhodococcus rhodochrous J1" (PDF). Appl. Environ. Microbiol. 54 (7): 1766–1769. 
  6. ^ Ulber, Roland; Sell, Dieter, eds. (2007). "Building Blocks". White Biotechnology. Advances in Biochemical Engineering / Biotechnology. 105. Springer Science & Business Media. pp. 133–173. ISBN 9783540456957. doi:10.1007/10_033. 
  7. ^ Nagashima S, Nakasako M, Dohmae N, et al. (May 1998). "Novel non-heme iron center of nitrile hydratase with a claw setting of oxygen atoms". Nat. Struct. Biol. 5 (5): 347–51. PMID 9586994. doi:10.1038/nsb0598-347. 
  8. ^ Payne, MS; Wu, S; Fallon, RD; Tudor, G; Stieglitz, B; Turner, IM; Nelson, MJ (May 1997). "A stereoselective cobalt-containing nitrile hydratase". Biochemistry. 36 (18): 5447–54. PMID 9154927. doi:10.1021/bi962794t. 
  9. ^ Marsh JA, Hernández H, Hall Z, Ahnert SE, Perica T, Robinson CV, Teichmann SA (Apr 2013). "Protein complexes are under evolutionary selection to assemble via ordered pathways". Cell. 153 (2): 461–470. PMC 4009401Freely accessible. PMID 23582331. doi:10.1016/j.cell.2013.02.044. 
  10. ^ Hopmann, KH; Guo JD, Himo F (2007). "Theoretical Investigation of the First-Shell Mechanism of Nitrile Hydratase". Inorg. Chem. 46 (12): 4850–4856. doi:10.1021/ic061894c. 
  11. ^ Hopmann, KH; Himo F (March 2008). "Theoretical Investigation of the Second-Shell Mechanism of Nitrile Hydratase". European Journal of Inorganic Chemistry. 2008 (9): 1406–1412. doi:10.1002/ejic.200701137. 
  12. ^ Salette, M; Wu R, Sanishvili R, Liu D, Holz RC (2014). "The Active Site Sulfenic Acid Ligand in Nitrile Hydratases can Function as a Nucleophile". JACS. 136: 1186–1189. doi:10.1021/ja410462j. 

Further reading

  • Prasad, S; Bhalla, TC (May 2010). "Nitrile hydratases (NHases): At the interface of academia and industry .". Biotechnology Advances. 28 (6): 725–41. PMID 20685247. doi:10.1016/j.biotechadv.2010.05.020. 
  • Rzeznicka, K; Schätzle, S; Böttcher, D; Klein, J; Bornscheuer, UT (Aug 2009). "Cloning and functional expression of a nitrile hydratase (NHase) from Rhodococcus equi TG328-2 in Escherichia coli, its purification and biochemical characterisation.". Appl Microbiol Biotechnol. 85 (5): 1417–25. PMID 19662400. doi:10.1007/s00253-009-2153-y. 
  • Song, L; Wang, M; Yang, X; Qian, S (Jun 2007). "Purification and characterization of the enantioselective nitrile hydratase from Rhodococcus sp. AJ270.". Biotechnol J. 2 (6): 717–24. PMID 17330219. doi:10.1002/biot.200600215. 
  • Miyanaga, A; Fushinobu, S; Ito, K; Shoun, H; Wakagi, T (Jan 2004). "Mutational and structural analysis of cobalt-containing nitrile hydratase on substrate and metal binding.". Eur J Biochem. 271 (2): 429–38. PMID 14717710. doi:10.1046/j.1432-1033.2003.03943.x. 
  • Hann, EC; Eisenberg, A; Fager, SK; Perkins, NE; Gallagher, FG; Cooper, SM; Gavagan, JE; Stieglitz, B; Hennessey, SM; DiCosimo, R (October 1999). "5-Cyanovaleramide production using immobilized Pseudomonas chlororaphis B23.". Bioorg Med Chem. 7 (10): 2239–45. PMID 10579532. doi:10.1016/S0968-0896(99)00157-1. 

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Literature references

  1. Nagashima S, Nakasako M, Dohmae N, Tsujimura M, Takio K, Odaka M, Yohda M, Kamiya N, Endo I; , Nat Struct Biol 1998;5:347-351.: Novel non-heme iron center of nitrile hydratase with a claw setting of oxygen atoms. PUBMED:9586994 EPMC:9586994

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR004232

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 [PUBMED:9586994, PUBMED:9195885]. The cobalt-containing enzyme is unaffected by NO, but was shown to undergo a similar effect with carbon monoxide [PUBMED:17267045, PUBMED: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 [PUBMED: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 [PUBMED: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 [PUBMED:9195885]. This structure is also found in the related protein, the gamma subunit of thiocyanate hydrolase (SCNase).

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Seed source: Structural domain
Previous IDs: none
Type: Domain
Sequence Ontology: SO:0000417
Author: Griffiths-Jones SR
Number in seed: 43
Number in full: 1016
Average length of the domain: 164.10 aa
Average identity of full alignment: 45 %
Average coverage of the sequence by the domain: 83.99 %

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build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 45638612 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 27.2 27.2
Trusted cut-off 27.4 27.3
Noise cut-off 27.1 27.0
Model length: 184
Family (HMM) version: 16
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NHase_alpha NHase_beta NHase_beta


For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the NHase_alpha domain has been found. There are 105 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein sequence.

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