Department of Biology, Washington and Lee University, USA.
Mol Biol Evol. 2013 Mar;30(3):589-601. doi: 10.1093/molbev/mss254. Epub 2012 Nov 15.
Spider silk fibers have impressive mechanical properties and are primarily composed of highly repetitive structural proteins (termed spidroins) encoded by a single gene family. Most characterized spidroin genes are incompletely known because of their extreme size (typically >9 kb) and repetitiveness, limiting understanding of the evolutionary processes that gave rise to their unusual gene architectures. The only complete spidroin genes characterized thus far form the dragline in the Western black widow, Latrodectus hesperus. Here, we describe the first complete gene sequence encoding the aciniform spidroin AcSp1, the primary component of spider prey-wrapping fibers. L. hesperus AcSp1 contains a single enormous (∼19 kb) exon. The AcSp1 repeat sequence is exceptionally conserved between two widow species (∼94% identity) and between widows and distantly related orb-weavers (∼30% identity), consistent with a history of strong purifying selection on its amino acid sequence. Furthermore, the 16 repeats (each 371-375 amino acids long) found in black widow AcSp1 are, on average, >99% identical at the nucleotide level. A combination of stabilizing selection on amino acid sequence, selection on silent sites, and intragenic recombination likely explains the extreme homogenization of AcSp1 repeats. In addition, phylogenetic analyses of spidroin paralogs support a gene duplication event occurring concomitantly with specialization of the aciniform glands and the tubuliform glands, which synthesize egg-case silk. With repeats that are dramatically different in length and amino acid composition from dragline spidroins, our L. hesperus AcSp1 expands the knowledge base for developing silk-based biomimetic technologies.
蜘蛛丝纤维具有令人印象深刻的机械性能，主要由高度重复的结构蛋白（称为蜘蛛丝蛋白）组成，这些蛋白由单一基因家族编码。大多数特征明确的蜘蛛丝蛋白基因由于其极端大小（通常>9kb）和重复性而不完全为人所知，这限制了对导致其不寻常基因结构的进化过程的理解。迄今为止，唯一特征明确的完整蜘蛛丝蛋白基因构成了西方黑寡妇（Latrodectus hesperus）的拖丝。在这里，我们描述了第一个编码aciniform 蜘蛛丝蛋白 AcSp1 的完整基因序列，该基因是蜘蛛捕食包裹纤维的主要成分。L. hesperus AcSp1 包含一个单一的巨大（约 19kb）外显子。AcSp1 重复序列在两种寡妇物种之间（约 94%的同一性）和寡妇与远缘的圆蛛之间（约 30%的同一性）非常保守，这与对其氨基酸序列的强烈净化选择相一致。此外，在黑寡妇 AcSp1 中发现的 16 个重复（每个 371-375 个氨基酸长）在核苷酸水平上平均具有>99%的同一性。对氨基酸序列的稳定选择、沉默位点的选择以及基因内重组的结合可能解释了 AcSp1 重复序列的极度同质化。此外，蜘蛛丝蛋白旁系同源物的系统发育分析支持基因复制事件与 aciniform 腺和tubuliform 腺的特化同时发生，这两种腺合成卵壳丝。我们的 L. hesperus AcSp1 具有与拖丝蜘蛛丝蛋白显著不同的长度和氨基酸组成的重复序列，扩展了开发基于丝的仿生技术的知识库。
