RESUMO
Basic phospholipase A(2) from the venom of Agkistrodon halys Pallas ( Agkistrodin blomhoffii brevicaudus ) exhibits hemolytic and anti-coagulant activities. A new monoclinic crystal form with four molecules per asymmetric unit was grown in the absence of n-octyl beta-o-glucopyranoside (beta-OG). The enzyme structure was determined by the molecular replacement method. The combined analysis of self- and cross- rotation function was used and non-crystallographic symmetry restraints were imposed to the structure refinement. The final model gave an acceptable crystallographic R factor and reasonable stereochemistry. Two molecules formed an interfacial-recognition-site linked dimer and two such dimers constituted a tetramer having pseudo 222 symmetry. Structural comparison with previously reported monoclinic forms, in which beta-OG was bound, showed that the variation of crystallization conditions had effects on the crystal packing, leading to significant changes of the cell parameters. Nevertheless, the structures of both the dimer and tetramer in the two crystal forms closely resembled to each other, indicating that the oligomers found in the monoclinic crystal forms were stable.
