Anticoagulant protein which binds to the gamma-carboxyglutamic acid-domain regions of factors IX (F9) and factor X (F10) in the presence of calcium with a 1 to 1 stoichiometry. Heterodimer of subunits A and B2; disulfide-linked. Expressed by the venom gland. Calcium is required for ligand binding. Belongs to the snaclec family.