Insect silks are secreted from diverse gland types; this chapter deals with the silks produced by labial glands of Holometabola (insects with pupa in their life cycle). Labial silk glands are composed of a few tens or hundreds of large polyploid cells that secrete polymerizing proteins which are stored in the gland lumen as a semi-liquid gel. Polymerization is based on weak molecular interactions between repetitive amino acid motifs present in one or more silk proteins; cross-linking by disulfide bonds may be important in the silks spun under water. The mechanism of long-term storage of the silk dope inside the glands and its conversion into the silk fiber during spinning is not fully understood. The conversion occurs within seconds at ambient temperature and pressure, under minimal drawing force and in some cases under water. The silk filament is largely built of proteins called fibroins and in Lepidoptera and Trichoptera coated by glue-type proteins known as sericins. Silks often contain small amounts of additional proteins of poorly known function. The silk components controlling dope storage and filament formation seem to be conserved at the level of orders, while the nature of polymerizing motifs in the fibroins, which determine the physical properties of silk, differ at the level of family and even genus. Most silks are based on fibroin beta-sheets interrupted with other structures such as alpha-helices but the silk proteins of certain sawflies have predominantly a collagen-like or polyglycine II arrangement and the silks of social Hymenoptera are formed from proteins in a coiled coil arrangement.

中文翻译：

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由昆虫唇腺产生的丝。

昆虫丝由不同类型的腺体分泌。本章讨论由全变态虫（Holometabola）（生命周期中有蛹的昆虫）的唇腺产生的丝。唇丝腺由几十或数百个大的多倍体细胞组成，这些细胞分泌聚合蛋白，这些蛋白以半液体凝胶的形式储存在腺腔中。聚合基于一种或多种丝蛋白中存在的重复氨基酸基序之间的弱分子相互作用；二硫键交联对于水纺丝可能很重要。丝原液在腺体内长期储存及其在纺丝过程中转化为丝纤维的机制尚不完全清楚。在环境温度和压力下，在最小的拉力下，并且在某些情况下在水下，转化在几秒钟内发生。丝丝主要由称为丝蛋白的蛋白质构成，并且在鳞翅目和毛翅目中被称为丝胶的胶型蛋白质覆盖。蚕丝通常含有少量功能鲜为人知的附加蛋白质。控制丝液储存和长丝形成的丝成分似乎在目水平上是保守的，而丝心蛋白中决定丝的物理性质的聚合基序的性质在科甚至属水平上​​有所不同。大多数丝基于被其他结构（例如α螺旋）打断的丝心蛋白β-片层，但某些锯蝇的丝蛋白主要具有胶原蛋白样或多聚甘氨酸II排列，而社会膜翅目的丝由盘绕线圈排列的蛋白质形成。