Erickson H P, Inglesias J L
Nature. 1984;311(5983):267-9. doi: 10.1038/311267a0.
Fibronectins are adhesive glycoproteins thought to mediate the attachment of cells to various substrates. Plasma fibronectin (PFN) is a dimer comprising subunits of molecular weight 220,000, connected by one or two disulphide bonds. Electron microscopy shows that PFN is a long, flexible strand, 2-3 nm in diameter and 140 nm long. Many cells in tissue culture elaborate an extracellular matrix of insoluble (highly cross-linked by disulphide bonds) fibronectin, and a variable amount of 'cell surface fibronectin' (CSFN) that can be extracted by mild urea treatment. This CSFN, soluble in 1 M urea and at high pH, is a mixture of dimers and disulphide-bonded oligomers. In the present study we have examined the structure of these molecules by electron microscopy. Oligomers were separated from dimers and contaminating proteins by zone sedimentation through glycerol gradients. We report that the CSFN dimers are identical in structure to PFN. In contrast, the oligomers have an elaborate and well defined structure that we call a 'hexabrachion': six arms emanating from a central globular particle. The arms are similar to PFN in being long, thin and flexible, but have several distinctly different features.
纤连蛋白是一种黏附性糖蛋白，被认为可介导细胞与各种底物的附着。血浆纤连蛋白（PFN）是一种二聚体，由分子量为220,000的亚基组成，通过一个或两个二硫键相连。电子显微镜显示，PFN是一条长而柔韧的链，直径为2 - 3纳米，长度为140纳米。组织培养中的许多细胞会形成一种不溶性（通过二硫键高度交联）纤连蛋白的细胞外基质，以及可通过温和尿素处理提取的可变数量的“细胞表面纤连蛋白”（CSFN）。这种可溶于1 M尿素和高pH值的CSFN是二聚体和二硫键连接的寡聚体的混合物。在本研究中，我们通过电子显微镜检查了这些分子结构。通过甘油梯度区带沉降将寡聚体与二聚体及污染蛋白分离。我们报告称，CSFN二聚体在结构上与PFN相同。相比之下，寡聚体具有一种精细且明确的结构，我们称之为“六臂体”：从一个中央球状颗粒伸出六条臂。这些臂与PFN相似，长、细且柔韧，但有几个明显不同的特征。
