Crystallization and preliminary diffraction data of a platelet-aggregation inhibitor from the venom of Agkistrodon piscivorus piscivorus (North American water moccasin).

Applaggin (Agkistrodon piscivorus piscivorus platelet-aggregation inhibitor) is a potent inhibitor of blood platelet aggregation derived from the venom of the North American water moccasin. The protein consists of 71 amino acids, is rich in cysteines, contains the sequence-recognition site of adhesion proteins at positions 50-52 (Arg-Gly-Asp) and shares high sequence homology with other snake-venom disintegrins such as echistatin, kistrin and trigramin. Single crystals of applaggin have been grown and X-ray diffraction data have been collected to a resolution of 3.2 A. The crystals belong to space group P4(1)2(1)2 (or its enantiomorph), with unit-cell dimensions a = b = 63.35, c = 74.18 A and two molecules per asymmetric unit. Molecular replacement using models constructed from the NMR structures of echistatin and kistrin has not been successful in producing a trial structure for applaggin.