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Updated: Aug 15, 2026

Live-cell Imaging of Platelet Degranulation and Secretion Under Flow
Published on: July 10, 2017
von Willebrand factor but not alpha-thrombin binding to platelet glycoprotein Ibalpha is influenced by the HPA-2
Hans Ulrichts1, Karen Vanhoorelbeke, Sandra Cauwenberghs
1Laboratory for Thrombosis Research, IRC, KULeuven Campus Kortrijk, E. Sabbelaan 53, 8500 Kortrijk, Belgium.
Objective:
Glycoprotein (GP) Ibalpha is the functionally dominant subunit of the platelet GPIb-IX-V receptor complex. The N-terminal domain of the GPIbalpha chain contains binding sites for alpha-thrombin and von Willebrand factor (VWF). The human platelet alloantigen (HPA)-2 polymorphism of the GPIbalpha gene is associated with a C/T transition at nucleotide 1018, resulting in a Thr/Met dimorphism at residue 145 of GPIbalpha. To study the structural and functional effects of this dimorphism, N-terminal fragments (AA1-289) of the HPA-2a and HPA-2b alloform of GPIbalpha expressed in CHO cells were used.
Methods And Results:
Of 74 moAbs directed against human GPIbalpha, 2 antibodies with epitope between AA1-59 could differentiate between both alloforms. In addition, VWF bound with a higher affinity to the recombinant HPA-2a fragment or to homozygous HPA-2a platelets. In contrast, no difference was found in the binding of alpha-thrombin to the recombinant alloform fragments or of antibodies directed against the alpha-thrombin binding anionic sulfated tyrosine sequence (AA269-282).
Conclusions:
Whereas the Thr145Met dimorphism does not affect alpha-thrombin binding, it does influence the conformation of the N-terminal flanking region and first leucine-rich repeat of GPIbalpha and by this has an effect on VWF binding.
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