Department of Biology, University of California, Riverside, CA 92521, USA.
J Mol Evol. 2010 May;70(5):519-29. doi: 10.1007/s00239-010-9349-8. Epub 2010 May 11.
Silk production has independently evolved in numerous arthropod lineages, such as Lepidoptera, the moths and butterflies. Lepidopteran larvae (caterpillars) synthesize silk proteins in modified salivary glands and spin silk fibers into protective tunnels, escape lines, and pupation cocoons. Molecular sequence data for these proteins are necessary to determine critical features of their function and evolution. To this end, we constructed an expression library from the silk glands of the ghost moth, Hepialus californicus, and characterized light chain fibroin and heavy chain fibroin gene transcripts. The predicted H. californicus silk fibroins share many elements with other lepidopteran and trichopteran fibroins, such as conserved placements of cysteine, aromatic, and polar amino acid residues. Further comparative analyses were performed to determine site-specific signatures of selection and to assess whether fibroin genes are informative as phylogenetic markers. We found that purifying selection has constrained mutation within the fibroins and that light chain fibroin is a promising molecular marker. Thus, by characterizing the H. californicus fibroins, we identified key functional amino acids and gained insight into the evolutionary processes that have shaped these adaptive molecules.
丝的生产在许多节肢动物谱系中独立进化，例如鳞翅目，蛾和蝴蝶。鳞翅目幼虫（毛毛虫）在改良的唾液腺中合成丝蛋白，并将丝纤维纺成保护性隧道、逃逸线和蛹化茧。这些蛋白质的分子序列数据对于确定其功能和进化的关键特征是必要的。为此，我们从幽灵蛾 Hepialus californicus 的丝腺中构建了一个表达文库，并对轻链丝素和重链丝素基因转录本进行了表征。预测的 H. californicus 丝纤维与其他鳞翅目和毛翅目丝纤维有许多共同之处，例如半胱氨酸、芳香族和极性氨基酸残基的保守位置。进一步的比较分析是为了确定选择的特定位置特征，并评估丝素基因是否作为系统发育标记具有信息性。我们发现，在丝素纤维中，纯化选择限制了突变，并且轻链丝素是一种很有前途的分子标记。因此，通过表征 H. californicus 的丝纤维，我们确定了关键的功能氨基酸，并深入了解了塑造这些适应性分子的进化过程。
