Nucleoside–amino acid conjugates: an alternative route to the design of ribonuclease A inhibitors

Abstract

Nucleoside–amino acid conjugates have been employed to inhibit the ribonucleolytic activity of ribonuclease A (RNase A) and affect the protonation/deprotonation equilibrium of its active site histidine residues. Agarose gel and precipitation assays indicate inhibition of RNase A activity by these molecules with a possible role of the polar side chains of the amino acids in RNase A inhibition. Kinetic experiments demonstrated that the mode of inhibition is competitive in nature with inhibition constants (K_i) in the micromolar range. The nucleoside–serine conjugate occupies the active site of RNase A and preferential perturbs the pK_a value of His-119 by its 'free amino group' as found from ¹H NMR studies. Docking studies revealed that the free amino groups of the most active compounds are within hydrogen bonding distance of His-119 in inhibitor–RNase A complexes.