Crystal structure of receptor-binding C-terminal repeats from Clostridium difficile toxin A
Crystal structure of receptor-binding C-terminal repeats from Clostridium difficile toxin A
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DOI：
10.1073/pnas.0506391102
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发表时间：
2005-12-20
影响因子：
11.1
通讯作者：
Ng, KKS
中科院分区：
文献类型：
--
作者：
Ho, JGS;Greco, A;Ng, KKS
艰难梭菌（Clostridium difficile）是一种主要的医院病原体，它产生两种能够破坏肠上皮细胞的大蛋白毒素[毒素a （TcdA）和毒素B (TcdB)]。两者都属于大型梭状细胞毒素家族，其特征是存在重复的c端重复结构域（CRID）。在TcdA中，CRD由39个重复序列组成，负责与细胞表面碳水化合物结合。为了了解艰难梭菌毒素与细胞结合的分子结构基础，我们确定了艰难梭菌毒素a CRD C端127-aa片段的1.85埃分辨率晶体结构。该结构揭示了包含5个重复的p-螺线管折叠，每个重复由一个β发夹组成，然后是一个由7-10个短重复（SRs）或18个长重复（LRs）残基组成的环。相邻的一对β -发夹以90度或120度的螺旋轴旋转关系相互关联，这取决于相邻β -发夹中关键位置的氨基酸的性质。毒素A和B的完整CRD模型表明，每个CRD都包含由3到5个sr组成的p -螺线管的直线延伸，这些sr由单个LR的存在所引入的扭结打断。这些结构特征为理解大型梭状芽胞杆菌细胞毒素如何与细胞表面结合提供了一个框架，并为通过阻断毒素与细胞表面的结合来开发新的治疗艰难梭状芽胞杆菌相关疾病的方法提供了建议。
Clostridium difficile is a major nosocomial pathogen that produces two large protein toxins [toxin A (TcdA) and toxin B (TcdB)] capable of disrupting intestinal epithelial cells. Both belong to the family of large clostridial cytotoxins, which are characterized by the presence of a repetitive C-terminal repetitive domain (CRID). In TcdA, the CRD is composed of 39 repeats that are responsible for binding to cell surface carbohydrates. To understand the molecular structural basis of cell binding by the toxins from C. difficile, we have determined a 1.85-angstrom resolution crystal structure of a 127-aa fragment from the C terminus of the toxin A CRD. This structure reveals a p-solenoid fold containing five repeats, with each repeat consisting of a beta-hairpin followed by a loop of 7-10 residues in short repeats (SRs) or 18 residues in long repeats (LRs). Adjacent pairs of beta-hairpins are related to each other by either 90 degrees or 120 degrees screw-axis rotational relationships, depending on the nature of the amino acids at key positions in adjacent beta-hairpins. Models of the complete CRDs of toxins A and B suggest that each CRD contains straight stretches of P-solenoid composed of three to five SRs that are punctuated by kinks introduced by the presence of a single LR. These structural features provide a framework for understanding how large clostridial cytotoxins bind to cell surfaces and suggest approaches for developing novel treatments for C. difficile-associated diseases by blocking the binding of toxins to cell surfaces.