Characterization of Aziridine-Forming α-Ketoglutarate-Dependent Oxygenase in l-Isovaline Biosynthesis.

l-Isovaline biosynthesis by TqaLFM- ti from Tolypocladium inflatum was demonstrated in vitro . The biochemical analysis of the α-ketoglutarate-dependent oxygenase TqaL- ti revealed that it produces (2 S ,3 S )-3-ethyl-3-methylaziridine-2-carboxylic acid from l-isoleucine, thus exhibiting a stereoselectivity different from those of the reported homologues. Remarkably, a single mutation on I295 in TqaL- ti completely exchanged its stereoselectivity to produce the C-3 stereoisomer. TqaFM- ti generates d-isovaline from (2 S ,3 R )-aziridine-2-carboxylic acid, suggesting that the stereochemistry of the TqaL product defines that of isovaline.