National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, Japan.
Insect Biochem Mol Biol. 2010 Feb;40(2):100-12. doi: 10.1016/j.ibmb.2009.12.015. Epub 2010 Jan 7.
We have previously cloned and characterized BmJHE, a juvenile hormone (JH)-selective esterase (JHE) that is important for JH titer regulation in the silkworm Bombyx mori. Here, we sought to determine whether multiple genes might function as JH-specific esterase in this species. We searched for putative carboxyl/cholinesterase (CCE) genes having GQSAG, a highly conserved motif in JHE, by the use of silkworm genomic database. Five novel CCE genes (Bmcce-1-5) were identified and their cDNA sequences and intron-exon structures were determined. We investigated the developmental expression patterns of these CCE genes by real-time quantitative PCR analysis and found that their expression patterns varied among developmental stages and organs. Of the proteins produced by the five genes, only BmCCE-5 had the ability to degrade JH; however, this protein might not function as a JH-specific esterase in vivo as it had a high K(m) value for JH. On the other hand, BmCCE-5 degraded general esterase substrates efficiently. Since Bmcce-5 was strongly expressed in Malpighian tubules and the gut, it might function in digestion or xenobiotic metabolism. Our results suggest that of the CCEs containing a GQSAG motif only BmJHE can function as a JH-specific degradation enzyme in the silkworm.
我们之前已经克隆并鉴定了 BmJHE，这是一种在桑蚕 Bombyx mori 中对调节保幼激素（JH）滴度很重要的 JH 选择性酯酶（JHE）。在这里，我们试图确定在该物种中是否有多个基因可能作为 JH 特异性酯酶发挥作用。我们通过使用家蚕基因组数据库，搜索具有 GQSAG 高度保守基序的假定羧基/胆碱酯酶（CCE）基因。鉴定出了五个新的 CCE 基因（Bmcce-1-5），并确定了它们的 cDNA 序列和内含子-外显子结构。我们通过实时定量 PCR 分析研究了这些 CCE 基因的发育表达模式，发现它们的表达模式在不同的发育阶段和器官中存在差异。在这五个基因产生的蛋白质中，只有 BmCCE-5 具有降解 JH 的能力；然而，由于该蛋白对 JH 的 K(m) 值较高，它可能不会在体内作为 JH 特异性酯酶发挥作用。另一方面，BmCCE-5 有效地降解了一般的酯酶底物。由于 Bmcce-5 在马氏管和肠道中强烈表达，它可能在消化或外来生物代谢中发挥作用。我们的结果表明，在含有 GQSAG 基序的 CCE 中，只有 BmJHE 可以在家蚕中作为 JH 特异性降解酶发挥作用。
