Positional preferences in flavonoids for inhibition of ribonuclease A: Where "OH" where?

Flavonoids are a class of polyphenols that possess diverse properties. The structure-activity relationship of certain flavonoids and resveratrol with ribonuclease A (RNase A) has been investigated. The selected flavonoids have a similar skeleton and the positional preferences of the phenolic moieties toward inhibition of the catalytic activity of RNase A have been studied. The results obtained for RNase A inhibition by flavonoids suggest that the planarity of the molecules is necessary for effective inhibitory potency. Agarose gel electrophoresis and precipitation assay experiments along with kinetic studies reveal K_i values for the various flavonoids in the micromolar range. Minor secondary structural changes of RNase A were observed after interaction with the flavonoids. An insight into the specific amino acid involvement in the binding of the substrate using docking studies is also presented. The dipole moment of the flavonoids that depends on the orientation of the hydroxyl groups in the molecule bears direct correlation with the inhibitory potency against RNase A. The direct association of this molecular property with enzyme inhibition can be exploited for the design and development of inhibitors of proteins.