Silk from Crickets: A New Twist on Spinning

Raspy crickets (Orthoptera: Gryllacrididae) are unique among the orthopterans in producing silk, which is used to build shelters. This work studied the material composition and the fabrication of cricket silk for the first time. We examined silk-webs produced in captivity, which comprised cylindrical fibers and flat films. Spectra obtained from micro-Raman experiments indicated that the silk is composed of protein, primarily in a beta-sheet conformation, and that fibers and films are almost identical in terms of amino acid composition and secondary structure. The primary sequences of four silk proteins were identified through a mass spectrometry/cDNA library approach. The most abundant silk protein was large in size (300 and 220 kDa variants), rich in alanine, glycine and serine, and contained repetitive sequence motifs; these are features which are shared with several known beta-sheet forming silk proteins. Convergent evolution at the molecular level contrasts with development by crickets of a novel mechanism for silk fabrication. After secretion of cricket silk proteins by the labial glands they are fabricated into mature silk by the labium-hypopharynx, which is modified to allow the controlled formation of either fibers or films. Protein folding into beta-sheet structure during silk fabrication is not driven by shear forces, as is reported for other silks.锉蟋（Raspy cricket，直翅目Orthoptera：驼螽科Gryllacrididae）是直翅目昆虫中唯一可产丝的类群，所产丝用于构筑栖息庇护结构。本研究首次针对锉蟋丝的物质组成与制备过程展开系统探究。我们对人工饲养条件下产出的蟋丝制品进行了分析，其结构包含圆柱形纤维与扁平薄膜两种形态。微拉曼光谱实验获得的光谱数据显示，该丝的主要成分为蛋白质，且主要以β折叠（beta-sheet）构象存在；同时，圆柱形纤维与扁平薄膜的氨基酸组成与二级结构几乎完全一致。研究人员通过质谱（mass spectrometry）/ cDNA文库（cDNA library）联用技术，鉴定出四种蟋丝蛋白的一级序列。丰度最高的蟋丝蛋白分子量较大，存在300 kDa与220 kDa两种变体，富含丙氨酸、甘氨酸与丝氨酸，并含有重复序列基序；这些特征与多种已报道的β折叠型丝蛋白高度相似。分子层面的趋同演化（convergent evolution）与锉蟋所演化出的全新丝蛋白制备机制形成鲜明反差。锉蟋的下唇腺（labial gland）分泌丝蛋白后，再通过特化的下唇-下咽腔复合体（labium-hypopharynx）将其加工为成熟丝；该结构经过适应性特化，可精准调控纤维或薄膜的定向形成。与其他已知丝蛋白的加工过程不同，锉蟋丝在制备过程中，其蛋白质折叠为β折叠结构的过程并非由剪切力（shear forces）驱动。