Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX 78712, USA.
Department of Chemical Engineering, The University of Texas at Austin, Austin, TX 78712, USA.
Cell Rep. 2022 Aug 16;40(7):111196. doi: 10.1016/j.celrep.2022.111196.
Integrins are ubiquitous cell-surface heterodimers that are exploited by pathogens and toxins, including leukotoxins that target β integrins on phagocytes. The Bordetella adenylate cyclase toxin (ACT) uses the αβ integrin as a receptor, but the structural basis for integrin binding and neutralization by antibodies is poorly understood. Here, we use cryoelectron microscopy to determine a 2.7 Å resolution structure of an ACT fragment bound to αβ. This structure reveals that ACT interacts with the headpiece and calf-2 of the α subunit in a non-canonical manner specific to bent, inactive αβ. Neutralizing antibody epitopes map to ACT residues involved in α binding, providing the basis for antibody-mediated attachment inhibition. Furthermore, binding to αβ positions the essential ACT acylation sites, which are conserved among toxins exported by type I secretion systems, at the cell membrane. These findings reveal a structural mechanism for integrin-mediated attachment and explain antibody-mediated neutralization of ACT intoxication.
整合素是普遍存在的细胞表面异二聚体，被病原体和毒素利用，包括靶向吞噬细胞β整合素的白细胞毒素。博德特氏菌腺苷酸环化酶毒素 (ACT) 使用 αβ 整合素作为受体，但抗体结合和中和整合素的结构基础理解得很差。在这里，我们使用冷冻电子显微镜确定了与 αβ 结合的 ACT 片段的 2.7 Å 分辨率结构。该结构表明，ACT 以一种非典型的方式与 α 亚基的头盖骨和小牛-2 相互作用，这种方式特异性地针对弯曲的、非活性的 αβ。中和抗体表位映射到参与 α 结合的 ACT 残基上，为抗体介导的附着抑制提供了基础。此外，与 αβ 的结合将必需的 ACT 酰化位点定位在细胞膜上，这些位点在 I 型分泌系统分泌的毒素中是保守的。这些发现揭示了整合素介导附着的结构机制，并解释了抗体介导的 ACT 中毒中和。
