title: Uneven genetic robustness of HIV-1 integrase.
abstract: Genetic robustness (tolerance of mutation) may be a naturally selected property in some viruses, because it should enhance adaptability. Robustness should be especially beneficial to viruses like HIV-1 that exhibit high mutation rates and exist in immunologically hostile environments. Surprisingly, however, the HIV-1 capsid protein (CA) exhibits extreme fragility. To determine whether fragility is a general property of HIV-1 proteins, we created a large library of random, single-amino-acid mutants in HIV-1 integrase (IN), covering >40% of amino acid positions. Despite similar degrees of sequence variation in naturally occurring IN and CA sequences, we found that HIV-1 IN was significantly more robust than CA, with random nonsilent IN mutations only half as likely to cause lethal defects. Interestingly, IN and CA were similar in that a subset of mutations with high in vitro fitness were rare in natural populations. IN mutations of this type were more likely to occur in the buried interior of the modeled HIV-1 intasome, suggesting that even very subtle fitness effects suppress variation in natural HIV-1 populations. Lethal mutations, in particular those that perturbed particle production, proteolytic processing, and particle-associated IN levels, were strikingly localized at specific IN subunit interfaces. This observation strongly suggests that binding interactions between particular IN subunits regulate proteolysis during HIV-1 virion morphogenesis. Overall, use of the IN mutant library in conjunction with structural models demonstrates the overall robustness of IN and highlights particular regions of vulnerability that may be targeted in therapeutic interventions.
  
  
  OBJECTIVE
  The HIV-1 integrase (IN) protein is responsible for the integration of the viral genome into the host cell chromosome. To measure the capacity of IN to maintain function in the face of mutation, and to probe structure/function relationships, we created a library of random single-amino-acid IN mutations that could mimic the types of mutations that naturally occur during HIV-1 infection. Previously, we measured the robustness of HIV-1 capsid in this manner and determined that it is extremely intolerant of mutation. In contrast to CA, HIV-1 IN proved relatively robust, with far fewer mutations causing lethal defects. However, when we subsequently mapped the lethal mutations onto a model of the structure of the multisubunit IN-viral DNA complex, we found the lethal mutations that caused virus morphogenesis defects tended to be highly localized at subunit interfaces. This discovery of vulnerable regions of HIV-1 IN could inform development of novel therapeutics.
authors.affiliation: Aaron Diamond AIDS Research Center, The Rockefeller University, New York, New York, USA Laboratory of Retrovirology, The Rockefeller University, New York, New York, USA.
authors.forename: Suzannah J
authors.initials: SJ
authors.lastname: Rihn
authors.affiliation: MRC University of Glasgow Centre for Virus Research, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, Glasgow, United Kingdom.
authors.forename: Joseph
authors.initials: J
authors.lastname: Hughes
authors.affiliation: MRC University of Glasgow Centre for Virus Research, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, Glasgow, United Kingdom.
authors.forename: Sam J
authors.initials: SJ
authors.lastname: Wilson
authors.affiliation: Aaron Diamond AIDS Research Center, The Rockefeller University, New York, New York, USA Laboratory of Retrovirology, The Rockefeller University, New York, New York, USA Howard Hughes Medical Institute, Aaron Diamond AIDS Research Center, New York, New York, USA pbienias@adarc.org.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Bieniasz
mesh_terms: D019943:Amino Acid Substitution; D016655:HIV Core Protein p24 / Q000235:genetics / Q000378:metabolism; D019427:HIV Integrase / Q000235:genetics* / Q000378:metabolism*; D015497:HIV-1 / Q000201:enzymology* / Q000502:physiology*; D050296:Microbial Viability; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense
chemical_list: D016655:HIV Core Protein p24; D050505:Mutant Proteins; D019427:HIV Integrase; C514801:p31 integrase protein, Human immunodeficiency virus 1