Orb-weaving spiders produce up to seven silk types, each with distinct biological roles, protein compositions, and mechanics. Pyriform (or piriform) silk is composed of pyriform spidroin 1 (PySp1) and is the fibrillar component of attachment discs that attach webs to substrates and to each other. Here, we characterize the 234-residue repeat unit (the "Py unit") from the core repetitive domain of Argiope argentata PySp1. Solution-state nuclear magnetic resonance (NMR) spectroscopy-based backbone chemical shift and dynamics analysis demonstrate a structured core flanked by disordered tails, structuring that is maintained in a tandem protein of two connected Py units, indicative of structural modularity of the Py unit in the context of the repetitive domain. Notably, AlphaFold2 predicts the Py unit structure with low confidence, echoing low confidence and poor agreement to the NMR-derived structure for the Argiope trifasciata aciniform spidroin (AcSp1) repeat unit. Rational truncation, validated through NMR spectroscopy, provided a 144-residue construct retaining the Py unit core fold, enabling near-complete backbone and side chain 1H, 13C, and 15N resonance assignment. A six α-helix globular core is inferred, flanked by regions of intrinsic disorder that would link helical bundles in tandem repeat proteins in a beads-on-a-string architecture.

中文翻译：

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梨状蜘蛛蛋白 1 核心重复结构域的结构特征、内在无序和模块化。

球织蜘蛛可产生多达七种丝类型，每种类型都有不同的生物学作用、蛋白质组成和力学。梨状（或称梨状）丝由梨状蜘蛛蛋白 1 (PySp1) 组成，是连接盘的纤维成分，该盘将网附着在基材上以及彼此之间。在这里，我们表征了 Argiope argentata PySp1 核心重复结构域的 234 个残基重复单元（“Py 单元”）。基于溶液态核磁共振 (NMR) 光谱的主链化学位移和动力学分析证明了侧翼无序尾部的结构化核心，该结构维持在两个连接的 Py 单元的串联蛋白质中，表明 Py 单元的结构模块化重复域的上下文。值得注意的是，AlphaFold2 预测 Py 单元结构的置信度较低，与 NMR 衍生的 Argiope trifasciata 腺泡蛋白 (AcSp1) 重复单元结构的置信度较低且一致性较差。通过核磁共振波谱验证的合理截断提供了保留 Py 单元核心折叠的 144 个残基结构，实现了近乎完整的主链和侧链 1H、13C 和 15N 共振分配。推断出一个六 α 螺旋球状核心，其两侧是内在无序区域，这些区域将串联重复蛋白中的螺旋束连接成串珠结构。