Inhibition of HIV derived lentiviral production by TAR RNA binding domain of TAT protein

Attenuating HIV Tat/TAR-mediated protein expression by exploring the side chain length of positively charged residues

RNA is a drug target involved in diverse cellular functions and viral processes. Molecules that inhibit the HIV TAR RNA-Tat protein interaction may attenuate Tat/TAR-dependent protein expression and potentially serve as anti-HIV therapeutics. By incorporating positively charged residues with mixed side chain lengths, we designed peptides that bind TAR RNA with enhanced intracellular activity. Tat-derived peptides that were individually substituted with positively charged residues with varying side chain lengths were evaluated for TAR RNA binding. Positively charged residues with different side chain lengths were incorporated at each Arg and Lys position in the Tat-derived peptide to enhance TAR RNA binding. The resulting peptides showed enhanced TAR RNA binding affinity, cellular uptake, nuclear localization, proteolytic resistance, and inhibition of intracellular Tat/TAR-dependent protein expression compared to the parent Tat-derived peptide with no cytotoxicity. Apparently, the enhanced inhibition of protein expression by these peptides was not determined by RNA binding affinity, but by proteolytic resistance. Despite the high TAR binding affinity, a higher binding specificity would be necessary for practical purposes. Importantly, altering the positively charged residue side chain length should be a viable strategy to generate potentially useful RNA-targeting bioactive molecules.

Using peptides to study the interaction between the p53 tetramerization domain and HIV-1 Tat

Peptides are valuable tools for studying protein-protein interactions, especially in cases of isolated protein domains and natively unfolded proteins. Here, we used peptides to quantitatively characterize the interaction between the natively unfolded HIV-1 Tat protein and the tetramerization domain of the cellular tumor suppressor protein p53. We used peptide mapping, fluorescence anisotropy, and NMR spectroscopy to perform a detailed structural and biophysical characterization of the interaction between the two proteins and elucidate its molecular mechanism, which have so far been studied using cell-based methods. We show that the p53 tetramerization domain, p53(326-355), binds directly to residues 1-35 and 47-57 in Tat. We have characterized the interaction between p53(326-355) and Tat(47-57) in detail. The p53 residues that are mainly involved in binding to Tat(47-57) are E343 and E349, which bind to the positively charged arginine-rich motif of Tat by a partly electrostatic mechanism. All oligomerization states of p53(326-355) bind Tat(47-57) without inhibiting p53 tetramerization, since the residues in p53(326-355) that bind Tat(47-57) face away from the tetramerization interface. We conclude that p53 is able to bind Tat as a transcriptionally active tetramer.

The taming of the cell penetrating domain of the HIV Tat: myths and realities

Protein transduction with cell penetrating peptides over the past several years has been shown to be an effective way of delivering proteins in vitro and now several reports have also shown valuable in vivo applications in correcting disease states. An impressive bioinspired phenomenon of crossing biological barriers came from HIV transactivator Tat protein. Specifically, the protein transduction domain of HIV Tat has been shown to be a potent pleiotropic peptide in protein delivery. Various approaches such as molecular modeling, arginine guanidinium head group structural strategy, multimerization of PTD sequence and phage display system have been applied for taming of the PTD. This has resulted in identification of PTD variants which are efficient in cell membrane penetration and cytoplasmic delivery. In spite of these state of the art technologies, the dilemma of low protein transduction efficiency and target specific delivery of PTD fusion proteins remains unsolved. Moreover, some misconceptions about PTD of Tat in the literature require considerations. We have assembled critical information on secretory, plasma membrane penetration and transcellular properties of Tat and PTD using molecular analysis and available experimental evidences.