CHARACTERIZATION OF HOVI-MEH1, A MICROSOMAL EPOXIDE HYDROLASE FROM THE GLASSY-WINGED SHARPSHOOTER Homalodisca vitripennis
Epoxide hydrolase (EH) is an enzyme in the alpha/beta-hydrolase fold superfamily that uses a water molecule to transform an epoxide to its corresponding diol. In insects, EHs metabolize among other things critical developmental hormones called juvenile hormones (JHs). EHs also play roles in the detoxification of toxic compounds that are found in the insect's diet or environment. In this study, a full-length cDNA encoding an epoxide hydrolase, Hovi-mEH1, was obtained from the xylem-feeding insect Homalodisca vitripennis. H. vitripennis, commonly known as the glassy-winged sharpshooter, is an economically important vector of plant pathogenic bacteria such as Xylella fastidiosa. Hovi-mEH1 hydrolyzed the general EH substrates cis-stilbene oxide and trans-diphenylpropene oxide with specific activities of 47.5 +/- 6.2 and 1.3 +/- 0.5 nmol of diol formed min(-1) mg(-1), respectively. Hovi-mEH1 metabolized JH III with a V-max of 29.3 +/- 1.6 nmol min(-1) mg(-1), k(cat) of 0.03 s(-1), and K-M of 13.8 +/- 2.0 mu M. These V-max and k(cat) values are similar to those of known JH metabolizing EHs from lepidopteran and coleopteran insects. Hovi-mEH1 showed 99.1% identity to one of three predicted EH-encoding sequences that were identified in the transcriptome of H. vitripennis. Of these three sequences only Hovi-mEH1 clustered with known JH metabolizing EHs. On the basis of biochemical, phylogenetic, and transcriptome analyses, we hypothesize that Hovi-mEH1 is a biologically relevant JH-metabolizing enzyme in H. vitripennis. (C) 2013 Wiley Periodicals, Inc.