National Animal Protozoa Laboratory, College of Veterinary Medicine, China Agricultural University, Beijing, China.
Key Laboratory of Animal Epidemiology of the Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, Beijing, China.
FASEB J. 2021 Dec;35(12):e21898. doi: 10.1096/fj.202100662RR.
Toxoplasma gondii is an obligate intracellular apicomplexan parasite causing lethal diseases in immunocompromised patients. UBL-UBA shuttle proteins (DDI1, RAD23, and DSK2) are important components of the ubiquitin-proteasome system. By degrading ubiquitinated proteins, UBL-UBA shuttle proteins regulate many cellular processes. However, the specific processes regulated by UBL-UBA shuttle proteins remain elusive. Here, we revealed that the deletion of shuttle proteins results in a selective accumulation of ubiquitinated proteins in the nucleus and aberrant DNA replication. ROP18 was mistargeted and accumulated in the shuttle protein mutant strain, resulting in the recruitment of immunity-related GTPases to the parasitophorous vacuole membrane (PVM). Furthermore, the mistargeting of ROP18 and the recruitment of Irgb6 to the PVM were also observed in the DDI1 mutant strain. DDI1 is a nonclassical UBL-UBA shuttle protein homologous to the HIV-1 protease. Molecular docking showed that DDI1 was a potential target of HIV-1 protease inhibitors. However, these inhibitors blocked the growth of T gondii in vitro but not in vivo. In conclusion, the Toxoplasma UBL-UBA shuttle protein regulates several important cellular processes and the mistargeting of ROP18 may be a representative of the abnormal homeostasis caused by shuttle protein mutation.
刚地弓形虫是一种专性细胞内顶复门寄生虫，可导致免疫功能低下患者的致命疾病。UBL-UBA 穿梭蛋白（DDI1、RAD23 和 DSK2）是泛素蛋白酶体系统的重要组成部分。通过降解泛素化蛋白，UBL-UBA 穿梭蛋白调节许多细胞过程。然而，UBL-UBA 穿梭蛋白调节的具体过程仍不清楚。在这里，我们揭示了穿梭蛋白的缺失导致核内泛素化蛋白的选择性积累和异常的 DNA 复制。ROP18 被错误靶向并在穿梭蛋白突变株中积累，导致免疫相关 GTPases 募集到寄生泡膜（PVM）。此外，在 DDI1 突变株中也观察到 ROP18 的错误靶向和 Irgb6 募集到 PVM。DDI1 是一种与 HIV-1 蛋白酶同源的非经典 UBL-UBA 穿梭蛋白。分子对接表明 DDI1 是 HIV-1 蛋白酶抑制剂的潜在靶标。然而，这些抑制剂在体外抑制了弓形虫的生长，但在体内没有。总之，弓形虫 UBL-UBA 穿梭蛋白调节几个重要的细胞过程，ROP18 的错误靶向可能是穿梭蛋白突变引起的异常动态平衡的代表。
