CRYSTAL-STRUCTURE OF HUMAN SECRETORY PHOSPHOLIPASE A(2)-IIA COMPLEX WITH THE POTENT INDOLIZINE INHIBITOR 120-1032

Phospholipase A(2), is a key enzyme in a number of physiologically imp ortant cellular processes including inflammation and transmembrane sig naling, Human secretory phospholipase A(2)-IIA is present at high conc entrations in synovial fluid of patients with rheumatoid arthritis and in the plasma of patients with septic shock, Inhibitors of this enzym e have been suggested to be therapeutically useful non-steroidal anti- inflammatory drugs, The crystal structure of human secretory phospholi pase A(2)-IIA bound to a novel potent indolizine inhibitor (120-1032) has been determined, The complex crystallizes in the space group P3(1) 21, with cell dimensions of a= b =75.8 Angstrom and c =51.3 Angstrom, The model was refined to an R-factor of 0.183 for the intensity data c ollected to a resolution of 2.2 Angstrom, It was revealed that the inh ibitor is located near the active site and bound to the calcium ion, A lthough the binding mode of the 120-1032 inhibitor to human secretory phospholipase A(2)-IIA is similar to that previously determined for an indole inhibitor LY311299, the specific interactions between the enzy me and the inhibitor in the present complex include the oxycarboxylate group which was introduced in this inhibitor, The oxycarboxylate grou p in 120-1032 is coordinated to the calcium ion and included in the wa ter-mediated hydrogen bonding to the catalytic Asp49. In addition, the ethyl group in 120-1032 gains hydrophobic contacts with the cavity wa ll of the hydrophobic channel of the enzyme.