Laboratory of Experimental Morphology, Institute of Anatomy, University of Bern, CH-3000 Bern 9, Switzerland.
Proc Natl Acad Sci U S A. 2013 Jun 25;110(26):10622-7. doi: 10.1073/pnas.1301277110. Epub 2013 Jun 10.
The scaffolding protein at the neuromuscular junction, rapsyn, enables clustering of nicotinic acetylcholine receptors in high concentration and is critical for muscle function. Patients with insufficient receptor clustering suffer from muscle weakness. However, the detailed organization of the receptor-rapsyn network is poorly understood: it is unclear whether rapsyn first forms a wide meshwork to which receptors can subsequently dock or whether it only forms short bridges linking receptors together to make a large cluster. Furthermore, the number of rapsyn-binding sites per receptor (a heteropentamer) has been controversial. Here, we show by cryoelectron tomography and subtomogram averaging of Torpedo postsynaptic membrane that receptors are connected by up to three rapsyn bridges, the minimum number required to form a 2D network. Half of the receptors belong to rapsyn-connected groups comprising between two and fourteen receptors. Our results provide a structural basis for explaining the stability and low diffusion of receptors within clusters.
神经肌肉接头的支架蛋白 rapsyn 使烟碱型乙酰胆碱受体在高浓度下聚集，这对于肌肉功能至关重要。受体聚集不足的患者会出现肌肉无力。然而，受体 - rapsyn 网络的详细组织尚不清楚：不清楚 rapsyn 是首先形成一个宽网，随后受体可以停靠在该网上，还是它仅形成短桥将受体连接在一起以形成大簇。此外，每个受体（异五聚体）的 rapsyn 结合位点的数量一直存在争议。在这里，我们通过冷冻电子断层扫描和 Torpedo 突触后膜的亚图平均化显示，受体之间最多可以通过三个 rapsyn 桥连接，这是形成 2D 网络所需的最小数量。一半的受体属于 rapsyn 连接的群组，包含 2 到 14 个受体。我们的结果为解释受体在簇内的稳定性和低扩散提供了结构基础。
