MOLECULAR-MODEL OF THE INTERACTION OF BEE VENOM PHOSPHOLIPASE-A2 WITHMANOALIDE

A molecular model of the interaction between manoalide (MLD) and bee v enom phospholipase A2 (bv-PLA2) has been derived making use of a combi nation of computational methods. MLD was built in its open form and si mulated by using molecular dynamics techniques. It is shown that the p olar part of the molecule, which is thought to be the reactive region, is endowed with considerable conformational flexibility whereas the a polar region is rather rigid. The proposed active conformation of MLD and the main putative binding site for MLD on this enzyme were identif ied by matching potential energy GRID maps for both ligand and recepto r with the chemical structure of the respective counterpart. The bindi ng site is found in the C-terminal region of bv-PLA2, forming part of the proposed interfacial surface for binding to aggregated substrates, and comprises two distinct regions: (i) a hydrophobic cavity delimite d by the C-terminal beta-sheet and the antiparallel beta-sheet, which interacts with the apolar zone of MLD, and (ii) a cationic site made u p of residues Arg-58 and Lys-94, which interacts with the polar zone. Molecular dynamics and molecular orbital calculations indicate that th e most likely initial reaction between MLD and bv-PLA2 is formation of a Schiff base between Lys-94 and the aldehyde generated upon opening of MLD's gamma-lactone ring, supporting recent model reaction studies. The inhibition seems to be a consequence of the occupation by MLD of a site overlapping a phosphocholine binding site in bv-PLA2 presumably involved in the interface desolvation process. The present model repr esents a starting point for further structural studies on the mechanis m of phospholipases A2 inactivation by MLD and MLD-like compounds.