STRUCTURE OF THE COMPLEX OF BOVINE PANCREATIC PHOSPHOLIPASE A(2) WITHA TRANSITION-STATE ANALOG

The 1.89 Angstrom resolution structure of the complex of bovine pancre atic phospholipase A(2) (PLA2) with the transition-state analogue -hep tylphosphonyl-sn-glycero-3-phosphoethanolamine (TSA) has been determin ed. The crystal of the complex is trigonal, space group P3(1)21, a = b = 46.58 and c = 102.91 Angstrom and isomorphous to the native recombi nant wild type (WT). The structure was refined to a final crystallogra phic R value of 18.0% including 957 protein atoms, 88 water molecules, one calcium ion and all 31 non-H atoms of the inhibitor at 1.89 Angst rom resolution. In all, 7726 reflections [F>2 sigma(F)] were used betw een 8.0 and 1.89 Angstrom resolution. The inhibitor is deeply locked i nto the active-site cleft and coordinates to the calcium ion by displa cing the two water molecules in the calcium pentagonal bipyramid by th e anionic O atoms of the phosphate and phosphonate group. The hydroxyl group of Tyr69 hydrogen bonds to the second anionic O atom of the pho sphate group while that of the phosphonate group replaces the third wa ter, 'catalytic' water, which forms a hydrogen bond to N-delta 1 of Hi s48. The fourth water which also shares N-delta 1 of His48 is displace d by the steric hinderance of the inhibitor. The fifth conserved struc tural water is still present in the active site and forms a network of hydrogen bonds with the surrounding residues. The structure is compar ed with the other known TSA-PLA2 complexes. complexes.