Full peptide synthesis, purification, and characterization of six Tat variants - Differences observed between HIV-1 isolates from Africa and other continents

AIDS in Africa is characterized by the equal distribution of mortality betw een the two genders because of highly virulent human immunodeficiency virus type I (HIV-1) strains. The viral protein Tat trans-activates viral gene e xpression and is essential for HIV-1 replication. We chemically synthesized six different Tat proteins, with sizes ranging from 86 to 101 residues, fr om HIV-1 isolates located in different parts of the world including highly virulent African strains. Protein purification, mass spectroscopy, and amin o acid analysis showed that the synthesis was successful in each case but w ith different yields. We show that all have the ability to bind the HIV lon g terminal repeat (LTR) RNA trans-activation response element (TAR) region, involved in Tat-mediated trans-activation, but structural heterogeneities are revealed by circular dichroism. These Tat synthetic proteins cross memb ranes but differ in their ability to trans-activate an HIV LTR-reporter gen e in stably transfected HeLa cells. Two Tat proteins from virulent African HIV-1 strains were much more active than those from Europe and the United S tates. The interferon-induced kinase (PKR), involved in cell antiviral defe nse, phosphorylates only Tat variants corresponding to less or nonvirulent HIV-1 isolates. Our results indicate that the high virulence of some Africa n HN-I strains could be related to Tat activity.