Structural basis of the allosteric inhibitor interaction on the HIV-1 reverse transcriptase RNase H domain

HIV-1 reverse transcriptase (RT) has been an attractive target for the development of antiretroviral agents. Although this enzyme is bi-functional, having both DNA polymerase and ribonuclease H (RNH) activities, there is no clinically approved inhibitor of the RNH activity. Here, we characterize the structural basis and molecular interaction of an allosteric site inhibitor, BHMP07, with the wild-type (WT) RNH fragment. Solution NMR experiments for inhibitor titration on WT RNH showed relatively wide chemical shift perturbations, suggesting a long-range conformational effect on the inhibitor interaction. Comparisons of the inhibitor-induced NMR chemical shift changes of RNH with those of RNH dimer, in the presence and absence of Mg(2+) , were performed to determine and verify the interaction site. The NMR results, with assistance of molecular docking, indicate that BHMP07 preferentially binds to a site that is located between the RNH active site and the region encompassing helices B and D (the 'substrate-handle region'). The interaction site is consistent with the previous proposed site, identified using a chimeric RNH (p15-EC) [Gong et al. (2011) Chem Biol Drug Des 77, 39-47], but with slight differences that reflect the characteristics of the amino acid sequences in p15-EC compared to the WT RNH.