Domain structure of the carboxyl-terminal half of human plasma fibronectin.

The organization of domains in the COOH-terminal half of human plasma fibronectin was analyzed after controlled tryptic hydrolysis.In physiological salt so- lutions, fragments from this region interact with fibrin, heparin, and the cell surface, but not with actin, Stuphylococcus aureus, or native DNA.Each of the four major tryptic fragments (designated 7,9,13, and 22) was purified by sequential affinity-and DEAE-column chromatography.The relationships between these fragments were examined by affinity chromatography, sequential tryptic cleavage, and two-dimensional peptide mapping; in addition, cell-spreading activity and content of carbohydrate and free sulfhydryl groups were also determined for each fragment.The apparent relative order of binding sites is cellbinding domain (fragment 13, M, = 75,000); heparinbinding domain (subfragment 20c of fragment 9, M, = 38,000); fibrin-binding domain (fragment 22, Mr = 34,000) for the A chain, and cell-binding domain (fragment 13); heparin-binding domain (NH2-terminal part of subfragment 15 of fragment 7, M, = 58,000), and fibrin-binding domain (COOH-terminal part of subfragment 15) for the B chain.Carbohydrates and a free sulfhydryl group are present in the cell-binding region, and a second free sulihydryl or labile disulfide appears to be present on both chains in the fibrin-binding region.An apparent region of difference between the chains is present between COOH-terminal heparin-and fibrin-binding domains.These studies provide a map of the domains in the COOH-terminal half of fibronectin, and they indicate relatively limited structural and functional differences between the A and B chains of fibronectin.This map and the establishment of purification protocols for fragments spanning this entire region should also be useful in future analyses of fibronectin primary structure.The adhesive glycoprotein fibronectin appears to function in a wide variety of cellular functions, including cell-to-substratum adhesion, cell-to-cell adhesion, ceU migration, cell growth, embryonic differentiation, regulation of cell morphology and alignment, wound healing, and reticuloendothelial clearance of colloidal debris (1-8).These biological activities