Characterization of membrane protein complex associated with dystrophin

在本研究中，我们研究了糖异常复合物在神经系统中的生物学功能。结果表明，神经系统α -肌营养不良聚糖的分子质量为120 kDa，而不是肌肉的15kDa。神经系统α -三磷酸腺苷以高亲和力与层粘连蛋白结合，这种结合依赖于钙，并被肝素和NaCl抑制。神经系统α -糖营养不良被认为与Dp116和肌营养蛋白作为锚定蛋白有关，但与肌聚糖复合物无关。我们还表明，120 kDa α -肌营养不良聚糖是层粘连蛋白-2的雪旺细胞受体，层粘连蛋白-2是层粘连蛋白的神经内膜异构体，由α 2、β 1和γ 1链组成，存在于周围神经系统。雪旺细胞α -三磷酸甘聚糖也是agin的受体，agin是一种乙酰胆碱受体聚集分子，在c端与层粘连蛋白α链部分同源。免疫化学分析表明，agrin的外周神经异构体是神经内膜基底层的400 kDa成分，与周围外周神经纤维髓鞘最外层的α -糖酐共定位。印迹覆盖分析表明，内源性外周神经agrin和laminin-2都能与雪旺细胞α -不良聚糖结合。重组的agrin外周神经异构体的c端片段也能与雪旺细胞α -异糖甘氨酸结合，证实雪旺细胞α -异糖甘氨酸的结合位点位于agrin分子的c端。此外，重组agrin c -末端片段与雪旺细胞α -失调糖聚糖的结合与层粘连蛋白-2的结合竞争。综上所述，这些结果表明-三磷酸腺苷在雪旺细胞膜中是agrin和laminin-2的双重受体。目前，我们正在研究糖异常复合物在中枢神经系统中的生物学功能。

In the present study, we have investigated the biological functions of the dystroglycan complex in the nervous system. As results, we show that the nervous system alpha-dystroglycan has a molecular mass of 120 kDa instead of 15kDa of that of muscle. The nervous system alpha-dystroglycan binds laminin with high affinity and this binding is dependent on calcium and is inhibited by heparin and NaCl. The nervous system alpha-dystroglycan is presumed to be associated with Dp116 and utrophin as anchoring proteins, but not the sarcoglycan complex. We also show that 120 kDa alpha-dystroglycan is a Schwann cell receptor of laminin-2, the endoneurial isoform of laminin comprised of the alpha2, beta1 and gamma1 chains, in the peripheral nervous system. Schwann cellalpha-dystroglycan is also a receptor of agrin, an acetylcholine receptor-aggregating molecule having partial homology to laminin alpha chains in the C-terminus. Immunochemical analysis demonstrates that the peripheral nerve isoform of agrin is a 400 kDa component of the endoneurial basal lamina and is co-localized with alpha-dystroglycan surrounding the outermost layr of myelin sheath of peripheral nerve fibers. Blot overlay analysis demonstrates that both endogenous peripheral nerve agrin and laminin-2 bind to Schwann cell alpha-dystroglycan. Recombinant C-terminal fragment of the peripheral nerve isoform of agrin also binds to Schwann cell alpha-dystroglycan, confirming that the binding site for Schwann cell alpha-dystroglycan resides in the C-terminus of agrinmolecule. Furthermore, the binding of recombinant agrin C-terminal fragment to Schwann cell alpha-dystroglycan competes with that of laminin-2. All together, these results indicate that alpha-dystroglycan is a dual receptor for agrin and laminin-2 in the Schwann cell membrane. Currently, we are investigating the biological functions of the dystroglycan complex in the central nervous system.