Functional domain structure of fibronectin.

Abstract

Structural domains of fibronectin (FN) and their ability to associate with cell surface components were systematically investigated. Plasma FN was cleaved into 3 structural domains (MW 150,000-140,000, 40,000 and 32,000) by sequential digestion with trypsin and thermolysin. A single digestion with thermolysin alone generated MW 150,000-140,000, 40,000 and smaller fragments. With the inclusion of thermolysin, but not with other proteases, one can, with a high yield, dissect FN simultaneously into 3 clearly distinctive functional domains. Of 3 major fragments, only the MW 40,000 fragment bound to a gelatin column; this fragment contained essentially all of the carbohydrates present in the original FN. Heparin-binding sites were localized on both the MW 150,000-140,000 and 32,000 fragments, but not on the MW 40,000 fragment. Only the MW 150,000-140,000 fragments and intact FN promoted cell spreading, whereas the MW 40,000 and 32,000 fragments could induce cell attachment, but failed to promote cell spreading. FN is apparently composed of (at least) 3 structural domains that are functionally distinct from each other.