The N137 and P140 amino acids in the p51 and the P95 amino acid in the p66 subunit of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase are instrumental to maintain catalytic activity and to design new classes of anti-HIV-1 drugs.

Amino acids N137 and P140 in the p51 subunit of HIV-1 reverse transcriptase (RT) are part of the beta7-beta8-loop that contributes to the formation of the base of the non-nucleoside RT inhibitor (NNRTI)-binding pocket and makes up a substantial part of the dimerization interface. Amino acid P95 in p66 also markedly contributes to the dimerization binding energy. Nine RT mutants at amino acid 137 were constructed bearing the mutations Y, K, T, D, A, Q, S, H or E. The prolines at amino acid positions 95 and 140 were replaced by alanine in separate enzymes. We found that all mutant RT enzymes showed a dramatically decreased RNA-dependent DNA polymerase activity. None of the mutant RT enzymes showed marked resistance against any of the clinically used NNRTIs but they surprisingly lost significant sensitivity for NRTIs such as ddGTP. The denaturation analyses of the mutant RTs by urea are suggestive for a relevant role of N137 in the stability of the RT heterodimer and support the view that the beta7-beta8 loop in p51 is a hot spot for RT dimerization and instrumental for efficient polymerase catalytic activity. Consequently, N137 and P140 in p51 and P95 in p66 should be attractive targets in the design of new structural classes of RT inhibitors aimed at compromising the optimal interaction of the beta7-beta8 loop in p51 at the p66/p51 dimerization interface.