1.72 ANGSTROM RESOLUTION REFINEMENT OF THE TRIGONAL FORM OF BOVINE PANCREATIC PHOSPHOLIPASE A(2)

The trigonal crystal structure of the recombinant bovine pancreatic ph ospholipase A(2) has been re-refined at a slightly higher resolution ( 1.72 Angstrom). The crystals are trigonal, space group P3(1)21, unit-c ell parameters a = b = 46.78 and c = 102.89 Angstrom and are isomorpho us to the previous structure. The structure was refined to a final cry stallographic R value of 19.5% (R-free = 28.4%) using 10 531 reflectio ns. A total of 106 solvent molecules were included in the refinement c ompared with the earlier refinement which contains only 85 water molec ules and 8 925 reflections at 1.8 Angstrom resolution. The root-mean-s quare deviation from the ideal bond lengths and bond angles is conside rably better in the present refinement. The active site is extended (s imilar to 14 Angstrom) from Ala1 to the calcium. The three catalytic r esidues (Asp99, His48 and the catalytic water) are connected by the co nserved structural water and the N-terminal Ala1 on one side, and by t he calcium through an equatorial water on the other. The water molecul es play a role in the activity of the enzyme PLA2. The Ala1 end of the extended active site performs the activation of the phospholipid memb ranes while the opposite end performs the hydrolysis of the monomeric phospholipids.