Division of Infection and Immunity, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, 3052, Australia.
Traffic. 2013 May;14(5):532-50. doi: 10.1111/tra.12053. Epub 2013 Feb 27.
Plasmodium falciparum exports several hundred effector proteins that remodel the host erythrocyte and enable parasites to acquire nutrients, sequester in the circulation and evade immune responses. The majority of exported proteins contain the Plasmodium export element (PEXEL; RxLxE/Q/D) in their N-terminus, which is proteolytically cleaved in the parasite endoplasmic reticulum by Plasmepsin V, and is necessary for export. Several exported proteins lack a PEXEL or contain noncanonical motifs. Here, we assessed whether Plasmepsin V could process the N-termini of diverse protein families in P. falciparum. We show that Plasmepsin V cleaves N-terminal sequences from RIFIN, STEVOR and RESA multigene families, the latter of which contain a relaxed PEXEL (RxLxxE). However, Plasmepsin V does not cleave the N-terminal sequence of the major exported virulence factor erythrocyte membrane protein 1 (PfEMP1) or the PEXEL-negative exported proteins SBP-1 or REX-2. We probed the substrate specificity of Plasmepsin V and determined that lysine at the PEXEL P3 position, which is present in PfEMP1 and other putatively exported proteins, blocks Plasmepsin V activity. Furthermore, isoleucine at position P1 also blocked Plasmepsin V activity. The specificity of Plasmepsin V is therefore exquisitely confined and we have used this novel information to redefine the predicted P. falciparum PEXEL exportome.
恶性疟原虫（Plasmodium falciparum）输出数百种效应蛋白，重塑宿主红细胞，使寄生虫能够获取营养物质、在循环中隔离并逃避免疫反应。大多数输出蛋白的 N 端含有疟原虫输出元件（PEXEL；RxLxE/Q/D），在寄生虫内质网中被 Plasmepsin V 蛋白水解切割，这对于输出是必需的。一些输出蛋白缺乏 PEXEL 或含有非典型基序。在这里，我们评估了 Plasmepsin V 是否可以处理恶性疟原虫中不同蛋白家族的 N 端。我们表明，Plasmepsin V 可切割 RIFIN、STEVOR 和 RESA 多基因家族的 N 端序列，后者包含松弛的 PEXEL（RxLxxE）。然而，Plasmepsin V 不会切割主要输出毒力因子红细胞膜蛋白 1（PfEMP1）或 PEXEL 阴性输出蛋白 SBP-1 或 REX-2 的 N 端序列。我们探测了 Plasmepsin V 的底物特异性，并确定 PfEMP1 和其他推测的输出蛋白中 PEXEL 上的 P3 位赖氨酸阻止了 Plasmepsin V 的活性。此外，P1 位的异亮氨酸也阻止了 Plasmepsin V 的活性。因此，Plasmepsin V 的特异性非常严格，我们利用这一新信息重新定义了预测的恶性疟原虫 PEXEL 外显子组。
