Biosynthesis of 10,12-dienoic fatty acids by a bifunctional Δ 11desaturase in Spodoptera littoralis

Abstract

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 Δ elo1/Δ ole mutants, which are both elongase 1 and Δ 9 desaturase-deficient, were transformed with the S. littoralis Δ 11 desaturase gene using a Cu +2 inducible expression vector. The transformants produced a recombinant polyhistidine-tagged Δ 11 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 Δ 11 desaturase gene of Trichoplusia ni, which does not produce conjugated dienes as pheromone components. We conclude that the Δ 11 desaturase of S. littoralis is a bifunctional enzyme with both Δ 11 and Δ 10,12 desaturation activities. The relationship between the substrate structure and the stereochemical outcome of the reaction is discussed.