Regiospecificity of a novel bacterial lipoxygenase from Myxococcus xanthus for polyunsaturated fatty acids.

Lipoxygenase (LOX) is the key enzyme involved in the synthesis of oxylipins as signaling compounds that are important for cell growth and development, inflammation, and pathogenesis in various organisms. The regiospecificity of LOX from Myxococcus xanthus, a gram-negative bacterium, was investigated. The enzyme catalyzed oxygenation at the n-9 position in C20 and C22 polyunsaturated fatty acids (PUFAs) to form 12S- and 14S-hydroxy fatty acids (HFAs), respectively, and oxygenation at the n-6 position in C18 PUFAs to form 13-HFAs. The 12S-form products of C20 and C22 PUFAs by M. xanthus LOX is the first report of bacterial LOXs. The residues involved in regiospecificity were determined to be Thr397, Ala461, and Ile664 by analyzing amino acid alignment and a homology model based on human arachidonate 15-LOX with a sequence identity of 25%. Among these variants, the regiospecificity of the T397Y variant for C20 and C22 PUFAs was changed. This may be because of the reduced size of the substrate-binding pocket by substitution of the smaller Thr to the larger Tyr residue. The T397Y variant catalyzed oxygenation at the n-6 position in C20 and C22 PUFAs to form 15- and 17-hydroperoxy fatty acids, respectively. However, the oxygenation position of T397Y for C18 PUFAs was not changed. The discovery of bacterial LOX with novel regiospecificity will facilitate the biosynthesis of regiospecific‑oxygenated signaling compounds.