Studies on the Essential Intramolecular Interaction Between the A1 and A2 Domains of von Willebrand Factor
Zoi Karoulia, George Papadopoulos, Michail Nomikos, Angelos Thanassoulas, Theodora Choli Papadopoulou, George Nounessis, Maria Kontou, Constantinos Stathopoulos and Demetres D. Leonidas
Haemostasis depends on the balanced participation of von Willebrand factor (vWF), a large multimeric and
multidomain glycoprotein with essential role during the initial steps of blood clotting. Mature vWF circulates in plasma
with the form of multimers comprised of several domains with diverse functions. More specifically, the A1 domain of
vWF plays crucial role in haemostasis, regulating the mechanism of platelet adhesion in sites of vascular injury while A2
domain regulates the normal turnover of vWF. Recent studies have implied that an intramolecular interaction between A1
and A2 domains exists, which prevents platelets adhesion and subsequently inhibits the initial step of the blood coagulation
mechanism. In an effort to elucidate the essential nature of the interaction between these two domains, we produced
and purified the corresponding recombinant unmodified polypeptides. The secondary structure of the two domains was
studied individually and as a mixture using circular dichroism spectroscopy. The observed interaction was verified by
ELISA competition assays using antibodies and their ability to form productive interactions was further characterized kinetically.
In silico analysis (docking and molecular dynamics simulations) of the A1-A2 binding indicated three possible
structural models highlighting the crucial, for this interaction, region.
von Willebrand factor, A1-A2 domain interaction, Circular Dichroism spectroscopy, Molecular Dynamics simulations
Department of Biochemistry and Biotechnology, University of Thessaly, 26 Ploutonos Str. 41221 Larissa, Greece