SOLUTION STRUCTURE OF PORCINE PANCREATIC PHOSPHOLIPASE A(2)

The lipolytic enzyme phospholipase A(2) (PLA(2)) is involved in the de gradation of high-molecular weight phospholipid aggregates in vivo. Th e enzyme has very high catalytic activities on aggregated substrates c ompared with monomeric substrates, a phenomenon called interfacial act ivation, Crystal structures of PLA(2)s in the absence and presence of inhibitors are identical, from which it has been concluded that enzyma tic conformational changes do not play a role in the mechanism of inte rfacial activation, The high-resolution NMR structure of porcine pancr eatic PLA(2) free in solution was determined with heteronuclear multid imensional NMR methodology using doubly labeled C-13,N-15-labeled prot ein. The solution structure of PLA(2) shows important deviations from the crystal structure, In the NMR structure the Ala1 alpha-amino group is disordered and the hydrogen bonding network involving the N-termin us and the active site is incomplete, The disorder observed for the N- terminal region of PLA(2) in the solution structure could be related t o the low activity of the enzyme towards monomeric substrates. The NMR structure of PLA(2) suggests, in contrast to the crystallographic wor k, that conformational changes do play a role in the interfacial activ ation of this enzyme.