Sequence-Specific Resonance Assignments of the ¹H-NMR Spectra of a Synthetic, Biologically Active EIAV Tat Protein

The equine infectious anemia virus (EIAV) trans-activating (Tat) protein is a close homologue of the human immunodeficiency virus (HIV) Tat protein. Both of these proteins bind to an RNA trans-activation responsive element (TAR). We synthesized chemically a protein with the sequence of the 75 amino acid Tat protein from EIAV. The chemically synthesized protein was shown to be biologically active. Circular dichroism (CD) and ¹H nuclear magnetic resonance (NMR) spectroscopy were used to structurally characterize the synthetic protein. We obtained nearly complete resonance assignments in the 2D-NMR spectra of the protein at pH 3.0. There is at least some evidence from the experimental data that the basic TAR binding domain of the synthetic protein has a tendency to form a helix, but our experiments also indicate that the protein probably does not have an overall stable tertiary structure in aqueous solution at this pH. CD spectroscopy suggested that the protein adopts a more stable, predominantly α-helical structure in a trifluoroethanol/water solution.