Structure of an acidic phospholipase A₂ from the venom of Deinagkistrodon acutus

An acidic phospholipase A₂ was purified from Dein­agkistrodon acutus (Agkistrodon acutus) which displays an inhibitory effect on platelet aggregation. The three-dimensional structure of the enzyme was determined by molecular replacement at 2.6 Å resolution with a crystallographic R factor of 18.40% (R_free = 22.50%) and reasonable stereochemistry. Two molecules in the asymmetric unit form a dimer and the dimer formation accompanies a significant conformational adaptation of segment 14-23, a constituent of the `interface recognition site' (IRS). This probably reflects the inherent structural flexibility of the IRS. The possible expansion of the site for inhibiting platelet aggregation as proposed previously [Wang et al. (1996), J. Mol. Biol. 255, 669-­676] is discussed.