title: The inhibition of assembly of HIV-1 virus-like particles by 3-O-(3',3'-dimethylsuccinyl) betulinic acid (DSB) is counteracted by Vif and requires its Zinc-binding domain.
abstract: BACKGROUND
  DSB, the 3-O-(3',3'dimethylsuccinyl) derivative of betulinic acid, blocks the last step of protease-mediated processing of HIV-1 Gag precursor (Pr55Gag), which leads to immature, noninfectious virions. When administered to Pr55Gag-expressing insect cells (Sf9), DSB inhibits the assembly and budding of membrane-enveloped virus-like particles (VLP). In order to explore the possibility that viral factors could modulate the susceptibility to DSB of the VLP assembly process, several viral proteins were coexpressed individually with Pr55Gag in DSB-treated cells, and VLP yields assayed in the extracellular medium.
  
  
  RESULTS
  Wild-type Vif (Vifwt) restored the VLP production in DSB-treated cells to levels observed in control, untreated cells. DSB-counteracting effect was also observed with Vif mutants defective in encapsidation into VLP, suggesting that packaging and anti-DSB effect were separate functions in Vif. The anti-DSB effect was abolished for VifC133S and VifS116V, two mutants which lacked the zinc binding domain (ZBD) formed by the four H(108)C(114)C(133)H(139) coordinates with a Zn atom. Electron microscopic analysis of cells coexpressing Pr55Gag and Vifwt showed that a large proportion of VLP budded into cytoplasmic vesicles and were released from Sf9 cells by exocytosis. However, in the presence of mutant VifC133S or VifS116V, most of the VLP assembled and budded at the plasma membrane, as in control cells expressing Pr55Gag alone.
  
  
  CONCLUSIONS
  The function of HIV-1 Vif protein which negated the DSB inhibition of VLP assembly was independent of its packaging capability, but depended on the integrity of ZBD. In the presence of Vifwt, but not with ZBD mutants VifC133S and VifS116V, VLP were redirected to a vesicular compartment and egressed via the exocytic pathway.
authors.affiliation: Université de Lyon I-Claude Bernard, Faculté de Médecine Laënnec, Laboratoire de Virologie & Pathologie Humaine, CNRS FRE-3011, 69372 Lyon Cedex 08, France. sandrinedafonseca@hotmail.com
authors.forename: Sandrina
authors.initials: S
authors.lastname: Dafonseca
authors.forename: Pascale
authors.initials: P
authors.lastname: Coric
authors.forename: Bernard
authors.initials: B
authors.lastname: Gay
authors.forename: Saw See
authors.initials: SS
authors.lastname: Hong
authors.forename: Serge
authors.initials: S
authors.lastname: Bouaziz
authors.forename: Pierre
authors.initials: P
authors.lastname: Boulanger
mesh_terms: D000818:Animals; D019380:Anti-HIV Agents / Q000494:pharmacology*; D002460:Cell Line; D015497:HIV-1 / Q000187:drug effects* / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D013386:Succinates / Q000494:pharmacology*; D014315:Triterpenes / Q000494:pharmacology*; D014771:Virion / Q000187:drug effects / Q000502:physiology; D019065:Virus Assembly / Q000187:drug effects*; D015032:Zinc / Q000378:metabolism*; D054320:vif Gene Products, Human Immunodeficiency Virus / Q000235:genetics / Q000378:metabolism*; D053978:Pentacyclic Triterpenes
chemical_list: D019380:Anti-HIV Agents; D013386:Succinates; D014315:Triterpenes; D015032:Zinc; D054320:vif Gene Products, Human Immunodeficiency Virus; C514847:vif protein, Human immunodeficiency virus 1; C479935:bevirimat; D053978:Pentacyclic Triterpenes