Department of Chemistry & Biochemistry, University of California, San Diego, La Jolla, California, United States of America.
Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California, San Diego, La Jolla, California, United States of America.
PLoS Pathog. 2022 Sep 14;18(9):e1010829. doi: 10.1371/journal.ppat.1010829. eCollection 2022 Sep.
Multidrug-resistant (MDR) Enterococcus faecalis are major causes of hospital-acquired infections. Numerous clinical strains of E. faecalis harbor a large pathogenicity island that encodes enterococcal surface protein (Esp), which is suggested to promote biofilm production and virulence, but this remains controversial. To resolve this issue, we characterized the Esp N-terminal region, the portion implicated in biofilm production. Small angle X-ray scattering indicated that the N-terminal region had a globular head, which consisted of two DEv-Ig domains as visualized by X-ray crystallography, followed by an extended tail. The N-terminal region was not required for biofilm production but instead significantly strengthened biofilms against mechanical or degradative disruption, greatly increasing retention of Enterococcus within biofilms. Biofilm strengthening required low pH, which resulted in Esp unfolding, aggregating, and forming amyloid-like structures. The pH threshold for biofilm strengthening depended on protein stability. A truncated fragment of the first DEv-Ig domain, plausibly generated by a host protease, was the least stable and sufficient to strengthen biofilms at pH ≤ 5.0, while the entire N-terminal region and intact Esp on the enterococcal surface was more stable and required a pH ≤ 4.3. These results suggested a virulence role of Esp in strengthening enterococcal biofilms in acidic abiotic or host environments.
耐多药（MDR）粪肠球菌是医院获得性感染的主要原因。大量临床粪肠球菌菌株携带一个大型的致病性岛，该岛编码肠球菌表面蛋白（Esp），这被认为有助于生物膜的产生和毒力，但这仍然存在争议。为了解决这个问题，我们对 Esp 的 N 端区域进行了表征，该区域与生物膜的产生有关。小角度 X 射线散射表明，N 端区域具有球状头部，通过 X 射线晶体学观察到该头部由两个 DEv-Ig 结构域组成，后面是一个延伸的尾部。N 端区域不是生物膜产生所必需的，但它显著增强了生物膜对机械或降解破坏的抵抗力，大大增加了肠球菌在生物膜内的保留。生物膜的增强需要低 pH 值，这导致 Esp 展开、聚集并形成类似淀粉样的结构。生物膜增强的 pH 阈值取决于蛋白质的稳定性。第一 DEv-Ig 结构域的截断片段，可能是由宿主蛋白酶产生的，在 pH≤5.0 时最不稳定，足以增强生物膜，而完整的 Esp 和位于肠球菌表面的整个 N 端区域更稳定，需要 pH≤4.3。这些结果表明 Esp 在酸性非生物或宿主环境中增强肠球菌生物膜的毒力作用。
