Biosynthesis of 10,12-dienoic fatty acids by a bifunctional Δ11desaturase in Spodoptera littoralis

In the biosynthetic pathway of Spodoptera littoralis sex pheromone, (E,E)-10,12-tetradecadienoic acid is produced from (Z)-11-tetradecenoic acid by desaturation and concomitant migration of the precursor double bond. With the aim of identifying the enzyme involved in this biotransformation, yeast Δelo1/Δole mutants, which are both elongase 1 and Δ9 desaturase-deficient, were transformed with the S. littoralis Δ11 desaturase gene using a Cu+2 inducible expression vector. The transformants produced a recombinant polyhistidine-tagged Δ11 desaturase that could be detected by immunoblotting from cell lysates. Lipid analysis revealed that besides producing large quantities of C11-monounsaturated fatty acids, mainly (Z)-11-hexadecenoic acid, (E,E)-10,12-tetradecadienoic acid and minor amounts of (E,Z)-10,12-hexadecadienoic acid were also produced, as well as very low quantities of another tetradecadienoate, which was tentatively identified as the (E,Z)-10,12-tetradecadienoic isomer. None of these dienes was detected with the Δ11 desaturase gene of Trichoplusia ni, which does not produce conjugated dienes as pheromone components. We conclude that the Δ11 desaturase of S. littoralis is a bifunctional enzyme with both Δ11 and Δ10,12 desaturation activities. The relationship between the substrate structure and the stereochemical outcome of the reaction is discussed.