1 HIV-1 Protease Dimer Interface Mutations that Compensate for Viral Reverse Transcriptase Instability in Infectious Virions

Mature enzymes encoded within the human immunodeficiency virus type 1 (HIV-1) genome [protease (PR), reverse transcriptase (RT) and integrase (IN)] derive from proteolytic processing of a large polyprotein (Gag-Pol). Gag-Pol processing is catalyzed by the viral PR, which is active as a homodimer. The HIV-1 RT functions as a heterodimer (p66/p51) composed of subunits of 560 and 440 amino acids, respectively. Both subunits have identical amino acid sequence, but p51 lacks 120 residues which are removed by the HIV-1 PR during viral maturation. While p66 is the catalytic subunit, p51 has a primarily structural role. Amino acid substitutions affecting the stability of p66/p51 (i.e. F130W) have a deleterious effect on viral fitness. Previously we showed that the effects of F130W are mediated by p51 and can be compensated by mutation T58S. While studying the dynamics of emergence of the compensatory mutation, we observed that mutations in viral PR-coding region were selected in HIV clones containing the RT substitution F130W, before the imposition of T58S/F130W mutations. The identified PR mutations (G94S and T96S) improved the replication capacity of the F130W mutant virus. By using a trans-complementation assay, we demonstrate that the loss of p66/p51 heterodimer stability caused by Trp-130 can b