Inserted (I) domains function as ligand-binding domains in adhesins that support cell adhesion and migration in many eukaryotic phyla. These adhesins include integrin αβ heterodimers in metazoans and single subunit transmembrane proteins in apicomplexans such as TRAP in Plasmodium and MIC2 in Toxoplasma. Here we show that the I domain of TRAP is essential for sporozoite gliding motility, mosquito salivary gland invasion and mouse infection. Its replacement with the I domain from Toxoplasma MIC2 fully restores tissue invasion and parasite transmission, while replacement with the aX I domain from human integrins still partially restores liver infection. Mutations around the ligand binding site allowed salivary gland invasion but led to inefficient transmission to the rodent host. These results suggest that apicomplexan parasites appropriated polyspecific I domains in part for their ability to engage with multiple ligands and to provide traction for emigration into diverse organs in distant phyla.

中文翻译：

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进化上遥远的 I 结构域可以在功能上取代疟原虫 TRAP 的基本配体结合结构域

插入的 (I) 域在粘附素中作为配体结合域发挥作用，支持许多真核生物门中的细胞粘附和迁移。这些粘附素包括后生动物中的整合素 αβ 异二聚体和顶复动物中的单亚基跨膜蛋白，例如疟原虫中的 TRAP 和弓形虫中的 MIC2。在这里，我们表明 TRAP 的 I 域对于子孢子滑动运动、蚊子唾液腺入侵和小鼠感染至关重要。用来自弓形虫 MIC2 的 I 结构域替换它可以完全恢复组织侵袭和寄生虫传播，而用来自人类整合素的 aX I 结构域替换仍然部分恢复肝脏感染。配体结合位点周围的突变允许唾液腺侵入，但导致向啮齿动物宿主的低效传播。