Human Immunodeficiency Virus Type 1 Reverse Transcriptase Dimer Destabilization by 1-{Spiro[4‘ ‘-amino-2‘ ‘,2‘ ‘-dioxo-1‘ ‘,2‘ ‘-oxathiole-5‘ ‘,3‘- [2‘,5‘-bis-O-(tert-butyldimethylsilyl)-β-d-ribofuranosyl]]}-3-ethylthymine^†

The nonnucleoside inhibitor binding pocket is a well-defined region in the p66 palm domain of the human immunodeficiency virus type-1 reverse transcriptase (HIV-1 RT). This binding pocket opens toward the interface of the p66/p51 heterodimer and we have investigated whether ligand binding at or near this site induces structural changes that have an impact on the dimeric structure of HIV-1 RT. 1-[2‘,5‘-bis-O-(tert-butyldimethylsilyl]-3‘-spiro-5‘ ‘-(4‘ ‘-amino-1‘ ‘,2‘ ‘-oxathiole-2‘ ‘,2‘ ‘-dioxide)-3-ethylthymine (TSAOe³T) was found to destabilize the subunit interactions of both the p66/p51 heterodimer and p66/p66 homodimer enzymes. The Gibbs free energy of dimer dissociation (ΔG_D^H₂O) is decreased with increasing concentrations of TSAOe³T, resulting in a loss in dimer stability of 4.0 and 3.2 kcal/mol for the p66/p51 and p66/p66 HIV-1 RT enzymes, respectively. This loss of energy is not sufficient to induce the dissociation of the subunits in the absence of denaturant. This destabilizing effect seems to be unique for TSAOe³T, since neither the tight-binding inhibitor UC781 nor nevirapine showed any effects on the stability of HIV-1 RT dimers. TSAOe³T was unable to destabilize the subunit interactions of the E138K mutant enzyme, which exhibits significant resistance to TSAOe³T inhibition. Molecular modeling of TSAOm³T into the nonnucleoside inhibitor binding pocket of wild-type RT suggests that it makes significant interactions with the p51 subunit of the enzyme, a feature that has not been observed with other types of nonnucleoside inhibitors. The observed destabilization of the dimeric HIV-1 RT may result from structural/conformational perturbations at the reverse transcriptase subunit interface.