Haspel J, Schürmann G, Jacob J, Erickson H P, Grumet M
W.M. Keck Center for Collaborative Neuroscience, Rutgers University, Piscataway, New Jersey 08854-8082, USA.
J Neurosci Res. 2001 Nov 1;66(3):347-55. doi: 10.1002/jnr.1227.
The neural cell adhesion molecule L1 contains immunoglobulin-like (Ig) domains in its extracellular region that mediate homophilic binding, neurite outgrowth and other activities relevant to CNS development. To correlate conformations of these domains to biological function, several L1-Fc fusion proteins whose bioactivities were previously characterized were analyzed by rotary shadowing electron microscopy. We found that bioactive L1-Fcs containing Ig domains 1-4 or 1-6 exhibited extended, branched structures. In contrast, inactive L1-Fcs containing only the first two or three Ig domains assumed compact shapes that suggested interactions between the L1 arms of these proteins. Analysis of an untagged L1 fragment composed of Ig domains 1-3 demonstrated a mixture of monomeric and dimeric forms. Surprisingly, these dimers were stabilized by intermolecular disulfide bonds. Finally, cell surface L1-GFP fusion proteins containing only the first two or three Ig domains in the extracellular region also engaged in disulfide-mediated dimerization. These results suggest a novel mechanism by which mutations in L1 could interfere with its biological functioning.
神经细胞黏附分子L1在其细胞外区域含有免疫球蛋白样（Ig）结构域，这些结构域介导同源性结合、神经突生长以及与中枢神经系统发育相关的其他活动。为了将这些结构域的构象与生物学功能相关联，通过旋转阴影电子显微镜对几种先前已表征其生物活性的L1-Fc融合蛋白进行了分析。我们发现，含有Ig结构域1-4或1-6的生物活性L1-Fc呈现出伸展的分支结构。相比之下，仅含有前两个或三个Ig结构域的无活性L1-Fc呈现出紧凑的形状，这表明这些蛋白的L1臂之间存在相互作用。对由Ig结构域1-3组成的无标签L1片段的分析表明存在单体和二聚体形式的混合物。令人惊讶的是，这些二聚体通过分子间二硫键得以稳定。最后，细胞表面L1-GFP融合蛋白在细胞外区域仅含有前两个或三个Ig结构域，它们也参与了二硫键介导的二聚化。这些结果提示了一种新机制，通过该机制L1中的突变可能会干扰其生物学功能。
