Requirement Of Leucine-Rich Repeats Of Glycoprotein (Gp) Ib Alpha For Shear-Dependent And Static Binding Of Von Willebrand Factor To The Platelet Membrane Gp Ib-Ix-V Complex

The platelet glycoprotein (GP) Ib-IX-V complex mediates adhesion to von Willebrand factor (vWf) in (patho)physiologic thrombus formation. The vWf-binding site on GP Ib-IX-V is within the N-terminal 282 residues of GP Iba, which consist of an N-terminal flanking sequence (His-1-IIe-35), 7 leucine-rich repeats (Leu-36-Ala-200), a C-terminal flank (Phe-201-Gly-268), and a sulfated tyrosine sequence (Asp-269-Glu-282), We have used mammalian cell expression of canine-human chimeras of GP Ib alpha, corresponding to precise structural boundaries, to demonstrate the first specific requirement for individual leucine-rich repeats for binding of vWf either induced by a modulator, ristocetin, or under hydrodynamic flow. implicit in this approach was that the GP Ib alpha chimeras retained a functional conformation, a supposition confirmed by analyzing restoration of function to reversed human-canine chimeras and demonstrating that all chimeras bound vWf activated by botrocetin, a modulator that is indiscriminate between species. Leucine-rich repeats 2, 3, and 4 of GP Ib alpha were identified as being critical for vWf adhesion to GP Ib-IX-V.(C) 2000 by The American Society of Hematology.