Mutation in the leucine-rich repeat of platelet glycoprotein Ib alpha results in defects in its interaction with immobilized von Willebrand factor under flow.
OBJECTIVE
To characterize effects of the GP Ib alpha mutation (A156V) on its interaction with von Willebrand factor (vWf) under high fluid shear stress.


METHODS
The residue A156 of GP Ib alpha was converted to a valine and the mutant expressed in CHO cells expressing wild-type GP Ib beta and GPIX. The transfected cells were tested for their interaction with a panel of GP Ib alpha antibodies and for rolling on immobilized vWf under high shear.


RESULTS
The mutation led to surface expression of a GP Ib alpha polypeptide that adopted a different conformation at its N-terminus because binding of the GP Ib alpha antibody AN51, which has a binding epitope in the N-terminal 35 residues, was eliminated, whereas binding of the others (AK2, MB45, and SZ2, all of which bind to regions C-terminal to the AN51 epitope) was normal. Mutant-expressing cells could adhere and roll on immobilized vWf under high fluid shear stress and rolled significantly faster than wild-type cells.


CONCLUSIONS
These studies demonstrate that the mutation A156V results in a conformation change at the N-terminus of GP Ib alpha, which leads to an increase in the dissociation rate of the bond between the GP Ib alpha mutant and vWf.
Dong
J
J
Division of Hematology/Oncology, Department of Internal Medicine, Baylor College of Medicine, Veterans Affairs Medical Center, Houston, TX, USA. jfdong@bcm.tmc.edu
Li
C
C
Schade
A J
AJ
Fredrickson
B J
BJ
Sun
L
L
McIntire
L V
LV
López
J A
JA
D000818:Animals; D016466:CHO Cells; D002448:Cell Adhesion / Q000235:genetics; D002465:Cell Movement / Q000235:genetics; D006224:Cricetinae; D007930:Leucine / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000235:genetics*; D014841:von Willebrand Factor / Q000378:metabolism*
D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor; D007930:Leucine