Fibrinogen binds to integrin alpha(5)beta(1) via the carboxyl-terminal RGDsite of the A alpha-chain

Fibrinogen interactions with vascular endothelial cells are implicated in v arious physiological and pathophysiological events, including angiogenesis and wound healing, We have shown previously that integrin alpha(5)beta(1) i s a fibrinogen receptor on endothelial cells [Suehiro, H., Gailit, J., and Plow, E.F. (1997) J. Biol Chem. 272, 5360-5366], In the present study, we h ave characterized fibrinogen interactions with purified alpha(5)beta(1) and have identified the recognition sequence in fibrinogen for alpha(5)beta(1) . The binding of fibrinogen to immobilized alpha(5)beta(1) was selectively supported by Mn2+. Fibrinogen bound to purified alpha(5)beta(1) in a time-d ependent, specific, and saturable manner in the presence of Mn2+, and the b inding was blocked completely by Arg-Gly-Asp (RGD)-containing peptides and by anti-a, and anti-alpha(5)beta(1) monoclonal antibodies. A monoclonal ant ibody directed to the C-terminal RGD sequence at A alpha 572-574 significan tly inhibited the binding of fibrinogen to alpha(5)beta(1), whereas monoclo nal antibodies directed to either the N-terminal RGD sequence at A alpha 95 -97 or the C-terminus of the gamma-chain did not, Furthermore, substituting RGE for RGD at position A alpha 95-97 in recombinant fibrinogen had a mini mal effect on binding, whereas substituting RGE for RGD at position A alpha L572-574 decreased binding by 90%, These results demonstrate that the C-te rminal RGD sequence at A alpha 572-574 is required for the interaction of f ibrinogen with alpha(5)beta(1).