title: Kinetic studies of HIV-1 and HIV-2 envelope glycoprotein-mediated fusion.
abstract: BACKGROUND
  HIV envelope glycoprotein (Env)-mediated fusion is driven by the concerted coalescence of the HIV gp41 N-helical and C-helical regions, which results in the formation of 6 helix bundles. Kinetics of HIV Env-mediated fusion is an important determinant of sensitivity to entry inhibitors and antibodies. However, the parameters that govern the HIV Env fusion cascade have yet to be fully elucidated. We address this issue by comparing the kinetics HIV-1IIIB Env with those mediated by HIV-2 from two strains with different affinities for CD4 and CXCR4.
  
  
  RESULTS
  HIV-1 and HIV-2 Env-mediated cell fusion occurred with half times of about 60 and 30 min, respectively. Binding experiments of soluble HIV gp120 proteins to CD4 and co-receptor did not correlate with the differences in kinetics of fusion mediated by the three different HIV Envs. However, escape from inhibition by reagents that block gp120-CD4 binding, CD4-induced CXCR4 binding and 6-helix bundle formation, respectively, indicated large difference between HIV-1 and HIV-2 envelope glycoproteins in their CD4-induced rates of engagement with CXCR4.
  
  
  CONCLUSIONS
  The HIV-2 Env proteins studied here exhibited a significantly reduced window of time between the engagement of gp120 with CD4 and exposure of the CXCR4 binding site on gp120 as compared with HIV-1IIIB Env. The efficiency with which HIV-2 Env undergoes this CD4-induced conformational change is the major cause of the relatively rapid rate of HIV-2 Env mediated-fusion.
authors.affiliation: Center for Cancer Research Nanobiology Program, National Cancer Institute at Frederick, National Institutes of Health, Frederick, MD, USA. sgallo@aibs.org
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Gallo
authors.forename: Jacqueline D
authors.initials: JD
authors.lastname: Reeves
authors.forename: Himanshu
authors.initials: H
authors.lastname: Garg
authors.forename: Brian
authors.initials: B
authors.lastname: Foley
authors.forename: Robert W
authors.initials: RW
authors.lastname: Doms
authors.forename: Robert
authors.initials: R
authors.lastname: Blumenthal
mesh_terms: D015704:CD4 Antigens / Q000378:metabolism; D002460:Cell Line; D015699:HIV Envelope Protein gp120 / Q000378:metabolism*; D023581:HIV Fusion Inhibitors / Q000494:pharmacology; D015497:HIV-1 / Q000378:metabolism / Q000472:pathogenicity*; D015498:HIV-2 / Q000378:metabolism / Q000472:pathogenicity*; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008561:Membrane Fusion; D019718:Receptors, CXCR4 / Q000378:metabolism
chemical_list: D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D023581:HIV Fusion Inhibitors; D019718:Receptors, CXCR4