Department of Immunology, College of Basic Medical Sciences, China Medical University, Shenyang, China.
Department of Clinical Laboratory, Affiliated Hospital of Inner Mongolian Medical University, Hohhot, China.
Front Cell Infect Microbiol. 2020 Jun 26;10:311. doi: 10.3389/fcimb.2020.00311. eCollection 2020.
Quiescin sulfhydryl oxidase (QSOX), present in a wide variety of eukaryotic species, catalyzes the insertion of disulfide bonds into unfolded, reduced proteins. Here we characterized the QSOX protein from the rodent malaria parasite (PbQSOX), which is conserved in all sequenced malaria parasite species. The PbQSOX protein was not expressed in asexual erythrocytic stages, but was most abundantly expressed in ookinetes. Indirect immunofluorescence assays revealed PbQSOX was not only localized in cytoplasm of gametocytes, gametes and ookinetes, but also expressed on the surface of gametes and ookinetes. Western blot identified extracellular presence of PbQSOX in the culture medium of ookinetes suggestive of secretion. deletion (Δ) did not affect asexual intraerythrocytic development, but reduced exflagellation of male gametocytes as well as formation and maturation of ookinetes. deletion also led to a significant increase in the reduced thiol groups of ookinete surface proteins, suggesting that it may play a role in maintaining the integrity of disulfide bonds of surface proteins, which might be needed for ookinete development. Mosquitoes that fed on Δ-infected mice showed a significant reduction in ookinete and oocyst numbers compared to those fed on wild-type parasite-infected mice. Further, both polyclonal mouse antisera and a monoclonal antibody against the recombinant PbQSOX exhibited substantial transmission-blocking activities in and mosquito feeding assays, suggesting QSOX is a potential target for blocking parasite transmission.
静止硫氧还蛋白氧化酶（QSOX）存在于多种真核生物中，可催化将二硫键插入到未折叠的还原蛋白中。本文对来自啮齿动物疟原虫（PbQSOX）的 QSOX 蛋白进行了特征描述，该蛋白在所有测序的疟原虫物种中都保守。PbQSOX 蛋白在无性红细胞阶段不表达，但在动合子中表达最丰富。间接免疫荧光检测显示，PbQSOX 不仅定位于配子体、配子和动合子的细胞质中，还表达在配子和动合子的表面。Western blot 鉴定表明，PbQSOX 存在于动合子培养物的细胞外液中，提示其可能发生了分泌。Δ缺失（deletion）不影响无性红细胞内发育，但减少了雄性配子体的出尾以及动合子的形成和成熟。Δ缺失也导致动合子表面蛋白的还原硫醇基团显著增加，表明其可能在维持表面蛋白中二硫键的完整性中发挥作用，这可能是动合子发育所必需的。与感染野生型寄生虫的小鼠相比，感染 Δ 缺失的小鼠的蚊子摄食量显著减少了动合子和卵囊的数量。此外，多克隆鼠抗血清和针对重组 PbQSOX 的单克隆抗体在 和蚊子喂食试验中均表现出显著的阻断寄生虫传播的活性，表明 QSOX 是阻断寄生虫传播的潜在靶标。
