Institute for the Biotechnology of Infectious Diseases, University of Technology, Sydney, Broadway, N.S.W. 2007, Australia.
BMC Genomics. 2012 Dec 7;13:685. doi: 10.1186/1471-2164-13-685.
Proteases regulate pathogenesis in apicomplexan parasites but investigations of proteases have been largely confined to the asexual stages of Plasmodium falciparum and Toxoplasma gondii. Thus, little is known about proteases in other Apicomplexa, particularly in the sexual stages. We screened the Eimeria tenella genome database for proteases, classified these into families and determined their stage specific expression.
Over forty protease genes were identified in the E. tenella genome. These were distributed across aspartic (three genes), cysteine (sixteen), metallo (fourteen) and serine (twelve) proteases. Expression of at least fifteen protease genes was upregulated in merozoites including homologs of genes known to be important in host cell invasion, remodelling and egress in P. falciparum and/or T. gondii. Thirteen protease genes were specifically expressed or upregulated in gametocytes; five of these were in two families of serine proteases (S1 and S8) that are over-represented in the coccidian parasites, E. tenella and T. gondii, distinctive within the Apicomplexa because of their hard-walled oocysts. Serine protease inhibitors prevented processing of EtGAM56, a protein from E. tenella gametocytes that gives rise to tyrosine-rich peptides that are incorporated into the oocyst wall.
Eimeria tenella possesses a large number of protease genes. Expression of many of these genes is upregulated in asexual stages. However, expression of almost one-third of protease genes is upregulated in, or confined to gametocytes; some of these appear to be unique to the Coccidia and may play key roles in the formation of the oocyst wall, a defining feature of this group of parasites.
蛋白酶在顶复门寄生虫的发病机制中起调节作用，但对蛋白酶的研究主要局限于疟原虫和刚地弓形虫的无性阶段。因此，人们对其他顶复门寄生虫中的蛋白酶知之甚少，特别是在有性阶段。我们在柔嫩艾美耳球虫基因组数据库中筛选了蛋白酶，将这些蛋白酶分类为家族，并确定了它们的阶段特异性表达。
在柔嫩艾美耳球虫基因组中鉴定出超过四十种蛋白酶基因。这些基因分布在天冬氨酸（三个基因）、半胱氨酸（十六个）、金属（十四个）和丝氨酸（十二个）蛋白酶中。至少十五种蛋白酶基因在裂殖子中上调表达，包括与宿主细胞入侵、重塑和出芽在疟原虫和/或刚地弓形虫中重要的基因的同源物。十三种蛋白酶基因在配子体中特异性表达或上调表达；其中五个基因属于丝氨酸蛋白酶家族（S1 和 S8），在球虫寄生虫，柔嫩艾美耳球虫和刚地弓形虫中过度表达，在顶复门寄生虫中是独特的，因为它们有坚硬的卵囊。丝氨酸蛋白酶抑制剂可防止 EtGAM56 的加工，EtGAM56 是柔嫩艾美耳球虫配子体中的一种蛋白质，可产生富含酪氨酸的肽，这些肽被纳入卵囊壁。
柔嫩艾美耳球虫拥有大量的蛋白酶基因。许多这些基因的表达在无性阶段上调。然而，几乎三分之一的蛋白酶基因的表达上调，或局限于配子体；其中一些似乎是球虫特有的，可能在卵囊壁的形成中发挥关键作用，卵囊壁是这群寄生虫的一个特征。
