Structure determination and analysis of acyl-CoA oxidase (ACX1) from tomato

The flavoenzyme acyl-CoA oxidase (ACX) catalyzes the first committed step in beta-oxidation and is required for the biosynthesis of jasmonic acid, a signaling molecule involved in plant defense. Recently, a mutant in tomato was identified that is deficient in jasmonic acid production and compromised in its wound response. This results from a single point mutation in acx1, which causes the conserved residue Thr138 to be substituted by isoleucine. To understand the structural basis for this mutation, the crystal structure of LeACX1 was determined to 2.74 Angstrom resolution by molecular replacement. Unexpectedly, an unusual packing arrangement was observed in which three monomers of LeACX1 are present in the asymmetric unit. Although the tertiary structure of LeACX1 is essentially similar to the previously determined structures of ACX enzymes, the packing within the unit cells is distinctly different.