Department of Biochemistry and Molecular Biophysics, Columbia University, New York, United States.
Department of Systems Biology, Columbia University, New York, United States.
Elife. 2016 Oct 26;5:e20930. doi: 10.7554/eLife.20930.
Stochastic cell-surface expression of α-, β-, and γ-clustered protocadherins (Pcdhs) provides vertebrate neurons with single-cell identities that underlie neuronal self-recognition. Here we report crystal structures of ectodomain fragments comprising cell-cell recognition regions of mouse γ-Pcdhs γA1, γA8, γB2, and γB7 revealing -homodimers, and of C-terminal ectodomain fragments from γ-Pcdhs γA4 and γB2, which depict -interacting regions in monomeric form. Together these structures span the entire γ-Pcdh ectodomain. The -dimer structures reveal determinants of γ-Pcdh isoform-specific homophilic recognition. We identified and structurally mapped -dimerization mutations to the C-terminal ectodomain structures. Biophysical studies showed that Pcdh ectodomains from γB-subfamily isoforms formed dimers, whereas γA isoforms did not, but both γA and γB isoforms could interact in with α-Pcdhs. Together, these data show how interaction specificity is distributed over all domains of the γ-Pcdh interface, and suggest that subfamily- or isoform-specific -interactions may play a role in the Pcdh-mediated neuronal self-recognition code.
随机的细胞表面α-、β-和γ-聚类原钙粘蛋白（Pcdh）的表达为脊椎动物神经元提供了单细胞身份，这是神经元自我识别的基础。在这里，我们报告了包含小鼠γ-Pcdh γA1、γA8、γB2 和 γB7 的细胞间识别区域的外域片段的晶体结构，揭示了同源二聚体，以及γ-Pcdh γA4 和 γB2 的 C 端外域片段，其以单体形式描绘了相互作用区域。这些结构共同跨越了整个γ-Pcdh 外域。-二聚体结构揭示了γ-Pcdh 同工型特异性同亲识别的决定因素。我们确定并在结构上对 C 端外域结构进行了 -二聚化突变。生物物理研究表明，γB 亚家族同工型的 Pcdh 外域形成二聚体，而 γA 同工型则不能，但 γA 和 γB 同工型都可以与α-Pcdh 相互作用。总之，这些数据表明了相互作用特异性是如何分布在γ-Pcdh 界面的所有结构域上的，并表明亚家族或同工型特异性 -相互作用可能在 Pcdh 介导的神经元自我识别代码中发挥作用。
