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PEXEL 是一个蛋白水解成熟位点,对于分泌蛋白和非分泌蛋白都是如此。

PEXEL is a proteolytic maturation site for both exported and non-exported proteins.

机构信息

Department of Biomedical Sciences, Iowa State University, Ames, lowa, USA.

Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa, USA.

出版信息

mSphere. 2024 Feb 28;9(2):e0039323. doi: 10.1128/msphere.00393-23. Epub 2024 Feb 9.

Abstract

Obligate intracellular malaria parasites dramatically remodel their erythrocyte host through effector protein export to create a niche for survival. Most exported proteins contain a pentameric port ement (PEXEL)/host-targeting motif that is cleaved in the parasite ER by the aspartic protease Plasmepsin V (PMV). This processing event exposes a mature N terminus required for translocation into the host cell and is not known to occur in non-exported proteins. Here, we report that the non-exported parasitophorous vacuole protein UIS2 contains a PEXEL motif that is processed in the blood stage. While the N termini of exported proteins containing the PEXEL and immediately downstream ~10 residues are sufficient to mediate translocation into the RBC, the equivalent UIS2 N terminus does not promote the export of a reporter. Curiously, the UIS2 PEXEL contains an unusual aspartic acid at the fourth position, which constitutes the extreme N-terminal residue following PEXEL cleavage (P1', RIL↓DE). Using a series of chimeric reporter fusions, we show that Asp at P1' is permissive for PMV processing but abrogates export. Moreover, mutation of this single UIS2 residue to alanine enables export, reinforcing that the mature N terminus mediates export, not PEXEL processing . Prompted by this observation, we further show that PEXEL sequences in the N termini of other non-exported rhoptry proteins are also processed, suggesting that PMV may be a more general secretory maturase than previously appreciated, similar to orthologs in related apicomplexans. Our findings provide new insight into the unique N-terminal constraints that mark proteins for export.IMPORTANCEHost erythrocyte remodeling by malaria parasite-exported effector proteins is critical to parasite survival and disease pathogenesis. In the deadliest malaria parasite , most exported proteins undergo proteolytic maturation via recognition of the pentameric port ement (PEXEL)/host-targeting motif by the aspartic protease Plasmepsin V, which exposes a mature N terminus that is conducive for export into the erythrocyte host cell. While PEXEL processing is considered a unique mark of exported proteins, we demonstrate that PEXEL motifs are present and processed in non-exported proteins. Importantly, we show that specific residues at the variable fourth position of the PEXEL motif inhibit export despite being permissive for processing, reinforcing that features of the mature N terminus, and not PEXEL cleavage, identify cargo for export. This opens the door to further inquiry into the nature and evolution of the PEXEL motif.

摘要

疟原虫必需在细胞内寄生,通过效应蛋白的输出对红细胞宿主进行显著重塑,从而为自身生存创造小生境。大多数输出蛋白都含有五聚体输出元件(PEXEL)/宿主靶向基序,该基序在寄生虫内质网中被天冬氨酸蛋白酶 Plasmepsin V(PMV)切割。该加工事件暴露了一个成熟的 N 末端,该末端对于易位进入宿主细胞是必需的,并且据知不会在非输出蛋白中发生。在这里,我们报告说非输出的噬菌泡蛋白 UIS2 含有 PEXEL 基序,该基序在血期被加工。虽然含有 PEXEL 基序和紧接着的~10 个残基的输出蛋白的 N 末端足以介导易位进入 RBC,但等效的 UIS2 N 末端不能促进报告蛋白的输出。奇怪的是,UIS2 PEXEL 在第四个位置含有一个不寻常的天冬氨酸,该天冬氨酸构成 PEXEL 切割后(P1',RIL↓DE)的极端 N 末端残基。使用一系列嵌合报告融合物,我们表明 P1'处的天冬氨酸允许 PMV 加工,但会阻止输出。此外,将该 UIS2 残基的单个突变突变为丙氨酸可实现输出,这进一步证实成熟的 N 末端介导输出,而不是 PEXEL 加工。受此观察结果的启发,我们进一步表明,其他非输出的棒状体蛋白的 N 末端的 PEXEL 序列也被加工,这表明 PMV 可能是一种比以前认为的更为普遍的分泌成熟酶,类似于相关顶复门生物中的同源物。我们的发现为标记蛋白输出的独特 N 末端限制提供了新的见解。

重要性

疟原虫通过输出效应蛋白对红细胞宿主的重塑对寄生虫的生存和发病机制至关重要。在最致命的疟原虫中,大多数输出蛋白通过天冬氨酸蛋白酶 Plasmepsin V 识别五聚体输出元件(PEXEL)/宿主靶向基序进行蛋白水解成熟,从而暴露一个有利于易位进入红细胞宿主细胞的成熟 N 末端。虽然 PEXEL 加工被认为是输出蛋白的独特标志,但我们证明 PEXEL 基序存在于非输出蛋白中,并被加工。重要的是,我们表明 PEXEL 基序中的可变第四个位置的特定残基尽管允许加工,但仍会抑制输出,这进一步证实了成熟 N 末端的特征,而不是 PEXEL 切割,确定了输出的货物。这为进一步研究 PEXEL 基序的性质和进化打开了大门。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/c849/10900883/89c07e466378/msphere.00393-23.f001.jpg

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