The thumb domain of the P51-subunit is essential for activation of HIV reverse transcriptase

The biologically relevant and active form of human immunodeficiency virus r everse transcriptase is a heterodimer produced in a two-step dimerization p rocess. Dimerization involves first the rapid association of the two subuni ts, followed by a slow conformational change yielding a fully active form. In the present study, we demonstrate that the interaction between the thumb domain of p51 and the RNase-H domain of p66 plays a major role in an essen tial conformational change required for proper folding of the primer/templa te and the tRNA-binding site, for maturation and for activation of heterodi meric reverse transcriptase, A synthetic peptide derived from the sequence within the thumb domain of p51, which forms the interface with the RNase-H domains of p66, binds heterodimeric reverse transcriptase with an apparent dissociation constant in the nanomolar range and selectively inhibits activ ation of heterodimeric reverse transcriptase with an inhibition constant of 1.2 mu M. A detailed study of the mechanism of inhibition reveals that thi s peptide does not require dissociation of heterodimeric RT for efficient i nhibition and does not affect subunit association, but interferes with the conformational change required for activation of heterodimeric reverse tran scriptase, resulting in a decrease in the affinity of reverse transcriptase for the tRNA and an increase in the stability of the primer/template/rever se transcriptase complex. We have previously proposed that the dimeric natu re of reverse transcriptase represents an interesting target for the design of antiviral agents. On the basis of this work, we propose that the confor mational changes involved in the activation of reverse transcriptase simila rly represent an important target for the design of novel antiviral compoun ds,