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 Plasmodium berghei (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. Pbqsox deletion (Δpbqsox) did not affect asexual intraerythrocytic development, but reduced exflagellation of male gametocytes as well as formation and maturation of ookinetes. Pbqsox 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 Δpbqsox-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 in vitro and mosquito feeding assays, suggesting QSOX is a potential target for blocking parasite transmission.

存在于多种真核生物种中的Quiescin巯基氧化酶（QSOX）催化二硫键插入未折叠的还原蛋白中。在这里，我们从啮齿动物疟疾寄生虫中表征了QSOX蛋白伯氏疟原虫（PbQSOX），在所有测序的疟原虫物种中都是保守的。PbQSOX蛋白未在无性红细胞生成阶段表达，但在子代发育最丰富。间接免疫荧光分析表明，PbQSOX不仅位于配子细胞，配子和单核细胞的细胞质中，而且在配子和单核细胞的表面表达。Western印迹法鉴定了在提示分泌的分泌素的培养基中PbQSOX在细胞外的存在。b 删除（Δb）不会影响无性红细胞内发育，但会减少雄性配子细胞的鞭毛脱落以及速尿的形成和成熟。 b缺失还导致ookinete表面蛋白的还原硫醇基团的显着增加，这表明它可能在维持表面蛋白二硫键完整性方面起作用，这可能是ookinete开发所必需的。以Δ为食的蚊子b与饲喂野生型寄生虫感染的小鼠相比，被感染的小鼠的合子和卵囊数量显着减少。此外，多克隆小鼠抗血清和针对重组PbQSOX的单克隆抗体均在小鼠体内表现出实质性的传递阻断活性。体外 和蚊子喂养试验，表明QSOX是阻止寄生虫传播的潜在目标。