IUBMB Enzyme Nomenclature


Accepted name: oxazoline synthase

Reaction: (1) ATP + a [protein]-(L-amino acyl-L-serine) = ADP + phosphate + a [protein]-(S,S)-2-(C-substituted-aminomethyl)-4-acyl-2-oxazoline
(2) ATP + a [protein]-(L-amino acyl-L-threonine) = ADP + phosphate + a [protein]-(S,S)-2-(C-substituted-aminomethyl)-4-acyl-5-methyl-2-oxazoline
(3) ATP + a [protein]-(L-amino acyl-L-cysteine) = ADP + phosphate + a [protein]-(1S,4R)-2-(C-substituted-aminomethyl)-4-acyl-2-thiazoline

Other name(s): cyanobactin heterocyclase; cyanobactin cyclodehydratase; patD (gene name); balhD (gene name); micD (gene name)

Systematic name: [peptide]-(L-amino acyl-L-serine) cyclodehydratase (2-oxazoline-forming)

Comments: Requires Mg2+. The enzyme, which participates in the biosynthesis of ribosomal peptide natural products (RiPPs), converts L-cysteine, L-serine and L-threonine residues to thiazoline, oxazoline, and methyloxazoline rings, respectively. The enzyme requires two domains - a cyclodehydratase domain, known as a YcaO domain, and a substrate recognition domain (RRE domain) that controls the regiospecificity of the enzyme. The RRE domain can either be fused to the YcaO domain or occur as a separate protein; however both domains are required for activity. The enzyme can process multiple residues within the same substrate peptide, and all enzymes characterized so far follow a defined order, starting with the L-cysteine closest to the C-terminus. The reaction involves phosphorylation of the preceding ribosomal peptide backbone amide bond, forming ADP and a phosphorylated intermediate, followed by release of the phosphate group. In some cases the enzyme catalyses a side reaction in which the phosphorylated intermediate reacts with ADP to form AMP and diphosphate.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc CAS registry number:


1. McIntosh, J.A., Donia, M.S. and Schmidt, E.W. Insights into heterocyclization from two highly similar enzymes. J. Am. Chem. Soc. 132 (2010) 4089-4091. [PMID: 20210311]

2. Melby, J.O., Dunbar, K.L., Trinh, N.Q. and Mitchell, D.A. Selectivity, directionality, and promiscuity in peptide processing from a Bacillus sp. Al Hakam cyclodehydratase. J. Am. Chem. Soc. 134 (2012) 5309-5316. [PMID: 22401305]

3. Ge, Y., Czekster, C.M., Miller, O.K., Botting, C.H., Schwarz-Linek, U. and Naismith, J.H. Insights into the mechanism of the cyanobactin heterocyclase enzyme. Biochemistry 58 (2019) 2125-2132. [PMID: 30912640]

[EC created 2020]

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