Perret E, Leung A, Feracci H, Evans E
Compartimentation et Dynamiques Cellulaires, Unité Mixte de Recherche 144, Centre National de la Recherche Scientifique-Institut Curie, 75248 Paris, France.
Proc Natl Acad Sci U S A. 2004 Nov 23;101(47):16472-7. doi: 10.1073/pnas.0402085101. Epub 2004 Nov 16.
Classical cadherins are primary mediators of calcium-dependent cell interactions in multicellular organisms. Organized in five tandemly repeated E-cadherin (EC) modules, the extracellular segments of these membrane-spanning glycoproteins interact homophilically between opposing cells to create highly regulated patterns of attachment stabilized by cytoskeletal elements inside the cells. Despite many structural and functional studies, a significant controversy exists in regard to the organization of cadherin binding in adhesion sites. Supported by considerable evidence, perhaps the most widely held view is that opposing N-terminal EC1-EC2 (EC12) domains form a "zipper" of bonds. However, immobilized on two atomically smooth surfaces and pushed to adhesive contact, opposing cadherins become fully interdigitated and unbind through three discrete jumps comparable with domain dimensions when pulled apart. So the question remains as to whether mechanical adhesion strength emanates solely from interactions between the peripheral N-terminal domains or involves multiple overlapping domains. It is also unclear whether a primary adhesion complex is formed by a single opposing pair of cadherins or whether the complex involves a more complicated network of cis-bonded multimers. To address these questions, we used a special jump/ramp mode of force spectroscopy to test isolated pairwise interactions between recombinant fragments of ECs. Besides the formation of strong trans-bonded dimers, we find a remarkable hierarchy of rupture strengths for bonds between the full five-domain fragments that suggests multiple mechanical functions for cadherins, perhaps providing distinct properties needed for transient-specific recognition as well as stable tissue formation.
经典钙黏着蛋白是多细胞生物中钙依赖性细胞相互作用的主要介质。这些跨膜糖蛋白的细胞外区段由五个串联重复的E-钙黏着蛋白（EC）模块组成，在相对的细胞之间进行同嗜性相互作用，以形成由细胞内细胞骨架元件稳定的高度调控的附着模式。尽管进行了许多结构和功能研究，但关于钙黏着蛋白在黏附位点的结合组织仍存在重大争议。有大量证据支持，也许最普遍的观点是相对的N端EC1-EC2（EC12）结构域形成一个“拉链”状的键。然而，当固定在两个原子光滑的表面上并被迫进行黏附接触时，相对的钙黏着蛋白会完全相互交错，并且在拉开时通过与结构域尺寸相当的三个离散跳跃而解离。因此，问题仍然存在，即机械黏附强度是否仅源于外周N端结构域之间的相互作用，还是涉及多个重叠结构域。同样不清楚的是，主要黏附复合物是由一对相对的钙黏着蛋白形成的，还是该复合物涉及更复杂的顺式结合多聚体网络。为了解决这些问题，我们使用了一种特殊的跳变/斜坡力谱模式来测试EC重组片段之间的孤立成对相互作用。除了形成强的反式结合二聚体之外，我们还发现完整的五结构域片段之间的键的断裂强度存在显著的层次结构，这表明钙黏着蛋白具有多种机械功能，可能为瞬时特异性识别以及稳定的组织形成提供所需的不同特性。
