Structure-activity relationship study of the plasma membrane translocating potential of a short peptide from HIV-1 Tat protein

Tat, a 86-amino acid protein involved in the replication of Human Immunodeficiency Virus type 1 (HIV-I), is able to translocate efficiently through the plasma membrane and to reach the nucleus to transactivate the viral genome. The region 37-72 of the Tat protein, centered on a cluster of basic amino acids, has been assigned to this translocation activity. Recent data in our group have attributed this membrane translocating activity to a peptide extending from residues 48 to 60, which contains a cluster of eight basic amino acids within a linear sequence of nine residues. Internalization of this peptide into cells occurred within minutes at concentrations as low as 100 nM. In order to define more precisely the involvement of these basic amino acids in peptide translocation, several analogues carrying deletions or substitutions of one, or several, of the basic residues were synthesized and tested for their cellular uptake and nuclear translocation. A direct correlation between the overall charge of the peptide and its cell internalization was found. In addition, the covalent linkage of this short basic peptide allows the efficient translocation of a non-membrane permeant peptide.