Vienneau-Hathaway Jannelle M, Brassfield Elizabeth R, Lane Amanda Kelly, Collin Matthew A, Correa-Garhwal Sandra M, Clarke Thomas H, Schwager Evelyn E, Garb Jessica E, Hayashi Cheryl Y, Ayoub Nadia A
Department of Biology, Washington and Lee University, Lexington, VA, USA.
Department of Biology, University of California, Riverside, CA, USA.
BMC Evol Biol. 2017 Mar 14;17(1):78. doi: 10.1186/s12862-017-0927-x.
Orb-web weaving spiders and their relatives use multiple types of task-specific silks. The majority of spider silk studies have focused on the ultra-tough dragline silk synthesized in major ampullate glands, but other silk types have impressive material properties. For instance, minor ampullate silks of orb-web weaving spiders are as tough as draglines, due to their higher extensibility despite lower strength. Differences in material properties between silk types result from differences in their component proteins, particularly members of the spidroin (spider fibroin) gene family. However, the extent to which variation in material properties within a single silk type can be explained by variation in spidroin sequences is unknown. Here, we compare the minor ampullate spidroins (MiSp) of orb-weavers and cobweb weavers. Orb-web weavers use minor ampullate silk to form the auxiliary spiral of the orb-web while cobweb weavers use it to wrap prey, suggesting that selection pressures on minor ampullate spidroins (MiSp) may differ between the two groups.
We report complete or nearly complete MiSp sequences from five cobweb weaving spider species and measure material properties of minor ampullate silks in a subset of these species. We also compare MiSp sequences and silk properties of our cobweb weavers to published data for orb-web weavers. We demonstrate that all our cobweb weavers possess multiple MiSp loci and that one locus is more highly expressed in at least two species. We also find that the proportion of β-spiral-forming amino acid motifs in MiSp positively correlates with minor ampullate silk extensibility across orb-web and cobweb weavers.
MiSp sequences vary dramatically within and among spider species, and have likely been subject to multiple rounds of gene duplication and concerted evolution, which have contributed to the diverse material properties of minor ampullate silks. Our sequences also provide templates for recombinant silk proteins with tailored properties.
圆网蛛及其近亲会使用多种特定任务的蛛丝。大多数蜘蛛丝研究都集中在主壶腹腺合成的超坚韧的牵引丝上，但其他类型的蛛丝也具有令人印象深刻的材料特性。例如，圆网蛛的小壶腹蛛丝尽管强度较低，但由于其更高的延展性，与牵引丝一样坚韧。不同类型蛛丝的材料特性差异源于其组成蛋白的差异，特别是蛛丝蛋白（蜘蛛纤维蛋白）基因家族的成员。然而，单一类型蛛丝的材料特性变化在多大程度上可以由蛛丝蛋白序列的变化来解释尚不清楚。在这里，我们比较了圆网蛛和 cobweb 编织者的小壶腹蛛丝蛋白（MiSp）。圆网蛛用小壶腹蛛丝形成圆网的辅助螺旋，而 cobweb 编织者用它来包裹猎物，这表明两组对小壶腹蛛丝蛋白（MiSp）的选择压力可能不同。
我们报告了来自五种 cobweb 编织蜘蛛物种的完整或几乎完整的 MiSp 序列，并测量了这些物种子集中小壶腹蛛丝的材料特性。我们还将我们的 cobweb 编织者的 MiSp 序列和蛛丝特性与已发表的圆网蛛数据进行了比较。我们证明，我们所有的 cobweb 编织者都拥有多个 MiSp 基因座，并且至少在两个物种中一个基因座表达更高。我们还发现，MiSp 中形成β-螺旋的氨基酸基序的比例与圆网蛛和 cobweb 编织者的小壶腹蛛丝延展性呈正相关。
MiSp 序列在蜘蛛物种内部和之间差异很大，并且可能经历了多轮基因复制和协同进化，这导致了小壶腹蛛丝的多种材料特性。我们的序列还为具有定制特性的重组蛛丝蛋白提供了模板。
