Gain of von Willebrand factor-binding function by mutagenesis of a species-conserved residue within the leucine-rich repeat region of platelet glycoprotein Ibα

Abstract

Glycoprotein (GP) Ibα, a member of the leucine-rich repeat (LRR) protein family, mediates platelet adhesion to immobilized von Willebrand factor (VWF). We investigated the role in VWF binding of charged residues in the LRR region of GP Ibα that are conserved in human, canine, and murine proteins. Substitution of His86 with either Ala or Glu resulted in a gain of VWF-binding function as judged by increased VWF binding in the presence of the modulators ristocetin and botrocetin and by enhanced adhesion of Chinese hamster ovary (CHO) cells expressing the mutant GP Ibα to immobilized VWF under conditions of flow. This is the first report of a gain-of-function phenotype resulting from mutations in the LRR region of GP Ibα. Because His86 is 2 nm away from the region of GP Ibα with the largest surface of contact with VWF, the data suggest that the LRRs regulate GP Ibα affinity for VWF allosterically. © 2005 by The American Society of Hematology.