N-terminal flanking region of A1 domain in von Willebrand factor stabilizes structure of A1A2A3 complex and modulates platelet activation under shear stress.

ABSTRACT: von Willebrand factor (vWF) mediates platelet adhesion and thrombus formation via its interaction with the platelet receptor glycoprotein (GP)Ib?. We have analyzed two A1A2A3 tri-domain proteins to demonstrate that the amino acid sequence, Gln(1238)-Glu(1260), in the N-terminal flanking region of the A1 domain, together with the association between the A domains, modulates vWF-GPIb? binding and platelet activation under shear stress. Using circular dichroism spectroscopy and differential scanning calorimetry, we have described that sequence Gln(1238)-Glu(1260) stabilizes the structural conformation of the A1A2A3 tri-domain complex. The structural stabilization imparted by this particular region inhibits the binding capacity of the tri-domain protein for GPIb?. Deletion of this region causes a conformational change in the A1 domain that increases binding to GPIb?. Only the truncated protein was capable of effectively blocking ristocetin-induced platelet agglutination. To determine the capacity of activating platelets via the interaction with GPIb?, whole blood was incubated with the N-terminal region truncated or intact tri-A domain protein prior to perfusion over a fibrin(ogen)-coated surface. At a high shear rate of 1,500 s(-1), platelets from blood containing the truncated protein rapidly bound, covering >90% of the fibrin(ogen) surface area, whereas the intact tri-A domain protein induced platelets to bind <10%. The results obtained in this study ascertain the relevant role of the structural association between the N-terminal flanking region of the A1 domain (amino acids Gln(1238)-Glu(1260)) and the A1A2A3 domain complex in preventing vWF to bind spontaneously to GPIb? in solution under high shear forces.

SUBMITTER: Auton M 

PROVIDER: S-EPMC3340263 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature