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)-beta-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 transcri ptase (HIV-I 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 st ructure of HIV-1 RT. 1-[2',5'-bis-O-(tert-butyldimethylsilyl]-3'-spiro-5 "- (4 "-amino-1 ",2 "-oxathiole-2 ",2 "-dioxide)-3-ethylthymine (TSAOe(3)T) wa s found to destabilize the subunit interactions of both the p66/p51 heterod imer and p66/p66 homodimer enzymes. The Gibbs free energy of dimer dissocia tion (Delta G(D)(H2O)) is decreased with increasing concentrations of TSAOe (3)T, resulting in a loss in dimer stability of 4.0 and 3.2 kcal/mol for th e p66/p51 and p66/p66 HIV-1 RT enzymes, respectively. This loss of energy i s not sufficient to induce the dissociation of the subunits in the absence of denaturant. This destabilizing effect seems to be unique for TSAOe(3)T, since neither the tight-binding inhibitor UC781 nor nevirapine showed any e ffects on the stability of HIV-I RT dimers. TSAOe(3)T was unable to destabi lize the subunit interactions of the E138K mutant enzyme, which exhibits si gnificant resistance to TSAOe(3)T inhibition. Molecular modeling of TSAOm(3 )T 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 inh ibitors. The observed destabilization of the dimeric HIV-1 RT may result fr om structural/conformational perturbations at the reverse transcriptase sub unit interface.