title: Homonuclear 1H NMR and circular dichroism study of the HIV-1 Tat Eli variant.
abstract: BACKGROUND
  The HIV-1 Tat protein is a promising target to develop AIDS therapies, particularly vaccines, due to its extracellular role that protects HIV-1-infected cells from the immune system. Tat exists in two different lengths, 86 or 87 residues and 99 or 101 residues, with the long form being predominant in clinical isolates. We report here a structural study of the 99 residue Tat Eli variant using 2D liquid-state NMR, molecular modeling and circular dichroism.
  
  
  RESULTS
  Tat Eli was obtained from solid-phase peptide synthesis and the purified protein was proven biologically active in a trans-activation assay. Circular dichroism spectra at different temperatures up to 70 degrees C showed that Tat Eli is not a random coil at 20 degrees C. Homonuclear 1H NMR spectra allowed us to identify 1639 NMR distance constraints out of which 264 were interresidual. Molecular modeling satisfying at least 1474 NMR constraints revealed the same folding for different model structures. The Tat Eli model has a core region composed of a part of the N-terminus including the highly conserved Trp 11. The extra residues in the Tat Eli C-terminus protrude from a groove between the basic region and the cysteine-rich region and are well exposed to the solvent.
  
  
  CONCLUSIONS
  We show that active Tat variants share a similar folding pattern whatever their size, but mutations induce local structural changes.
authors.affiliation: Faculté de Pharmacie, Unité Mixte de Recherche Université de la Méditerranée/INSERM U911, Université de la Méditerranée, Marseille, France. jennifer.watkins@pharmacie.univ-mrs.fr
authors.forename: Jennifer D
authors.initials: JD
authors.lastname: Watkins
authors.forename: Grant R
authors.initials: GR
authors.lastname: Campbell
authors.forename: Hubert
authors.initials: H
authors.lastname: Halimi
authors.forename: Erwann P
authors.initials: EP
authors.lastname: Loret
mesh_terms: D002942:Circular Dichroism; D015497:HIV-1 / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000737:chemistry*
chemical_list: D054322:tat Gene Products, Human Immunodeficiency Virus