Skirball Institute of Biomolecular Medicine, Department of Cell Biology, New York University School of Medicine, New York, New York, USA.
Biophys J. 2011 Nov 16;101(10):2341-50. doi: 10.1016/j.bpj.2011.09.050. Epub 2011 Nov 15.
Erythrocytes possess a spectrin-based cytoskeleton that provides elasticity and mechanical stability necessary to survive the shear forces within the microvasculature. The architecture of this membrane skeleton and the nature of its intermolecular contacts determine the mechanical properties of the skeleton and confer the characteristic biconcave shape of red cells. We have used cryo-electron tomography to evaluate the three-dimensional topology in intact, unexpanded membrane skeletons from mouse erythrocytes frozen in physiological buffer. The tomograms reveal a complex network of spectrin filaments converging at actin-based nodes and a gradual decrease in both the density and the thickness of the network from the center to the edge of the cell. The average contour length of spectrin filaments connecting junctional complexes is 46 ± 15 nm, indicating that the spectrin heterotetramer in the native membrane skeleton is a fraction of its fully extended length (∼190 nm). Higher-order oligomers of spectrin were prevalent, with hexamers and octamers seen between virtually every junctional complex in the network. Based on comparisons with expanded skeletons, we propose that the oligomeric state of spectrin is in a dynamic equilibrium that facilitates remodeling of the network as the cell changes shape in response to shear stress.
红细胞具有基于血影蛋白的细胞骨架，为了在微血管内的剪切力下存活，该细胞骨架提供了必要的弹性和机械稳定性。这种膜骨架的结构及其分子间相互作用的性质决定了骨架的机械性能，并赋予了红细胞双凹形的特征形状。我们使用冷冻电子断层扫描技术评估了在生理缓冲液中冷冻的小鼠红细胞完整的、未扩展的膜骨架的三维拓扑结构。断层扫描图像显示，肌动蛋白为基础的节点处有一个复杂的血影蛋白丝网络汇聚，并且从细胞中心到边缘，网络的密度和厚度逐渐降低。连接连接复合体的血影蛋白丝的平均轮廓长度为 46 ± 15nm，表明在天然膜骨架中，血影蛋白异四聚体是其完全展开长度（约 190nm）的一部分。血影蛋白的高级寡聚物很常见，在网络中的几乎每个连接复合体之间都可以看到六聚体和八聚体。基于与扩展骨架的比较，我们提出血影蛋白的寡聚状态处于动态平衡中，这有助于在细胞响应剪切力改变形状时重塑网络。
