The plant Diaminopelargonic acid aminotransferase uses spermidine as its amino donor

Biotin is an essential vitamin that is only synthesised in microorganisms, plants and fungi, so the biosynthetic pathway is of interest for antibacterial and herbicide discovery. Plants contain a single, bifunctional enzyme that catalyses two sequential steps in biotin biosynthesis, dethiobiotin synthetase-diaminopelargonic acid aminotransferase (herein referred to as BioDA). Diaminopelargonic acid aminotransferase (BioA) catalyses the pyridoxal phosphate-dependent transamination of 7-keto-8-aminopelargonic acid to produce 7,8-diaminopelargonic acid, while dethiobiotin synthetase (BioD) catalyses the subsequent step to produce dethiobiotin. In contrast to plants, in bacteria, these activities are catalysed by two separate enzymes, BioA and BioD. Most bacterial BioA enzymes use an unusual amino donor, S-adenosyl methionine, while other BioA enzymes use lysine as the amino donor. We show that the plant BioA uses spermidine as the amino donor. Spermidine binding and aminotransferase activity is stimulated by bicarbonate by an interaction with Arg 797 that is assumed to be a carbamate derivative of spermidine. We confirm a previous observation that cadaverine is a weak inhibitor of BioA, indicating that cadaverine can modulate biotin biosynthesis.