The biosynthesis of 3-amino-5-hydroxybenzoic acid (AHBA), the precursor of mC7N units in ansamycin and mitomycin antibiotics: a review

The aminoshikimate pathway of formation of 3-amino-5-hydroxybenzoic acid (AHBA), the precursor of ansamycin and Other Antibiotics is reviewed. In this biosynthesis, genes for kanosamine formation have been recruited from Other genomes, to provide a nitrogenous precursor. Kanosamine is then phosphorylated and converted by common cellular Enzymes into 1-deoxy-1-imino-erythrose 4-phosphate, the substrate for the formation of aminoDAHP. This is converted via 5-deoxy-5-aminodehydroquinic acid and 5-deoxy-5-aminodehydroshikimic acid into AHBA. Remarkably, the pyridoxal phosphate enzyme AHBA synthase seems to have two catalytic functions: As a homodimer, it catalyzes the last reaction in the pathway, the aromatization of 5-deoxy-5-aminodehydroshikimic acid, and at the beginning of the pathway in a complex with the oxidoreductase RifL it catalyzes the transamination of UDP-3-keto-D-glucose. The AHBA synthase gene also serves as a useful tool in the genetic screening for new ansamycins and Other AHBA-derived natural products.