Force measurements on the molecular interactions between ligand (RGD) and human platelet αIIb β3 receptor system

The peptide sequence arginine-glycine-aspartate (RGD) found in fibrinogen, von Willebrand factor, fibronectin, and vitronectin, plays a critical role in platelet adhesion and thrombus formation. when bound to the platelet alpha (IIb)beta (3) integrin receptor. Using atomic force microscopy (AFM), we have measured the debonding interaction between an RGD peptide-modified AFM probe tip and a human platelet surface from pN to nN levels of force. The peptide sequence, GSSSGRGDSPA, which contains the biologically active RGDSP sequence with a hydrophilic spacer sequence (GSSSG). was covalently coupled to AFM probe tips. Direct measurements on the debonding force for the RGD ligand - alpha (IIb)beta (3) platelet receptor system were carried out in Tyrode buffer at room temperature. Our results show three distinct distributions of debonding forces at a loading rate of 12 nN/s, from which we estimate the debonding force for the single ligand-receptor to be similar to 93 pN. The results also show evidence for considerable extension in the flexible sample surface during the debonding process, and a linear correlation between the debonding force and the logarithm of the rate of loading. From our analysis, the zero kinetic off-rate K-off(0), the single molecular binding energy Eb, and the transition state x(B), assuming rigid binding, were extracted from the data, and estimated to be 22.6 s(-1), -2.64 x 10(-20) J and 0.1 nm, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.