Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, NE 68588;
Nebraska Center for Integrated Biomolecular Communication, University of Nebraska-Lincoln, Lincoln, NE 68588.
Proc Natl Acad Sci U S A. 2021 Apr 13;118(15). doi: 10.1073/pnas.2024651118.
The bacterium causes severe, sometimes lethal gastrointestinal disorders in humans, including enteritis and enterotoxemia. Type F strains produce an enterotoxin (CpE) that causes the third most common foodborne illness in the United States. CpE induces gut breakdown by disrupting barriers at cell-cell contacts called tight junctions (TJs), which are formed and maintained by claudins. Targeted binding of CpE to specific claudins, encoded by its C-terminal domain (cCpE), loosens TJ barriers to trigger molecular leaks between cells. Cytotoxicity results from claudin-bound CpE complexes forming pores in cell membranes. In mammalian tissues, ∼24 claudins govern TJ barriers-but the basis for CpE's selective targeting of claudins in the gut was undetermined. We report the structure of human claudin-4 in complex with cCpE, which reveals that enterotoxin targets a motif conserved in receptive claudins and how the motif imparts high-affinity CpE binding to these but not other subtypes. The structural basis of CpE targeting is supported by binding affinities, kinetics, and half-lives of claudin-enterotoxin complexes and by the cytotoxic effects of CpE on claudin-expressing cells. By correlating the binding residence times of claudin-CpE complexes we determined to claudin expression patterns in the gut, we uncover that the primary CpE receptors differ in mice and humans due to sequence changes in the target motif. These findings provide the molecular and structural element CpE employs for subtype-specific targeting of claudins during pathogenicity of in the gut and a framework for new strategies to treat CpE-based illnesses in domesticated mammals and humans.
这种细菌会导致人类严重的、有时甚至致命的胃肠道疾病，包括肠炎和肠毒血症。F 型菌株会产生一种肠毒素（CpE），这是美国第三常见的食源性疾病的病因。CpE 通过破坏细胞间的紧密连接（TJ）来破坏屏障，从而导致肠道破裂，这些 TJ 是由紧密连接蛋白（Claudins）形成和维持的。CpE 通过其 C 末端结构域（cCpE）与特定 Claudin 的靶向结合，松开 TJ 屏障，引发细胞间的分子渗漏。细胞毒性是由 Claudin 结合的 CpE 复合物在细胞膜上形成孔引起的。在哺乳动物组织中，约 24 种 Claudin 控制着 TJ 屏障，但 CpE 对肠道 Claudin 的选择性靶向的基础尚不清楚。我们报告了人 Claudin-4 与 cCpE 复合物的结构，该结构揭示了肠毒素靶向接受性 Claudin 中保守的基序，以及该基序如何赋予 Claudin 高亲和力的 CpE 结合，而不是其他亚型。CpE 靶向的结构基础得到了 Claudin-肠毒素复合物的结合亲和力、动力学和半衰期以及 CpE 对 Claudin 表达细胞的细胞毒性的支持。通过将 Claudin-CpE 复合物的结合停留时间与 Claudin 在肠道中的表达模式相关联，我们发现由于靶标基序的序列变化，CpE 的主要受体在小鼠和人类中存在差异。这些发现为 CpE 在肠道致病性过程中针对 Claudin 的亚型特异性靶向提供了分子和结构基础，并为治疗家养哺乳动物和人类基于 CpE 的疾病提供了新的策略框架。
