Characterization and Analysis of Novel Carboxyl/Cholinesterase Genes Possessing the Thr-316 Motif in the Silkworm, Bombyx mori

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Juvenile hormone esterases (JHEs) function in juvenile hormone (JH) degradation. In the silkworm, Bombyx mori, we have characterized authentic JHE (Bmjhe) and five other carboxyl/cholinesterase (CCE) genes (Bmcce-1 to -5) with GQSAG, a motif sequence of JHE. But none of the genes appeared to function in vivo as a JHE, except for Bmjhe. Recently it was reported that the GQSAG motif might be dispensable, and that the Thr-316 residue has functional significance for JHE activity. On the basis of these findings, we identified two novel JHE candidates, Bmcce-6 and Bmcce-7, that lack GQSAG but possess Thr-316. In the CCE phylogenetic tree, BmCCE-6 was close to the lepidopteran JHE cluster, while BmCCE-7 constituted the same cluster as pheromone-degrading esterases. The developmental expression profiles were different among Bmjhe, Bmcce-6, and Bmcce-7. None of the proteins hydrolyzed JH in vitro. Our results suggest that only one CCE (BmJHE) functions as JHE in the silkworm.