Andersen Svend Olav, Roepstorff Peter
August Krogh Institute, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen O, Denmark.
Insect Biochem Mol Biol. 2005 Oct;35(10):1181-8. doi: 10.1016/j.ibmb.2005.05.009.
The proteins in the distensible alloscutal cuticle of the blood-feeding tick, Ixodes ricinus, have been characterized by electrophoresis and chromatography, two of the proteins were purified and their total amino acid sequence determined. They show sequence similarity to cuticular proteins from the spider, Araneus diadematus, and the horseshoe crab, Limulus polyphemus, and to a lesser extent to insect cuticular proteins. They contain a conserved sequence region, which is closely related to the chitin-binding Rebers-Riddiford consensus sequence present in many insect cuticular proteins. Only a fraction of the alloscutal proteins can be readily dissolved, and the dissolved proteins are difficult to separate by electrophoresis and column chromatography. The insoluble fraction can only be dissolved after degradation to smaller peptides. The mixture of extractable proteins as well as hydrolysates of the insoluble fraction are fluorescent when exposed to ultraviolet light, and the fluorescence corresponds in excitation and emission maxima to the fluorescence of the rubber-like arthropodan protein, resilin, and to the amino acid dityrosine. Small amounts of dityrosine were obtained from ticks in the early phase of a blood meal when the cuticle weighs less than 4 mg; increasing amounts were obtained from animals in the initial period of feeding, during which the cuticular weight increases from 4 to 11 mg, whereas little increase in dityrosine content was observed during the final period of engorgement. Cuticle from fully distended ticks contains about 60-80 nmole dityrosine per tick, corresponding to 2-3 microg/mg cuticle. It is suggested that the major part of the cuticular proteins is made inextractable by cross-linking by dityrosine residues, and that dityrosine plays a role in stabilizing the cuticular structure during the extensive distension occurring during a blood meal. Small amounts of 3-monochlorotyrosine and 3,5-dichlorotyrosine were obtained from the distended tick cuticle, corresponding to chlorination of between 0.5% and 1.5% of the tyrosine residues. It is suggested that the chlorotyrosines are a side-product of oxidative processes in the cuticle.
血食性蜱类蓖麻硬蜱（Ixodes ricinus）可扩张的盾板角质层中的蛋白质已通过电泳和色谱法进行了表征，其中两种蛋白质被纯化并测定了其完整氨基酸序列。它们与蜘蛛园蛛（Araneus diadematus）和鲎（Limulus polyphemus）的角质层蛋白具有序列相似性，与昆虫角质层蛋白的相似性较低。它们包含一个保守序列区域，该区域与许多昆虫角质层蛋白中存在的几丁质结合Rebers-Riddiford共有序列密切相关。只有一小部分盾板蛋白能够轻易溶解，并且溶解的蛋白质难以通过电泳和柱色谱法分离。不溶性部分只有在降解为较小的肽后才能溶解。可提取蛋白质的混合物以及不溶性部分的水解产物在紫外光照射下会发出荧光，其荧光的激发和发射最大值与橡胶状节肢动物蛋白弹性蛋白以及氨基酸二酪氨酸的荧光相对应。在血餐早期，当角质层重量小于4毫克时，从蜱中获得少量二酪氨酸；在进食初期，动物体内的二酪氨酸含量不断增加，在此期间角质层重量从4毫克增加到11毫克，而在饱食末期二酪氨酸含量几乎没有增加。完全饱胀的蜱的角质层每只蜱含有约60 - 80纳摩尔二酪氨酸，相当于2 - 3微克/毫克角质层。有人认为，角质层蛋白的主要部分通过二酪氨酸残基交联而变得不可提取，并且二酪氨酸在血餐期间发生的广泛扩张过程中对角质层结构的稳定起作用。从饱胀的蜱角质层中获得少量3 - 单氯酪氨酸和3,5 - 二氯酪氨酸，相当于酪氨酸残基氯化量的0.5%至1.5%。有人认为氯酪氨酸是角质层氧化过程的副产物。
