Homonuclear 1H NMR and circular dichroism study of the HIV-1 Tat Eli variant

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°C showed that Tat Eli is not a random coil at 20°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.We show that active Tat variants share a similar folding pattern whatever their size, but mutations induce local structural changes.The human immunodeficiency virus type 1 (HIV-1) trans-activator protein Tat is essential for the activation and expression of HIV genes [1]. Tat interacts with a RNA hairpin-loop structure called the trans-activation-responsive region (TAR) located at the 5' end of all nascent viral transcripts and interacts with an RNase suppressing the processing of small RNAs [2,3]. However, Tat differs from other HIV-1 regulatory proteins due to its early secretion from HIV-1-infected CD4+ T cells [4]. Extracellular Tat can traverse cellular membranes and induce apoptosis preventing the immune system from eliminating HIV-1-infected cells [5]. Tat is encoded by two exons. The first exon encodes amino acids 1–72 and the second exon encodes amino acids 73–86/101 that contribute to viral infectivity and other functions such as the induction of CD4+ T cell apoptosis [6].A vaccine targeting Tat could help restore cellular immunity in HIV-1-infected patients [7]. A recent study using autologous dendritic cells, loaded with exogenous simian immunodeficiency virus peptides that spanned the overlapping reading fra