(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
Substrate
ATP [CPD:C00002];
[protein]-(L-amino acyl-L-serine);
[protein]-(L-amino acyl-L-threonine);
[protein]-(L-amino acyl-L-cysteine)
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.