1.72 A resolution refinement of the trigonal form of bovine pancreatic phospholipase A2.

The trigonal crystal structure of the recombinant bovine pancreatic phospholipase A2 has been re-refined at a slightly higher resolution (1.72 A). The crystals are trigonal, space group P3121, unit-cell parameters a = b = 46.78 and c = 102.89 A and are isomorphous to the previous structure. The structure was refined to a final crystallographic R value of 19.5% (Rfree = 28.4%) using 10 531 reflections. A total of 106 solvent molecules were included in the refinement compared with the earlier refinement which contains only 85 water molecules and 8 925 reflections at 1.8 A resolution. The root-mean-square deviation from the ideal bond lengths and bond angles is considerably better in the present refinement. The active site is extended ( approximately 14 A) from Ala1 to the calcium. The three catalytic residues (Asp99, His48 and the catalytic water) are connected by the conserved structural water and the N-terminal Ala1 on one side, and by the calcium through an equatorial water on the other. The water molecules play a role in the activity of the enzyme PLA2. The Ala1 end of the extended active site performs the activation of the phospholid membranes while the opposite end performs the hydrolysis of the monomeric phospholids.