Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
Proc Natl Acad Sci U S A. 2012 Jan 17;109(3):E127-34. doi: 10.1073/pnas.1117538108. Epub 2011 Dec 14.
Vertebrate classical cadherins mediate selective calcium-dependent cell adhesion by mechanisms now understood at the atomic level. However, structures and adhesion mechanisms of cadherins from invertebrates, which are highly divergent yet function in similar roles, remain unknown. Here we present crystal structures of three- and four-tandem extracellular cadherin (EC) domain segments from Drosophila N-cadherin (DN-cadherin), each including the predicted N-terminal EC1 domain (denoted EC1') of the mature protein. While the linker regions for the EC1'-EC2' and EC3'-EC4' pairs display binding of three Ca(2+) ions similar to that of vertebrate cadherins, domains EC2' and EC3' are joined in a "kinked" orientation by a previously uncharacterized Ca(2+)-free linker. Biophysical analysis demonstrates that a construct containing the predicted N-terminal nine EC domains of DN-cadherin forms homodimers with affinity similar to vertebrate classical cadherins, whereas deleting the ninth EC domain ablates dimerization. These results suggest that, unlike their vertebrate counterparts, invertebrate cadherins may utilize multiple EC domains to form intercellular adhesive bonds. Sequence analysis reveals that similar Ca(2+)-free linkers are widely distributed in the ectodomains of both vertebrate and invertebrate cadherins.
脊椎动物经典钙黏蛋白通过目前在原子水平上理解的机制介导选择性的、依赖钙的细胞黏附。然而，结构和黏附机制的无脊椎动物钙黏蛋白，高度分化，但功能相似，仍然未知。这里我们展示了三个和四个串联的果蝇 N-钙黏蛋白（DN-cadherin）的细胞外钙黏蛋白（EC）结构域片段的晶体结构，每个都包括成熟蛋白的预测 N 端 EC1 结构域（表示为 EC1'）。虽然 EC1'-EC2'和 EC3'-EC4'对的连接区显示与脊椎动物钙黏蛋白相似的三个 Ca2+ 离子结合，但 EC2'和 EC3'结构域通过以前未表征的无 Ca2+连接区以“扭曲”的方向连接。生物物理分析表明，含有 DN-cadherin 预测的 N 端九个 EC 结构域的构建体形成同源二聚体，亲和力类似于脊椎动物经典钙黏蛋白，而删除第九个 EC 结构域则使二聚体化消失。这些结果表明，与脊椎动物钙黏蛋白不同，无脊椎动物钙黏蛋白可能利用多个 EC 结构域形成细胞间的黏附键。序列分析表明，类似的无 Ca2+连接区广泛分布在脊椎动物和无脊椎动物钙黏蛋白的细胞外结构域中。
