*European Molecular Biology Laboratory, Heidelberg'FRG
**R D Departament, Laboratories Menarini S.A.Badalona, Spain
a Departamento di Fisiologia y Farmacologia, Universidad
de Alcala de Henares, Madrid, Spain
GRID is a computational procedure for detecting energetically favorable
binding sites on molecules of known structure.' LUDI is a recently introduced
automatic method for de novo ligand design. A combination of both
methodologies has been used here to suggest modifications that could be
introduced into the structure of a known phospholipase A2 (PLA2)
inhibitor in order to enhance its binding affinity for this enzyme.
PLA2 is a lipolytic enzyme that splits the 2-acyl bond in
1,2-diacylphosphatides. Release of fatty acids provides the substrate required
for the synthesis of eicosanoids, involved in pathological processes such
as inflammation. Thus, modulation of PLA2 activity is a pharmacological
goal of great interest. The three-dimensional structure of the human synovial
fluid PLA2 (HSF-PLA2) is known both in its native
form and in a complex with the transition state analogue L-1-O-octyl-2-heptylphosphonyl-sn-glycero-3-phosphoethanolomine.
Novel putative ligand-binding sites on HSF-PLA2 were identified
by use of water and aromatic atom probes, as implemented in the GRID suite
of programs. Strong hydrophobic and aromatic interactions were observed
within a cage region on the surface of the enzyme delimited by residues
VAL46, THR130, PRO131, GLY33, and the disulfide bridge linking CYS50 and
CYS133. LUDI was also used to explore the same enzyme substructure. An
interesting suggestion from this program was that this hydrophobic region
could be filled with an aromatic ring template.
In the known enzyme-inhibitor complex, the amino group of the inhibitor
is located close to the above mentioned region. Therefore, the rationale
for structural modification of this inhibitor was that exploitation of
this additional interaction site could lead to enhanced affinity for the
enzyme. 2-Decylsulfonylamino-1-octyl-phosphoglycol (LM- 1230) and its O-benzyl
ether derivate (LM-1228) were synthesised and tested. Their inhibition
of HSF-PLA2 activity yielded Xi(50) values of 0.026 and 0.0036,
respectively. Therefore, these bencylated derivates are indeed endowed
with the predicted enhancement in affinity, and present a good inhibitory
activity.
J. Mol. Graph. (1994) 12, 72.