Linoleate dioxygenase-cytochrome P450 (DOX-CYP) fusion enzymes are common in pathogenic fungi. The DOX domains form hydroperoxy metabolites of 18:2n-6， which can be transformed by the CYP domains to 1，2- or 1，4-diols， epoxy alcohols， or to allene oxides. We have characterized two novel allene oxide synthases (AOSs)， namely， recombinant 8R-DOX-AOS of Coccidioides immitis (causing valley fever) and 8S-DOX-AOS of Zymoseptoria tritici (causing septoria tritici blotch of wheat). The 8R-DOX-AOS oxidized 18:2n-6 sequentially to 8R-hydroperoxy-9Z，12Z-octadecadienoic acid (8R-HPODE) and to an allene oxide， 8R -epoxy-9，12Z-octadecadienoic acid， as judged from the accumulation of the α-ketol， 8S-h... More
Linoleate dioxygenase-cytochrome P450 (DOX-CYP) fusion enzymes are common in pathogenic fungi. The DOX domains form hydroperoxy metabolites of 18:2n-6， which can be transformed by the CYP domains to 1，2- or 1，4-diols， epoxy alcohols， or to allene oxides. We have characterized two novel allene oxide synthases (AOSs)， namely， recombinant 8R-DOX-AOS of Coccidioides immitis (causing valley fever) and 8S-DOX-AOS of Zymoseptoria tritici (causing septoria tritici blotch of wheat). The 8R-DOX-AOS oxidized 18:2n-6 sequentially to 8R-hydroperoxy-9Z，12Z-octadecadienoic acid (8R-HPODE) and to an allene oxide， 8R -epoxy-9，12Z-octadecadienoic acid， as judged from the accumulation of the α-ketol， 8S-hydroxy-9-oxo-12Z-octadecenoic acid. The 8S-DOX-AOS of Z. tritici transformed 18:2n-6 sequentially to 8S-HPODE and to an α-ketol， 8R-hydroxy-9-oxo-12Z-octadecenoic acid， likely formed by hydrolysis of 8S -epoxy-9，12Z-octadecadienoic acid. The 8S-DOX-AOS oxidized [8R- H]18:2n-6 to 8S-HPODE with retention of the H-label， suggesting suprafacial hydrogen abstraction and oxygenation in contrast to 8R-DOX-AOS. Both enzymes oxidized 18:1n-9 and 18:3n-3 to α-ketols， but the catalysis of the 8R- and 8S-AOS domains differed. 8R-DOX-AOS transformed 9R-HPODE to epoxy alcohols， but 8S-DOX-AOS converted 9S-HPODE to an α-ketol (9-hydroxy-10-oxo-12Z-octadecenoic acid) and epoxy alcohols in a ratio of ∼1:2. Whereas all fatty acid allene oxides described so far have a conjugated diene impinging on the epoxide， the allene oxides formed by 8-DOX-AOS are unconjugated.
