Ipsdienol dehydrogenase (IDOLDH): A novel oxidoreductase important for Ips pini pheromone production

Ipsdienone (2-methyl-6-methylene-2,7-octadien-4-one) is an important intermediate in the biosynthesis of pheromonal ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol) and ipsenol (2-methyl-6-methylene-7-octen-4-ol) in male pine engraver beetles, Ips pini (Say). A novel ipsdienol dehydrogenase (IDOLDH) with a pheromone-biosynthetic gene expression pattern was cloned, expressed, functionally characterized, and its cellular localization analyzed. The cDNA has a 762 nt ORF encoding a 253 amino acid predicted translation product of 28 kDa and pI 5.8. The protein has conserved motifs of the Cp2 subfamily of “classical” short-chain dehydrogenases. Transcript levels were highest in pheromone producing tissue: the anterior midgut of fed males. The protein was detected only in male midguts and localized in the cytosolic fraction of midgut cells. Recombinant IDOLDH was produced in Sf9 cells using a baculovirus expression system. Enzyme assays of protein preparations showed IDOLDH used both NAD⁺ and NADP⁺ as coenzymes with specific activities in the nanomole range. Enzyme assays and GC/MS analysis showed that IDOLDH catalyzed the oxidation of racemic ipsdienol and (4R)-(−)-ipsdienol to form ipsdienone, while (4S)-(+)-ipsdienol was not a substrate. These data strongly implicate IDOLDH as an enzyme involved in terminal pheromone-biosynthetic steps, likely functioning to “tune” ipsdienol enantiomeric ratios.

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► The ratio of (−)-:(+)-ipsdienol is important for Ips spp. pheromone biochemistry.
► Ipsdienol dehydrogenase (IDOLDH) stereo-selectively oxidizes (−)-ipsdienol but not (+)-ipsdienol to ipsdienone.
► IDOLDH mRNA and enzyme activities are consistent with a role in pheromone metabolism.
► Other oxidoreductases are likely involved in adjusting Ips spp. pheromone composition.