The toxoplasma micronemal protein MIC4 is an adhesin composed of six conserved apple domains
The toxoplasma micronemal protein MIC4 is an adhesin composed of six conserved apple domains
复制标题
DOI：
10.1074/jbc.m008294200
复制
发表时间：
2001-02-09
影响因子：
4.8
通讯作者：
Soldati, D
中科院分区：
文献类型：
--
作者：
Brecht, S;Carruthers, VB;Soldati, D
顶复门寄生虫入侵的初始阶段涉及含微线分子的胞吐作用，这些分子有助于宿主细胞附着和渗透。MIC 4是由弓形虫速殖子分泌的一种蛋白质，在微线体胞吐作用的刺激下分泌。我们对成熟蛋白进行了微测序，从微线体中排出后纯化，并克隆了相应的基因。MIC 4的推导的氨基酸序列预测了一个61 kDa的蛋白，包含6个保守的苹果结构域。Apple结构域由六个空间上保守的半胱氨酸残基组成，这些半胱氨酸残基形成二硫键，并且也存在于来自两种密切相关的顶复门寄生虫（鼠肉孢子虫和艾美耳球虫属物种）的微线蛋白以及几种哺乳动物血清蛋白（包括激肽释放酶）中。在这里，我们表明，MIC 4定位于所有入侵形式的T。弓形虫、速殖子、缓殖子、子孢子和裂殖子。蛋白质仅在从细胞器释放时在N和C末端进行蛋白水解加工。MIC 4有效地结合宿主细胞，并且粘附基序映射在最C-末端苹果结构域中。
The initial stage of invasion by apicomplexan parasites involves the exocytosis of the micronemes-containing molecules that contribute to host cell attachment and penetration. MIC4 was previously described as a protein secreted by Toxoplasma gondii tachyzoites upon stimulation of micronemes exocytosis. We have microsequenced the mature protein, purified after discharge from micronemes and cloned the corresponding gene. The deduced amino acid sequence of MIC4 predicts a 61-kDa protein that contains 6 conserved apple domains. Apple domains are composed of six spacely conserved cysteine residues which form disulfide bridges and are also present in micronemal proteins from two closely related apicomplexan parasites, Sarcocystis muris and Eimeria species, and several mammalian serum proteins, including kallikrein. Here we show that MIC4 localizes in the micronemes of all the invasive forms of T. gondii, tachyzoites, bradyzoites; sporozoites, and merozoites. The protein is proteolytically processed both at the N and the C terminus only upon release from the organelle. MIC4 binds efficiently to host cells, and the adhesive motif maps in the most C-terminal apple domain.