Burmester T
Institute of Zoology, University of Mainz, D-55099 Mainz, Germany.
J Biol Chem. 1999 May 7;274(19):13217-22. doi: 10.1074/jbc.274.19.13217.
Copper-containing hemocyanins serve to transport oxygen in many arthropod species. Here I describe the identification and cDNA cloning of a structurally closely related non-respiratory pseudo-hemocyanin (PHc) of the American lobster, Homarus americanus. This protein has lost the ability to bind copper and, therefore, oxygen because a histidine residue in copper-binding site A is replaced by tyrosine. Like many arthropod hemocyanins, PHc forms a hexamer. It consists of two different subunit types of 660 and 661 amino acids, respectively, that share a 94.4% sequence identity. Whereas Homarus hemocyanin is produced in the hepatopancreas, PHc is synthesized by the ovaries and the heart tissue. Because different levels of PHc were observed in distinct individuals, I propose an association of the synthesis of this protein with the molting or reproduction cycle, similar to the hexamerins, insect storage proteins that are also related to the hemocyanins. However, phylogenetic analyses show that PHc derived independently from crustacean hemocyanins. Therefore, Homarus PHc is a member of a new class within the growing hemocyanin protein superfamily.
含铜血蓝蛋白在许多节肢动物物种中负责运输氧气。在此，我描述了美洲龙虾（美洲螯龙虾）一种结构上密切相关的非呼吸性假血蓝蛋白（PHc）的鉴定及cDNA克隆。由于铜结合位点A中的一个组氨酸残基被酪氨酸取代，该蛋白失去了结合铜进而结合氧气的能力。与许多节肢动物血蓝蛋白一样，PHc形成六聚体。它由两种不同的亚基类型组成，分别含有660和661个氨基酸，序列同一性为94.4%。美洲螯龙虾血蓝蛋白在肝胰腺中产生，而PHc由卵巢和心脏组织合成。由于在不同个体中观察到不同水平的PHc，我推测这种蛋白质的合成与蜕皮或繁殖周期有关，类似于六聚蛋白，即同样与血蓝蛋白相关的昆虫储存蛋白。然而，系统发育分析表明，PHc是从甲壳类血蓝蛋白独立衍生而来的。因此，美洲螯龙虾PHc是不断扩大的血蓝蛋白超家族中一个新类别的成员。
