Marcu O, Locke M
Department of Zoology, University of Western Ontario, London, Canada.
Insect Biochem Mol Biol. 1998 Sep;28(9):659-69. doi: 10.1016/s0965-1748(98)00048-4.
A 22 kDa peptide was purified from prepupal cuticles of 5th instar Calpodes ethlius caterpillars. It was absent earlier in the stadium and from the egg and adult, i.e. it is related to cuticle turnover rather than cuticle structure. It was present at larval and metamorphic moults, showing that it is related to moulting not just metamorphosis. The cDNA corresponding to the 22 kDa peptide was isolated by antibody screening of an epidermal cDNA expression library. Hybridization to Calpodes genomic DNA showed that the gene was present as a single copy. The deduced amino acid sequence is not like any of the sequences of cuticular structural proteins that have been published, but has a 47 amino acid sequence similar to bacteriophage T7 N-acetylmuramoyl-L-alanine amidase (34% identical, 51% similar). The amino acid sequence, the timing of expression in development, and the similarity between the substrate of the bacteriophage amidase and components of insect cuticle, all suggest that the 22 kDa protein may have a role in cleaving chitin-peptide bonds as a prerequisite for digestion of the cuticle by chitinases and proteases.
从五龄埃氏角纹夜蛾幼虫的蛹前期表皮中纯化出一种22 kDa的肽。在该龄期早期以及卵和成虫阶段均未发现这种肽，也就是说，它与表皮更新有关，而非表皮结构。它在幼虫蜕皮和变态蜕皮时均有出现，表明它不仅与变态有关，还与蜕皮有关。通过对表皮cDNA表达文库进行抗体筛选，分离出了与22 kDa肽对应的cDNA。与埃氏角纹夜蛾基因组DNA杂交显示该基因以单拷贝形式存在。推导的氨基酸序列与已发表的任何表皮结构蛋白序列均不相同，但有一段47个氨基酸的序列与噬菌体T7 N - 乙酰胞壁酰 - L - 丙氨酸酰胺酶相似（同一性为34%，相似性为51%）。氨基酸序列、在发育过程中的表达时间以及噬菌体酰胺酶底物与昆虫表皮成分之间的相似性，均表明22 kDa蛋白可能在切割几丁质 - 肽键方面发挥作用，这是几丁质酶和蛋白酶消化表皮的前提条件。
