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 Wil lebrand factor (vWf) in (patho)physiologic thrombus formation. The vWf-bind ing site on GP Ib-IX-V is within the N-terminal 282 residues of GP Iba, whi ch consist of an N-terminal flanking sequence (His-1-IIe-35), 7 leucine-ric h repeats (Leu-36-Ala-200), a C-terminal flank (Phe-201-Gly-268), and a sul fated tyrosine sequence (Asp-269-Glu-282), We have used mammalian cell expr ession of canine-human chimeras of GP Ib alpha, corresponding to precise st ructural boundaries, to demonstrate the first specific requirement for indi vidual leucine-rich repeats for binding of vWf either induced by a modulato r, ristocetin, or under hydrodynamic flow. implicit in this approach was th at the GP Ib alpha chimeras retained a functional conformation, a suppositi on confirmed by analyzing restoration of function to reversed human-canine chimeras and demonstrating that all chimeras bound vWf activated by botroce tin, a modulator that is indiscriminate between species. Leucine-rich repea ts 2, 3, and 4 of GP Ib alpha were identified as being critical for vWf adh esion to GP Ib-IX-V. (C) 2000 by The American Society of Hematology.