Molecular interaction studies of hemostasis: fibrinogen ligand-human platelet receptor interactions

The interactions between fibrinogen ligands and platelet receptor alpha(11b)beta(3) were studied under physiological conditions by atomic force microscopy (AFM). Two linear peptide sequences in fibrinogen, RGD and HHLGGAKQ (A) under bar(G) under bar(D) under barV, play central roles in the regulation of hemostasis and thrombosis by facilitating adhesion and aggregation of platelets. In order to measure the interactions (i.e., debonding force), oligopeptides, GSSSGaaa, where aaa is -(R) under bar(D) under bar(G) under bar SPA or -HHLGGAKQ (A) under bar(G) under bar(D) under barV, were synthesized and grafted on to the surface of AFM probe tips. The interaction forces between a peptide-modified AFM probe tip and platelet surface were determined from pN to nN levels using AFM force measurements. Our results show that the zero kinetic off-rate, K-off(0), for RGDSPA is significantly smaller than that for HHLGGAKQ (A) under bar(G) under bar(D) under barV, under the consideration of flexible receptor surfaces. From our analysis, the K-off(0), the single molecular binding energy E-b, and the transition state x(b), were extracted from the data, and estimated to be 1.53 s(-1), -2.64 x 10(-20) J and 1.03 Angstrom for the RGD-alpha(11b)beta(3) system, and 47.58 s(-1), 2.67 x 10(-20), 1.09 Angstrom for the HHLGGAKQAGDV-alpha(11b)beta(3) system, respectively. (C) 2003 Elsevier Science B.V. All rights reserved.