Shelomi Matan, Heckel David G, Pauchet Yannick
Department of Entomology, Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07745 Jena, Germany.
Department of Entomology, Max Planck Institute for Chemical Ecology, Hans-Knöll-Str. 8, 07745 Jena, Germany.
Insect Biochem Mol Biol. 2016 Apr;71:1-11. doi: 10.1016/j.ibmb.2016.02.003. Epub 2016 Feb 11.
The Phasmatodea (stick insects) have multiple, endogenous, highly expressed copies of glycoside hydrolase family 9 (GH9) genes. The purpose for retaining so many was unknown. We cloned and expressed the enzymes in transfected insect cell lines, and tested the individual proteins against different plant cell wall component poly- and oligosaccharides. Nearly all isolated enzymes were active against carboxymethylcellulose, however most could also degrade glucomannan, and some also either xylan or xyloglucan. The latter two enzyme groups were each monophyletic, suggesting the evolution of these novel substrate specificities in an early ancestor of the order. Such enzymes are highly unusual for Metazoa, for which no xyloglucanases had been reported. Phasmatodea gut extracts could degrade multiple plant cell wall components fully into sugar monomers, suggesting that enzymatic breakdown of plant cell walls by the entire Phasmatodea digestome may contribute to the Phasmatodea nutritional budget. The duplication and neofunctionalization of GH9s in the ancestral Phasmatodea may have enabled them to specialize as folivores and diverge from their omnivorous ancestors. The structural changes enabling these unprecedented activities in the cellulases require further study.
竹节虫目（竹节虫）拥有多个内源性、高表达的糖苷水解酶家族9（GH9）基因拷贝。保留如此多拷贝的目的尚不清楚。我们在转染的昆虫细胞系中克隆并表达了这些酶，并针对不同的植物细胞壁成分多糖和寡糖测试了各个蛋白质。几乎所有分离出的酶都对羧甲基纤维素有活性，然而大多数酶也能降解葡甘露聚糖，有些还能降解木聚糖或木葡聚糖。后两组酶各自形成单系群，这表明这些新的底物特异性是在该目早期祖先中进化而来的。此类酶对于后生动物来说非常罕见，此前尚未有关于木葡聚糖酶的报道。竹节虫肠道提取物能够将多种植物细胞壁成分完全降解为糖单体，这表明整个竹节虫消化组对植物细胞壁的酶促分解可能有助于竹节虫的营养摄取。祖先竹节虫中GH9的复制和新功能化可能使它们能够专门以树叶为食，并与其杂食性祖先分化。使纤维素酶具有这些前所未有的活性的结构变化需要进一步研究。
