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

The interactions between fibrinogen ligands and platelet receptor αIIbβ3 were studied under physiological conditions by atomic force microscopy (AFM). Two linear peptide sequences in fibrinogen, RGD and HHLGGAKQAGDV, 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 -RGDSPA or -HHLGGAKQAGDV, 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, Koff(0), for RGDSPA is significantly smaller than that for HHLGGAKQAGDV, under the consideration of flexible receptor surfaces. From our analysis, the Koff(0), the single molecular binding energy Eb, and the transition state xb, were extracted from the data, and estimated to be 1.53 s−1, −2.64×10−20 J and 1.03 Å for the RGD–αIIbβ3 system, and 47.58 s−1, 2.67×10−20, 1.09 Å for the HHLGGAKQAGDV–αIIbβ3 system, respectively.