Cellular source of VWF determines its susceptibility for ADAMTS13-mediated proteolysis. VWF produced by endothelial cells (A) is stored in the Weibel-Palade (WP) bodies as a glycoprotein containing N-linked glycans (blue dots) that are sialylated (green triangles). Upon stimulated release, VWF assembles into long strings that are susceptible to proteolysis by ADAMTS13. Unexpectedly, McGrath et al have now found that VWF stored in the α-granules of platelets (B) contains much less sialic acids on the N-linked glycans (blue dots). Moreover, this lack of sialic acids converts VWF into a substrate that is less efficiently proteolyzed by ADAMTS13, providing it with a higher hemostatic potential. Professional illustration by Marie Dauenheimer.