Visualization of clustered protocadherin neuronal self-recognition complexes
Visualization of clustered protocadherin neuronal self-recognition complexes
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DOI：
10.1038/s41586-019-1089-3
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发表时间：
2019-05-09
期刊：
影响因子：
64.8
通讯作者：
Shapiro, Lawrence
中科院分区：
文献类型：
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作者：
Brasch, Julia;Goodman, Kerry M.;Shapiro, Lawrence
神经突自我识别和回避是所有神经系统的基本特性（1）。这些过程促进树突树枝化（2，3），防止形成autapses（4），并允许非自我神经元之间的自由互动（1，2，3，4，5）。自我神经突之间的回避是由约60种亚型的α-、β-和γ-成簇的原钙粘蛋白的组合的随机细胞表面表达介导的，所述原钙粘蛋白为哺乳动物神经元提供单细胞身份（1，2，4 -13）。在表达相同原钙粘蛋白库的神经元之间观察到回避（2，5），并且单一同种型差异足以阻止自我识别（10）。原钙粘蛋白形成同种型混杂顺式二聚体和同种型特异性亲同反式二聚体（10，14 -20）。尽管这些相互作用先前已经被单独表征（15，17 -20），全长原钙粘蛋白胞外域的结构尚未确定，并且这两个界面如何参与神经元表面之间的自我识别仍然未知。在这里，我们确定的分子排列的全长成簇的原钙粘蛋白胞外域在单一异构体的自我识别复合物，使用X射线晶体学和冷冻电子断层扫描。我们确定的簇原钙粘蛋白，γ B4胞外域，这揭示了一个拉链样的晶格，是由交替的顺式和反式相互作用形成的晶体结构。使用冷冻电子断层扫描，我们表明，成簇的原钙粘蛋白γ B6胞外结构域拴系到脂质体自发组装成线性阵列在膜接触点，在一个配置，这是一致的组装中观察到的晶体结构。这些线性组件作为平行阵列彼此挤压，以在膜之间形成更大的二维结构。我们的研究结果表明，通过成簇的原钙粘蛋白形成有序的线性组装体代表了神经元回避中的初始自我识别步骤，从而为原钙粘蛋白介导的自我识别的异构体-错配链-终止模型提供了支持，该模型依赖于这些线性链（11）。
Neurite self-recognition and avoidance are fundamental properties of all nervous systems(1). These processes facilitate dendritic arborization(2,3), prevent formation of autapses(4) and allow free interaction among non-self neurons(1,2,3,4,5). Avoidance among self neurites is mediated by stochastic cell-surface expression of combinations of about 60 isoforms of alpha-, beta- and gamma-clustered protocadherin that provide mammalian neurons with single-cell identities(1,2,4-13). Avoidance is observed between neurons that express identical protocadherin repertoires(2,5), and single-isoform differences are sufficient to prevent self-recognition(10). Protocadherins form isoform-promiscuous cis dimers and isoform-specific homophilic trans dimersi (10,14-20) Although these interactions have previously been characterized in isolation(15,17-20), structures of full-length protocadherin ectodomains have not been determined, and how these two interfaces engage in self-recognition between neuronal surfaces remains unknown. Here we determine the molecular arrangement of full-length clustered protocadherin ectodomains in single-isoform self-recognition complexes, using X-ray crystallography and cryo-electron tomography. We determine the crystal structure of the clustered protocadherin , gamma B4 ectodomain, which reveals a zipper-like lattice that is formed by alternating cis and trans interactions. Using cryo-electron tomography, we show that clustered protocadherin gamma B6 ectodomains tethered to liposomes spontaneously assemble into linear arrays at membrane contact sites, in a configuration that is consistent with the assembly observed in the crystal structure. These linear assemblies pack against each other as parallel arrays to form larger two-dimensional structures between membranes. Our results suggest that the formation of ordered linear assemblies by clustered protocadherins represents the initial self-recognition step in neuronal avoidance, and thus provide support for the isoform-mismatch chain-termination model of protocadherin-mediated self-recognition, which depends on these linear chains(11).