Ovothiol A is N1-methyl-4-mercaptohistidine. In the absence of S-adenosylmethione, a methyl donor, the intermediate produced is 4-mercaptohistidine. In both Erwinia tasmaniensis and Trypanosoma cruzi, a protein occurs with 5-histidylcysteine sulfoxide synthase activity, but these two enzymes and most homologs share an additional C-terminal methyltransferase domain. Thus OvoA may be a bifunctional enzyme with 5-histidylcysteine sulfoxide synthase and 4-mercaptohistidine N1-methyltranferase activity. This model describes the 5-histidylcysteine sulfoxide synthase domain, a homolog of the ergothioneine biosynthesis protein EgtB. [Biosynthesis of cofactors, prosthetic groups, and carriers, Glutathione and analogs]
Jiyao W et al.(2023). "The conserved domain database in 2023.",