Structure of Fibronectin and Its Fragments in Electron Microscopy

Abstract

Human plasma fibronectin and a series of its large proteolytic fragments were analyzed by EM using tungsten shadowing on C and polystyrene films. On C, intact fibronectin appeared as a randomly coiled strand; on polystyrene it appeared as an elongated structure. Two fragments of fibronectin, MW = 205,000 and 190,000, which lack the NH2-terminal domain of fibronectin and retain the collagen-binding, cell-attachment and heparin-binding functions, and a MW = 170,000 fragment, which retains the collagen-binding and cell-attachment functions, were seen as rods with varying degrees of nodularity while a MW = 100,000 fragment, which only binds to collagen, had 2 clear-cut domains. The segregation of the functional activities in the fibronectin molecule apparently is based on distinct structural domains, and the existence of an additional structural domain not revealed by biochemical and functional studies is suggested.