Structure of the platelet glycoprotein Ib receptor in complex with a novel antithrombotic agent.

Agkisacucetin, a snake C-type lectin-like protein isolated from the venom of Deinagkistrodon acutus (formerly Agkistrodon acutus), is a novel antithrombotic drug candidate in phase 2 clinical trials. Agkisacucetin specifically recognizes the platelet surface receptor glycoprotein Ib α chain (GPIbα) to block GPIb and von Willebrand factor (VWF). In this study, we solved the crystal structure of the GPIbα N-terminal domain (residues 1-305) in complex with agkisacucetin to understand their molecular recognition mechanism. The crystal structure showed that agkisacucetin primarily contacts GPIbα at the C-terminal part of the conserved leucine-rich repeat (LRR) domain (LRR-6 to LRR-8) and the previously described "β-switch" region through the β chain. In addition, we found that agkisacucetin α chain contacts part of the GPIbα C-terminal peptide after the LRR domain through complementary charge interactions. This C-terminal peptide plays a key role in GPIbα and thrombin recognition. Therefore, our structure revealed that agkisacucetin can sterically block the interaction between the GPIb receptor and VWF and thrombin proteins to inhibit platelet function. Our structural work provides key molecular insights into how an antithrombotic drug candidate recognizes the GPIb receptor to modulate platelet function to inhibit thrombosis.