Mechanisms of hepatitis C virus NS3 proteinase inhibitors

The NS3 serine proteinase is regarded as one of the preferred targets for t he development of therapeutic agents against hepatitis C virus (HCV), Possi ble mechanisms of NS3 inhibitors include: ii) interference with the activat ion of the enzyme by its NS4A cofactor: iii) binding to the structural zinc site; and (iii) binding to the active site. These mechanisms have been exp lored in detail by structural analysis of the enzyme. (ii) The NS4A cofactor binds to the amino-terminal beta-barrel domain of th e NS3 proteinase bringing about several conformational changes that result in enzyme activation, The interaction betweeen NS3 and NS4A involves a very large surface area and therefore it is not a likely target for the develop ment of inhibitors. (ii) The NS3 proteinase contains a structural zinc bind ing site. Spectroscopic studies have shown that changes in the conformation of this metal-binding site correlate with changes in the specific activity of the enzyme, and the NS3 proteinase is inhibited by compounds capable of extracting zinc from its native coordination sphere. (iii) Based on the ob servation that the NS3 proteinase undergoes inhibition by its cleavage prod ucts, potent, active site-directed inhibitors have been generated. Kinetic studies, site-directed mutagenesis, and molecular modelling have been used to characterize the interactions between the NS3 proteinase and its product inhibitors.