title: Interplay between single resistance-associated mutations in the HIV-1 protease and viral infectivity, protease activity, and inhibitor sensitivity.
abstract: Resistance-associated mutations in the HIV-1 protease modify viral fitness through changes in the catalytic activity and altered binding affinity for substrates and inhibitors. In this report, we examine the effects of 31 mutations at 26 amino acid positions in protease to determine their impact on infectivity and protease inhibitor sensitivity. We found that primary resistance mutations individually decrease fitness and generally increase sensitivity to protease inhibitors, indicating that reduced virion-associated protease activity reduces virion infectivity and the reduced level of per virion protease activity is then more easily titrated by a protease inhibitor. Conversely, mutations at more variable positions (compensatory mutations) confer low-level decreases in sensitivity to all protease inhibitors with little effect on infectivity. We found significant differences in the observed effect on infectivity with a pseudotype virus assay that requires the protease to cleave the cytoplasmic tail of the amphotropic murine leukemia virus (MuLV) Env protein. Additionally, we were able to mimic the fitness loss associated with resistance mutations by directly reducing the level of virion-associated protease activity. Virions containing 50% of a D25A mutant protease were 3- to 5-fold more sensitive to protease inhibitors. This level of reduction in protease activity also resulted in a 2-fold increase in sensitivity to nonnucleoside inhibitors of reverse transcriptase and a similar increase in sensitivity to zidovudine (AZT), indicating a pleiotropic effect associated with reduced protease activity. These results highlight the interplay between enzyme activity, viral fitness, and inhibitor mechanism and sensitivity in the closed system of the viral replication complex.
authors.affiliation: UNC Center for AIDS Research, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Gavin J
authors.initials: GJ
authors.lastname: Henderson
authors.forename: Sook-Kyung
authors.initials: SK
authors.lastname: Lee
authors.forename: David M
authors.initials: DM
authors.lastname: Irlbeck
authors.forename: Janera
authors.initials: J
authors.lastname: Harris
authors.forename: Melissa
authors.initials: M
authors.lastname: Kline
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Pollom
authors.forename: Neil
authors.initials: N
authors.lastname: Parkin
authors.forename: Ronald
authors.initials: R
authors.lastname: Swanstrom
mesh_terms: D000818:Animals; D002460:Cell Line; D024882:Drug Resistance, Viral / Q000187:drug effects / Q000235:genetics*; D015686:Gene Products, env / Q000235:genetics / Q000378:metabolism; D016333:HIV Protease / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D017320:HIV Protease Inhibitors / Q000494:pharmacology*; D015497:HIV-1 / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000472:pathogenicity*; D006801:Humans; D009052:Leukemia Virus, Murine / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008826:Microbial Sensitivity Tests; D009154:Mutation; D014771:Virion / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000472:pathogenicity; D014779:Virus Replication / Q000187:drug effects / Q000502:physiology
chemical_list: D015686:Gene Products, env; D017320:HIV Protease Inhibitors; D016333:HIV Protease; C514803:p16 protease, Human immunodeficiency virus 1
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