Isozymes inhibited by active site blocking: versatility of calcium indifferent hesperidin binding to phospholipase A and its significance.

sPLA is released under inflammatory conditions from neutrophils, basophils and T-cells. They cleave the cellular phospholipids leading to the release of arachidonic acid and there by provide intermediates for biosynthesis of inflammatory mediators. The focus of this study is on the interaction of hesperidin, a natural flavonoid with Group IB, IIA, and V and X isozymes of sPLA. Affinity of hesperidin towards PLA isozymes was analyzed through enzymatic studies and molecular modeling. The experiments showed that hesperidin competitively inhibited PLA with IC of 5.1 µM. Molecular modeling studies revealed the association of hesperidin with the docking scores -6.90, -9.53, -5.63 and -8.29 kcal for isozymes Group IB, IIA, V and X of PLA respectively. Their binding energy values were calculated as -20.25, -21.63, -21.66 and -33.43 kcal for the Group IB, IIA, V and X respectively. Structural model for Group V was made by homology modeling since no structural coordinates were available. Molecular dynamics studies were carried out to evaluate the structural stability of protein ligand complex. The analyses showed that hesperidin blocked the entry of the substrate to the active site of PLA and it was indifferent to the differences of the isozymes. Hence, hesperidin might serve as lead for designing highly specific anti-inflammatory drugs directed to the PLA isozyme specific to various diseases, with IC value of therapeutic significance.