Cloning and functional expression of a cDNA encoding a pheromone gland-specific acyl-CoA Δ-desaturase of the cabbage looper moth, Trichoplusia ni

Desaturation of coenzyme-A esters of saturated fatty acids is a common feature of sex pheromone biosynthetic pathways in the Lepidoptera. The enzymes that catalyze this step share several biochemical properties with the ubiquitous acyl-CoA Δ-desaturases of animals and fungi, suggesting a common ancestral origin. Unlike metabolic acyl-CoA Δ-desaturases, pheromone desaturases have evolved unusual regio- and stereoselective activities that contribute to the remarkable diversity of chemical structures used as pheromones in this large taxonomic group. In this report, we describe the isolation of a cDNA encoding a pheromone gland desaturase from the cabbage looper moth, Trichoplusia ni, a species in which all unsaturated pheromone products are produced via a ΔZ-desaturation mechanism. The largest ORF of the ≈1,250-bp cDNA encodes a 349-aa apoprotein (PDesat-Tn ΔZ) with a predicted molecular mass of 40,240 Da. Its hydrophobicity profile is similar overall to those of rat and yeast Δ-desaturases, suggesting conserved transmembrane topology. A 182-aa core domain delimited by conserved histidine-rich motifs implicated in iron-binding and catalysis has 72 and 58% similarity (including conservative substitutions) to acyl-CoA ΔZ-desaturases of rat and yeast, respectively. Northern blot analysis revealed an ≈1,250-nt PDesat-Tn ΔZ mRNA that is consistent with the spatial and temporal distribution of Δ-desaturase enzyme activity. Genetic transformation of a desaturase-deficient strain of the yeast Saccharomyces cerevisiae with an expression plasmid encoding PDesat-Tn ΔZ resulted in complementation of the strain's fatty acid auxotrophy and the production of ΔZ-unsaturated fatty acids.