Drescher B, Spiess E, Schachner M, Probstmeier R
Molekulare Biophysik 1, Deutsches Krebsforschungszentrum, Heidelberg, Germany.
Eur J Neurosci. 1996 Dec;8(12):2467-78. doi: 10.1111/j.1460-9568.1996.tb01541.x.
In the present study we have analysed the morphology of two fragments with apparent molecular weights of 180 and 140 kDA (L1-180 and L1-140) derived from the extracellular region of the murine neural cell adhesion molecule L1. The fragment L1-180 consists of almost the entire extracellular part of the molecule, and is built up of six immunoglobulin-like and five fibronectin type III-like domains. Fragment L1-140 lacks one-half of the third, the fourth and the fifth fibronectin type III-like domains. By electron microscopic analysis of rotary-shadowed molecules, L1-140 and L1-180 revealed fibrillar structures 31-43 nm long and 7-12 nm wide with one pronounced globular terminal domain. As determined by complex formation with an L1 antibody, this terminal part of the molecule is formed by the fibronectin type III-like domains. The individual structures showed variation and complexity, and four distinct aspects were identified. These different forms probably represent two-dimensional projections of the same three-dimensional helical structure. Computer-assisted modelling of the L1 molecule, i.e. the protein backbone, showed no strong intramolecular interaction between the different fibronectin type III- or Ig-like domains, suggesting that the formation of the globular part of the molecule is probably achieved by protein-carbohydrate and/or carbohydrate-carbohydrates rather than protein-protein interactions. In addition, our model proposes that interactions occur within the interfaces between the different domains. The highly conserved amino acid residues in these regions point to the necessity of maintaining the orientation between the different domains.
在本研究中，我们分析了源自小鼠神经细胞粘附分子L1细胞外区域的两个片段的形态，其表观分子量分别为180 kDa和140 kDa（L1 - 180和L1 - 140）。片段L1 - 180几乎由该分子的整个细胞外部分组成，由六个免疫球蛋白样结构域和五个纤连蛋白III型样结构域构成。片段L1 - 140缺少第三个、第四个和第五个纤连蛋白III型样结构域的一半。通过对旋转阴影分子的电子显微镜分析，L1 - 140和L1 - 180显示出长度为31 - 43 nm、宽度为7 - 12 nm的纤维状结构，带有一个明显的球状末端结构域。通过与L1抗体形成复合物确定，该分子的这个末端部分由纤连蛋白III型样结构域形成。各个结构显示出变异和复杂性，并且鉴定出四个不同的方面。这些不同形式可能代表同一三维螺旋结构的二维投影。对L1分子即蛋白质主链进行计算机辅助建模显示，不同的纤连蛋白III型或免疫球蛋白样结构域之间没有强烈的分子内相互作用，这表明该分子球状部分的形成可能是通过蛋白质 - 碳水化合物和/或碳水化合物 - 碳水化合物相互作用，而不是蛋白质 - 蛋白质相互作用。此外，我们的模型提出，不同结构域之间的界面会发生相互作用。这些区域中高度保守的氨基酸残基表明维持不同结构域之间取向的必要性。
