title: Identification and characterization of a subpocket on the N-trimer of HIV-1 Gp41: implication for viral entry and drug target.
abstract: OBJECTIVE
  Crystallographic studies of HIV-1 gp41 demonstrate a stable six-helix bundle (6-HB) folded by trimeric N and C-terminal heptad repeats (NHR and CHR), and a deep hydrophobic pocket (pocket-1) on the NHR helices (N-trimer); however, previous crystal structures of 6-HB core were determined by peptide fragments missing the downstream sequence of pocket-1; thus, the structural features of this site could not be observed.
  
  
  METHODS
  We recently determined several 6-HB structures containing the pocket-1 and its downstream site. Here, we focused to investigate the structural features of N-trimer previously uncharacterized.
  
  
  METHODS
  Biophysical, biochemical and functional approaches were combined to characterize the downstream residues of pocket-1.
  
  
  RESULTS
  A subpocket (designated pocket-2) was visualized on the C-terminal portion of N-trimer, which is formed by a cluster of seven residues, including Leu587, Lys588 and Glu584 on one NHR helix and Tyr586, Val583, Ala582 and Arg579 of another NHR helix. Mutagenesis studies demonstrated that the pocket-2 residues play essential roles for HIV-1 Env-mediated cell entry and critically determine the antiviral activity of NHR-derived peptide fusion inhibitor T21. Further, the pocket-2 mutations dramatically impaired the thermostability and conformation of 6-HB structure and reduced the binding affinity of CHR-derived inhibitor HP23 that specifically targets the deep pocket-1.
  
  
  CONCLUSIONS
  These data have provided important information for the structure-function relationship of HIV-1 gp41 and for the development of antiviral entry inhibitors.
authors.affiliation: MOH Key Laboratory of Systems Biology of Pathogens and AIDS Research Center, Institute of Pathogen Biology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China. *Both Sheng Cui and Yuxian He contributed equally to this work.
authors.forename: Zonglin
authors.initials: Z
authors.lastname: Qiu
authors.forename: Huihui
authors.initials: H
authors.lastname: Chong
authors.forename: Xue
authors.initials: X
authors.lastname: Yao
authors.forename: Yang
authors.initials: Y
authors.lastname: Su
authors.forename: Sheng
authors.initials: S
authors.lastname: Cui
authors.forename: Yuxian
authors.initials: Y
authors.lastname: He
mesh_terms: D018360:Crystallography, X-Ray; D004252:DNA Mutational Analysis; D015700:HIV Envelope Protein gp41 / Q000737:chemistry* / Q000378:metabolism*; D023581:HIV Fusion Inhibitors / Q000378:metabolism* / Q000494:pharmacology*; D015497:HIV-1 / Q000502:physiology*; D006801:Humans; D008958:Models, Molecular; D011487:Protein Conformation; D053586:Virus Internalization / Q000187:drug effects*
chemical_list: D015700:HIV Envelope Protein gp41; D023581:HIV Fusion Inhibitors; C514787:gp41 protein, Human immunodeficiency virus 1