Structural elements influencing von Willebrand factor (vWF) binding
affinity for platelet glycoprotein Ib within a dispase-digested vWF
fragment
S Miura, Y Fujimura, M Sugimoto, T Kawasaki, Y Ikeda, K Titani and A Yoshioka
Department of Pediatrics, Nara Medical College, Japan.
We investigated the structural elements in human von Willebrand factor
(vWF) that influence binding affinity for platelet glycoprotein (GP) Ib
using a dispase-digested vWF fragment as a prototype (residues
Leu480/Val481-Gly718 of the vWF subunit; Andrews et al, Biochemistry
28:8326, 1989). The major structural features of this fragment are a large
A1-loop formed by an intrachain disulfide bond between Cys509 and Cys695
and six O-linked sugar chains. The fragment was chemically modified by (1)
reduction and S-carboxyamido-methylation (R/A), (2) desialylation (DS), or
(3) a combination of both (R/A-DS). The GPIb binding affinity of these
fragments was basically evaluated by competitive binding assay with
anti-GPIb monoclonal antibody (LJ-Ib1), a receptor blocker for vWF
(Sugimoto et al, Biochemistry 30:5202, 1991). Both the prototype and the
R/A fragments were also assessed for their function in shear-induced
platelet aggregation. Results unambiguously demonstrated that the presence
of a disulfide bridge (Cys509-Cys695) within this domain downregulates the
affinity of vWF to GPIb. In addition, it was also demonstrated that the
terminal sialic acids attached to six o-linked sugar chains within this
domain contribute to optimal functional modulation by the antibiotic
ristocetin, but not by snake venom botrocetin.
Volume 84,
Issue 5,
pp. 1553-1558,
09/01/1994
Copyright © 1994 by The American Society of Hematology
