AMINO-ACID SUBSTITUTIONS IN HIV-1 REVERSE-TRANSCRIPTASE WITH CORRESPONDING RESIDUES FROM HIV-2 - EFFECT ON KINETIC CONSTANTS AND INHIBITIONBY NONNUCLEOSIDE ANALOGS

Nevirapine is a highly potent and specific inhibitor of human immunode ficiency virus type 1 (HIV-1) polymerase, but is inactive against HIV- 2 and other polymerases. Previous studies demonstrated that residues 1 76-190 of HIV-1 reverse transcriptase (RT) can confer nevirapine sensi tivity to HIV-2 RT. To better characterize the role of this sequence i n HIV-1 RT, we have progressively substituted residues 176-190 of HIV- 2 RT for those of HIV-1 RT and monitored the impact on the kinetic pro perties; inhibitory activity of nevirapine yl-6H-dipyrido2,3-b:2',3'- e!1,4!diazepin-6-one), E-BPU (5-ethyl-1-benzyloxymethyl-6-(phenylthio )-uracil), and TIBO-R82150 o-5-methyl-6-(3-methyl-2-butenyl)imidazo4, 5,1-jk! 1,4!benzodiazepin-2(1H)-thione); and inhibitor-induced fluore scence changes of the mutant enzymes. The study revealed that in addit ion to Tyr-181 and Tyr- 188, a new amino acid residue (Gly-190) plays an important role in determining susceptibility to nevirapine and E-BP U, but not to TIBO-R82150. These data argue that these non-nucleoside inhibitors fit differently, even though they share a common binding po cket. Nevirapine was seen to exert inhibitory activity by altering the interaction of the enzyme with the template-primer. Kinetic parameter s were modulated by the template (DNA versus RNA) as well as by some o f the mutations.