ISOLATION AND BIOLOGICAL CHARACTERIZATION OF ACTIVE FRAGMENTS OF THE ADHESIVE GLYCOPROTEIN FIBRONECTIN

Cellular fibronectin is a major cell surface glycoprotein that can mediate the adhesion of cells to collagen in vitro. To analyze its mechanism of action, we have undertaken experiments to isolate fragments of fibroblast fibronectin that retain different active sites. In this paper, we describe the purification of three chymotryptic fragments with apparent molecular weights of 40,000, 160,000 and 205,000 from chicken cellular fibronectin. These fragments were electrophoretically pure and retained different biologically active sites, as determined by a series of bioassays and competitive inhibition experiments. The 40K fragment was identified as the collagen-binding fragment. The 160K fragment was found to contain the cell surface-binding site(s) of cellular fibronectin. The 205K fragment contained both collagen-binding and cell surface-binding sites, and apparently represents the sum of the 40K and 160K fragments. When native fibronectin is cleaved to the 205K fragment, a polypeptide region containing all interchain disulfide bonds is lost. This alteration was accompanied by decreased hemagglutinating activity and loss of the capacity to restore a normal morphology to transformed cells, whereas cell attachment to collagen and cell spreading activities remained. Our results directly support the idea that the fibronectin molecule consists of separate structural domains containing different biological characteristics. © 1979.