A unique cuboid spider silk from the outer egg sac of Nephila pilipes, with an unusual square cross-section, is disclosed. The structure-function relationships within this silk are first studied through structural characterization, mechanical measurement, protein conformation, and polypeptide signature of silk proteins. This silk maintains the higher stiffness property of egg sac silks, and also shows a species difference. Environmental response of the mechanical properties within this silk are observed. Synchrotron FTIR microspectroscopy is used to monitor the silk protein conformation in a single natural silk. The β-sheet structure aligns parallel to the fiber axis with a content of 22% ± 2.6%. The de novo resulting polypeptide from the solid silk fibers are novel, and an abundant polar amino acid insertion is observed. Short polyalanine (An , n ≤ 3), alternating serine and alanine (S/A)X, and alternating glycine and alanine (G/A)X, GGX, and SSX dominates in the resulting de novo polypeptide. This accords with the composition pattern of other egg sac silk proteins, besides the rarely observed GGX. This study broadens the library of egg sac spider silks and provides a new perspective to uncover structure-function relationships in spider silk.

中文翻译：

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长方体蜘蛛丝：结构-功能关系和多肽签名。

公开了一种来自Nephila pilipes外卵囊的独特长方体蜘蛛丝，具有不寻常的正方形横截面。首先通过结构表征，机械测量，蛋白质构象和丝绸蛋白的多肽标记研究这种丝绸中的结构-功能关系。这种丝保持了卵囊丝更高的刚度，并显示出种类差异。观察到该丝内机械性能的环境响应。同步加速器FTIR显微技术用于监测单个天然丝绸中的丝绸蛋白构象。β-折叠结构平行于纤维轴排列，含量为22％±2.6％。从固体丝纤维得到的从头产生的多肽是新颖的，并且观察到大量的极性氨基酸插入。短聚丙氨酸（An，n≤3），丝氨酸和丙氨酸交替（S / A）X和甘氨酸和丙氨酸交替（G / A）X，GGX和SSX在所得的新生多肽中占主导地位。除很少观察到的GGX外，这与其他卵囊丝蛋白的组成模式一致。该研究拓宽了卵囊蜘蛛丝的文库，并为揭示蜘蛛丝的结构-功能关系提供了新的视角。