State Key Laboratory of Pathogens and Biosecurity, Academy of Military Medical Sciences, Beijing 100071, China.
School of Basic Medical Science, Anhui Medical University, Hefei 230032, China.
Genes (Basel). 2024 Sep 26;15(10):1250. doi: 10.3390/genes15101250.
Many Gram-negative enterobacteria translocate virulence proteins (effectors) into intestinal epithelial cells using a type III secretion system (T3SS) to subvert the activity of various cell functions possess. Many T3SS effectors have been extensively characterized, but there are still some effector proteins whose functional information is completely unknown.
In this study, two predicted effectors of unknown function, EspN and EspS ( secreted protein N and S), were selected for analysis of translocation, distribution and structure prediction.
The TEM1 (β-lactamase) translocation assay was performed, which showed that EspN and EspS are translocated into host cells in a T3SS-dependent manner during bacterial infection. A phylogenetic tree analysis revealed that homologs of EspN and EspS are widely distributed in pathogenic bacteria. Multiple sequence alignment revealed that EspN and its homologs share a conserved C-terminal region (673-1133 a.a.). Furthermore, the structure of EspN (673-1133 a.a.) was also predicted and well-defined, which showed that it has three subdomains connected by a loop region. EspS and its homologs share a sequence-conserved C-terminal (146-291 a.a.). The predicted structure of EspS (146-291 a.a.) is composed of a β-sheet consisting of four β-strands and several short helices, which has a TM score of 0.5014 with the structure of the RTX cysteine protease domain (PDBID: 3eeb).
These results suggest that EspN and EspS may represent two important classes of T3SS effectors associated with pathogen virulence, and our findings provide important clues to understanding the potential functions of EspN and EspS.
许多革兰氏阴性肠杆菌使用 III 型分泌系统（T3SS）将毒力蛋白（效应子）易位到肠上皮细胞中，从而颠覆各种细胞功能的活性。许多 T3SS 效应子已经得到了广泛的研究，但仍有一些效应蛋白的功能信息完全未知。
本研究选择了两个预测的未知功能效应子 EspN 和 EspS（分泌蛋白 N 和 S）进行易位、分布和结构预测分析。
进行 TEM1（β-内酰胺酶）易位测定，结果表明 EspN 和 EspS 在细菌感染过程中以 T3SS 依赖的方式易位到宿主细胞中。系统发育树分析显示，EspN 和 EspS 的同源物广泛分布于病原菌中。多重序列比对显示，EspN 和其同源物共享一个保守的 C 端区域（673-1133 个氨基酸）。此外，还预测了 EspN（673-1133 个氨基酸）的结构，并得到了很好的定义，表明它具有三个由环区连接的亚结构域。EspS 和其同源物共享一个序列保守的 C 端（146-291 个氨基酸）。EspS（146-291 个氨基酸）的预测结构由一个由四个β-链和几个短螺旋组成的β-片层组成，与 RTX 半胱氨酸蛋白酶结构域（PDBID：3eeb）的 TM 评分为 0.5014。
这些结果表明 EspN 和 EspS 可能代表与病原体毒力相关的两类重要的 T3SS 效应子，我们的研究结果为理解 EspN 和 EspS 的潜在功能提供了重要线索。
