Abstract
TAT protein is an essential regulatory protein of the human immunodeficiency virus type 1 (HIV-1). Inhibition of TAT activity blocks the virus cycle, and a drug that blocks TAT is one of the possibilities to cure AIDS. Circular dichroism (CD) was measured for TAT peptides covering the TAT sequence with overlaps. The CD spectrum of each peptide was measured in different solvents to evaluate the ability of each TAT region to form different secondary structures. The most variation or conformational heterogeneity is observed with the two regions adjacent to the TAT basic region. CD data show that the basic region can adopt an extended structure in a full TAT protein, which is not the case for the isolated peptide. TAT sequences from the different HIV-1 isolates were analyzed, and the results showed that the sequences could be gathered into six groups. Molecular modeling was done on the various isolates based on a TAT structure from two-dimensional NMR. After minimization and dynamic steps, the modeled three-dimensional structures were compared. The results showed structural variations of the TAT protein as a function of the HIV-1 isolates. These structural variations were mainly in the two regions adjacent to the basic region, confirming the conformational heterogeneity indicated by the CD measurements. Furthermore, Chou-Fasman analysis shows significant changes in propensities for each secondary structure only for regions III and V. This conformational heterogeneity should be essential for TAT activity and points out that regions III and V are a poor potential target to design a TAT ligand. We propose a target involving TAT structurally conserved regions, accessible whatever the size of the TAT C terminus.
Highlights
Circular dichroism (CD) was measured for TAT peptides covering the TAT sequence with overlaps
CD data show that the basic region can adopt an extended structure in a full TAT protein, which is not the case for the isolated peptide
TAT is able to repress the transcription of the major histocompatibility complex class I gene, and a decrease in class I molecules provides for the virus a mechanism to evade the host immune response [15]
Summary
Circular dichroism (CD) was measured for TAT peptides covering the TAT sequence with overlaps. The results showed structural variations of the main containing several prolines, unable to form an ␣-helix as TAT protein as a function of the HIV-1 isolates. These previously proposed [21], and could be a motif that prevents structural variations were mainly in the two regions adjacent to the basic region, confirming the conformational heterogeneity indicated by the CD measurements. Upon binding on TAR, region V is able to form an helicoidal structure with a glutamine-rich surface and could be involved in a specific interaction with three highly conserved nucleotides located on the TAR loop [26].
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