48 research outputs found
Shear-Induced Unfolding Activates von Willebrand Factor A2 Domain for Proteolysis
To avoid pathological platelet aggregation by von Willebrand factor (VWF),
VWF multimers are regulated in size and reactivity for adhesion by
ADAMTS13-mediated proteolysis in a shear flow dependent manner. We examined if
tensile stress in VWF under shear flow activates the VWF A2 domain for cleavage
by ADAMTS13 using molecular dynamics simulations. We indeed observed stepwise
unfolding of A2 and exposure of its deeply buried ADAMTS13 cleavage site.
Interestingly, disulfide bonds in the adjacent and highly homologous VWF A1 and
A3 domains obstruct their mechanical unfolding. We generated a full length
mutant VWF featuring a homologous disulfide bond in A2 (N1493C and C1670S), in
an attempt to lock A2 against unfolding. We find this mutant to feature
ADAMTS13-resistant behavior in vitro. Our results yield molecular-detail
evidence for the force-sensoring function of VWF A2, by revealing how tension
in VWF due to shear flow selectively exposes the A2 proteolysis site to
ADAMTS13 for cleavage while keeping the folded remainder of A2 intact and
functional. We find the unconventional knotted Rossman fold of A2 to be the key
to this mechanical response, tailored for regulating VWF size and activity.
Based on our model we can explain the pathomechanism of some natural mutations
in the VWF A2 domain that significantly increase the cleavage by ADAMTS13
without shearing or chemical denaturation, and provide with the
cleavage-activated A2 conformation a structural basis for the design of
inhibitors for VWF type 2 diseases