Anticoagulation factor I, a snaclec (snake C-type lectin) from Agkistrodon acutus venom binds to FIX as well as FX: Ca2+ induced binding data

► ACF I inhibits both intrinsic and extrinsic coagulation pathways, but does not inhibit thrombin activity. ► ACF I binds FIX in a Ca2+-dependent manner and the maximal binding between ACF I and FIX occurs at 0.25 mM Ca2+. ► Ca2+ functions as a switch for the binding between ACF I and FIX. ► ACF I has been identified as a FIX and FX binding protein with a higher binding-affinity to FIX than to FX. ► The binding of ACF I with FIX plays a dominant role in the anticoagulation of ACF I in vivo.