Irgb6 is a priming immune-related GTPase (IRG) that counteracts Toxoplasma gondii. It is known to be recruited to the low virulent type II T. gondii parasitophorous vacuole (PV), initiating cell-autonomous immunity. However, the molecular mechanism by which immunity-related GTPases become inactivated after the parasite infection remains obscure. Here, we found that Thr95 of Irgb6 is prominently phosphorylated in response to low virulent type II T. gondii infection. We observed that a phosphomimetic T95D mutation in Irgb6 impaired its localization to the PV and exhibited reduced GTPase activity in vitro. Structural analysis unveiled an atypical conformation of nucleotide-free Irgb6-T95D, resulting from a conformational change in the G-domain that allosterically modified the PV membrane-binding interface. In silico docking corroborated the disruption of the physiological membrane binding site. These findings provide novel insights into a T. gondii-induced allosteric inactivation mechanism of Irgb6.

中文翻译：

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弓形虫通过开关 I 磷酸化灭活 Irgb6 的结构基础

Irgb6 是一种启动免疫相关 GTP 酶 (IRG)，可对抗弓形虫。已知它会被招募到低毒力的 II 型弓形虫寄生液泡 (PV)，从而启动细胞自主免疫。然而，免疫相关 GTP 酶在寄生虫感染后失活的分子机制仍不清楚。在这里，我们发现 Irgb6 的 Thr95 在低毒力 II 型弓形虫感染中显着磷酸化。我们观察到 Irgb6 中的磷酸模拟 T95D 突变损害了其对 PV 的定位，并在体外表现出 GTPase 活性降低。结构分析揭示了无核苷酸 Irgb6-T95D 的非典型构象，这是由于 G 结构域的构象变化导致 PV 膜结合界面发生变构修饰。计算机对接证实了生理膜结合位点的破坏。这些发现为弓形虫诱导的 Irgb6 变构失活机制提供了新的见解。