Crystal Structure of Ca(2+) Ion-saturated Acidic Phospholipase A(2) From Agkistrodon halys Pallas

The Ca(2+) ion is a cofactor for the catalysis of phospholipase A(2). The crystals of Ca(2+)-saturated acidic phospholipase A(2) from Agkistrodon halys Pallas were obtained by adding CaCl(2) during the crystallization to ensure the complete binding of Ca(2+). The synchrotron diffraction data were collected at 1.6 Aring; resolution. The structure was determined by difference Fouriers methods. The refined structure of Ca(2+)-saturated acidicPLA(2) resembles closely that of the native acidicPLA(2) with, however, some small conformational differences in the Ca(2+)-binding site and the C-terminal loop. The pentagonal bipyramidal configuration consisting of seven oxygen ligands of Ca(2+) ion appears more regular than that of the native acidicPLA(2). The small conformational changes induced by Ca(2+) implies that the main role of Ca(2+) ion is to stabilize the oxyanion in the tetrahedral intermediate formed during the catalysis by electrophilic interaction.