title: Resistance to N-peptide fusion inhibitors correlates with thermodynamic stability of the gp41 six-helix bundle but not HIV entry kinetics.
abstract: BACKGROUND
  The HIV-1 envelope glycoprotein (Env) undergoes conformational changes that mediate fusion between virus and host cell membranes. These changes involve transient exposure of two heptad-repeat domains (HR1 and HR2) in the gp41 subunit and their subsequent self-assembly into a six-helix bundle (6HB) that drives fusion. Env residues and features that influence conformational changes and the rate of virus entry, however, are poorly understood. Peptides corresponding to HR1 and HR2 (N and C peptides, respectively) interrupt formation of the 6HB by binding to the heptad repeats of a fusion-intermediate conformation of Env, making the peptides valuable probes for studying Env conformational changes.
  
  
  RESULTS
  Using a panel of Envs that are resistant to N-peptide fusion inhibitors, we investigated relationships between virus entry kinetics, 6HB stability, and resistance to peptide fusion inhibitors to elucidate how HR1 and HR2 mutations affect Env conformational changes and virus entry. We found that gp41 resistance mutations increased 6HB stability without increasing entry kinetics. Similarly, we show that increased 6HB thermodynamic stability does not correlate with increased entry kinetics. Thus, N-peptide fusion inhibitors do not necessarily select for Envs with faster entry kinetics, nor does faster entry kinetics predict decreased potency of peptide fusion inhibitors.
  
  
  CONCLUSIONS
  These findings provide new insights into the relationship between 6HB stability and viral entry kinetics and mechanisms of resistance to inhibitors targeting fusion-intermediate conformations of Env. These studies further highlight how residues in HR1 and HR2 can influence virus entry by altering stability of the 6HB and possibly other conformations of Env that affect rate-limiting steps in HIV entry.
authors.affiliation: Center for Biologics Evaluation and Research, US Food and Drug Administration, Silver Spring, MD, 20993, USA. christopher.defeo@fda.hhs.gov.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: De Feo
authors.affiliation: Center for Biologics Evaluation and Research, US Food and Drug Administration, Silver Spring, MD, 20993, USA. wei.wang@fda.hhs.gov.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Center for Biologics Evaluation and Research, US Food and Drug Administration, Silver Spring, MD, 20993, USA. menglunhsieh@gmail.com.|Present address: Michigan State University, Department of Biochemistry and Molecular Biology, Lansing, MI, 48824, USA. menglunhsieh@gmail.com.
authors.forename: Meng-Lun
authors.initials: ML
authors.lastname: Hsieh
authors.affiliation: Center for Biologics Evaluation and Research, US Food and Drug Administration, Silver Spring, MD, 20993, USA. mznorthbethesda@gmail.com.|Present address: Department of Microbiology, Harbin Medical University, Harbin, Heilongjiang, China. mznorthbethesda@gmail.com.
authors.forename: Min
authors.initials: M
authors.lastname: Zhuang
authors.affiliation: Center for Biologics Evaluation and Research, US Food and Drug Administration, Silver Spring, MD, 20993, USA. russell.vassell@fda.hhs.gov.
authors.forename: Russell
authors.initials: R
authors.lastname: Vassell
authors.affiliation: Center for Biologics Evaluation and Research, US Food and Drug Administration, Silver Spring, MD, 20993, USA. carol.weiss@fda.hhs.gov.
authors.forename: Carol D
authors.initials: CD
authors.lastname: Weiss
mesh_terms: D002460:Cell Line; D024882:Drug Resistance, Viral; D015700:HIV Envelope Protein gp41 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D023581:HIV Fusion Inhibitors / Q000378:metabolism*; D015497:HIV-1 / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D006801:Humans; D007700:Kinetics; D046912:Multiprotein Complexes / Q000737:chemistry*; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D055503:Protein Multimerization; D055550:Protein Stability; D013816:Thermodynamics; D053586:Virus Internalization / Q000187:drug effects*
chemical_list: D015700:HIV Envelope Protein gp41; D023581:HIV Fusion Inhibitors; D046912:Multiprotein Complexes; D050505:Mutant Proteins; C514787:gp41 protein, Human immunodeficiency virus 1