Eimeria tenella is an obligate intracellular parasite in the phylum Apicomplexa. As described for other members of Apicomplexa, apical membrane antigen 1 (AMA1) has been shown to be critical for sporozoite invasion of host cells by E. tenella. Recently, an E. tenella paralogue of AMA1 (EtAMA1), dubbed sporoAMA1 (EtAMA3), was identified in proteomic and transcriptomic analyses of E. tenella, but not further characterized. Here, we show that EtAMA3 is a type I integral membrane protein that has 24% -38% identity with other EtAMAs. EtAMA3 has the same pattern of Cys residues in domains I and II of AMA1 orthologs from apicomplexan parasites, but high variance in domain III, with all six invariant Cys residues absent. EtAMA3 expression was developmentally regulated at the mRNA and protein levels. EtAMA3 protein was detected in sporulated oocysts and sporozoites, but not in the unsporulated oocysts or second generation merozoites. EtAMA3 is secreted by micronemes and is primarily localized to the apical end of sporozoites during host-cell invasion. Additionally, pretreatment of sporozoites with rEtAMA3-specific antibodies substantially impeded their invasion into host cells. These results suggest EtAMA3 is a sporozoite-specific protein that is involved in host-cell sporozoite invasion.

中文翻译：

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一种新的顶膜抗原 3 在艾美球虫中的鉴定和表征

Eimeria tenella 是顶复门中的一种专性细胞内寄生虫。正如对 Apicomplexa 的其他成员所描述的那样，顶端膜抗原 1 (AMA1) 已被证明对 E.tenella 对宿主细胞的子孢子入侵至关重要。最近，在对球虫的蛋白质组学和转录组学分析中发现了一种名为 sporoAMA1 (EtAMA3) 的 AMA1 (EtAMA1) 球虫的旁系同源物，但没有进一步表征。在这里，我们表明 EtAMA3 是一种 I 型整合膜蛋白，与其他 EtAMA 具有 24%-38% 的同一性。EtAMA3 在来自顶复门寄生虫的 AMA1 直系同源物的结构域 I 和 II 中具有相同模式的 Cys 残基，但结构域 III 的差异很大，所有六个不变的 Cys 残基都不存在。EtAMA3 表达在 mRNA 和蛋白质水平上受到发育调控。EtAMA3 蛋白在孢子化卵囊和子孢子中检测到，但在非孢子化卵囊或第二代裂殖子中未检测到。EtAMA3 由微线虫分泌，在宿主细胞入侵期间主要定位于子孢子的顶端。此外，用 rEtAMA3 特异性抗体预处理子孢子大大阻碍了它们侵入宿主细胞。这些结果表明 EtAMA3 是一种子孢子特异性蛋白，参与宿主细胞子孢子的侵袭。