Molecular modeling of the seven tandem leucine-rich repeats within the ligand-binding region of platelet glycoprotein Ibα

Platelet glycoprotein (GP)Ib-IX-V mediates von Willebrand Factor (vWF)-dependent adhesion to vascular subendothelium at high shear in (patho)physiological thrombus formation. The ligand-binding domain of GPIb-IX-V is within the N-terminal 282 residues of GPIbα, that contains seven tandem leucine-rich repeats (Leu36-Ala200). Repeats 2-4 are critical for vWF binding. In this study, we have built molecular models of the seven leucine-rich repeats of human, canine and mouse GPIbα, providing novel insights into the species-specific interaction between human vWF and its receptor. Interestingly, a major difference between the models was a large negatively charged patch on the concave face of human, but not canine, repeats 2-4. In addition, five individual mutations within the leucine-rich repeats of GPIbα associated with the bleeding disorder Bernard-Soulier syndrome, that results in dysfunctional vWF binding, were mapped to the model of human GPIbα. This provides the basis for relating these genetic lesions to abnormal function of the receptor.