Larvae of
Tyria jacobaeae
feed solely upon the pyrrolizidine alkaloid-containing plant
Senecio jacobaea
. Ingested pyrrolizidine alkaloids (PAs), which are toxic to unspecialized insects and vertebrates, are efficiently
N
-oxidized in the hemolymph of
T. jacobaeae
by senecionine
N
-oxygenase (SNO), a flavin-dependent monooxygenase (FMO) with a high substrate specificity for PAs. Peptide microsequences obtained from purified
T. jacobaeae
SNO were used to clone the corresponding cDNA, which was expressed in active form in
Escherichia coli
.
T. jacobaeae
SNO possesses a signal peptide characteristic of extracellular proteins, and it belongs to a large family of mainly FMO-like sequences of mostly unknown function, including two predicted
Drosophila melanogaster
gene products. The data indicate that the gene for
T. jacobaeae
SNO, highly specific for toxic pyrrolizidine alkaloids, was recruited from a preexisting insect-specific FMO gene family of hitherto unknown function. The enzyme allows the larvae to feed on PA-containing plants and to accumulate predation-deterrent PAs in the hemolymph.
雅科草蛾(Tyria jacobaeae)的幼虫仅以含有吡咯啉生物碱的植物雅科草(Senecio jacobaea)为食。摄入的吡咯啉生物碱(PAs)对于非特化昆虫和脊椎动物有毒,但在雅科草蛾的血淋巴中,经由毒菊碱N-氧化酶(SNO)高效地进行N-氧化,这是一种具有高度对PAs底物特异性的黄酮依赖性单加氧酶(FMO)。从纯化的雅科草蛾SNO中获得的肽微序列被用于克隆相应的cDNA,该cDNA在大肠杆菌(Escherichia coli)中以活性形式表达。雅科草蛾SNO具有外泌蛋白特征的信号肽,并且属于一个大家族,主要是大多数未知功能的FMO样序列,包括两个预测的果蝇(Drosophila melanogaster)基因产物。数据表明,高度特异于有毒吡咯啉生物碱的雅科草蛾SNO基因,是从一个迄今未知功能的昆虫特异性FMO基因家族中招募而来的。该酶使幼虫能够以含有PA的植物为食,并在血淋巴中积累捕食威慑PAs。