A flavoprotein (FAD). The enzyme, characterized from the bacterium Streptosporangium sibiricum, is involved in the biosynthesis of the antitumor antibiotic sibiromycin. The enzyme is not active with free 3-hydroxy-4-methylanthranilate.
biosynthesis of the antitumor antibiotic sibiromycin. Starting from 3-hydroxykynurenine, the SAM-dependent methyltransferase SibL converts the substrate to its 4-methyl derivative, followed by hydrolysis through the action of the PLP-dependent kynureninase SibQ, leading to 3-hydroxy-4-methylanthranilic acid formation. Subsequently the nonribosomal peptide synthetase SibE activates 3-hydroxy-4-methylanthranilic acid and tethers it to its thiolation domain, where it is hydroxylated at the C5 position by the FAD/NADH-dependent hydroxylase SibG yielding the fully substituted anthranilate moiety found in sibiromycin