Homonuclear H-1-NMR Assignment and Structural Characterization of Human Immunodeficiency Virus Type 1 Tat Mal Protein

The transacting transcriptional activator (Tat) is a viral protein essentia l for activation of the human immunodeficiency virus (HIV) genes, and it pl ays an important role in HIV induced immunodeficiency. We report the NMR st ructural characterization of the active Tat Mal variant that belongs to a h ighly virulent D-subtype HIV type-1 (HIV-1) strain (Mal) found mainly in Af rica. A full Tat Mal protein (87 residues) is synthesized. This synthetic p rotein is active in a transactivation assay with HeLa cells infected with t he HIV long terminal. repeated noncoding sequences of the HIV-1 provirus (L TR) lac Z gene. Homonuclear H-1-NMR spectra allows the sequential assignmen t of the Tat Mal spin systems. Simulating annealing generates 20 conformers with similar folding. The geometry of the mean structure is optimized with energy minimization to obtain a final structure. As the European variant ( Tat Bru) the N-terminal region of Tat Mal constitutes the core, and there i s a hydrophobic pocket composed of the conserved Trp 11 interacting with se veral aromatic residues. The two functional regions of Tat (basic and the c ysteine-rich regions) are well exposed to the solvent. A short a-helix is o bserved in region V adjacent to the basic region. This a helix induces loca l structural variations compared to the NMR structure of Tat Bra, and it br ings the cysteine-rich and basic regions closer. This study suggests that s imilar folding exists among Tat variants. (C) 2001 John Wiley & Sons, Inc.