The diagram illustrates how platelets may interact with a collagen surface either directly, through GPVI, or indirectly, through von Willebrand factor (VWF). Interaction between collagen and platelet integrin α₂β₁ is not illustrated here. CTRP-1 blocks the activation of platelets by collagen through multiple mechanisms. CTRP-1 binds directly to abundant high-affinity, but uncharacterized, regions of collagen (depicted as blue rectangles) but also binds with lower affinity to sites that overlap with GPVI binding sites in collagen (depicted as tan rectangles). This disruption of GPVI-collagen interaction may partially explain the inhibitory action of CTRP-1. In addition, however, CTRP-1 disrupts VWF binding to collagen, by binding to the VWF A3 domain responsible for the collagen interaction. CTRP-1, therefore, interferes with collagen-induced platelet activation through several protein-protein interactions. The structure of CTRP-1 monomer is shown in the inset.