CYTOTOXIC ACTIVITY OF THE AMINO-TERMINAL REGION OF HIV TYPE-1 NEF PROTEIN

Myristoylated 21- and 25-residue N-terminal peptides of the Nef protei n of HIV-1 lysed human erythrocytes and were cytotoxic toward a human CD4(+) T cell line, CEM, and primary human peripheral blood mononuclea r cells (PBMCs). The corresponding nonmyristoylated N-terminal peptide s were only very weakly hemolytic and cytotoxic. A myristoylated pepti de consisting of residues 31-50 of Nef was neither hemolytic nor cytot oxic. Alteration of the tryptophan residue at position 13 to a serine did not change the hemolytic and cytotoxic activity. Studies of the ul traviolet fluorescence of the tryptophan at position 5 in the peptide, using an artificial membrane system and fluorescence-quenching agents that inserted into the bilayer at different levels, suggested that my ristoylation results in this residue being brought into contact with t he upper hydrocarbon region of the lipid bilayer of the cell membrane. This tryptophan is flanked by a number of polar residues that would m aintain it in this position, resulting in a consider;able increase in disorder in the upper regions of the lipid bilayer, leading to its des tabilization and to Lysis. The cytotoxic activity of the myristoylated Nef fragments may, in part, explain the killing and deletion of cells , especially in lymphoid tissues, during HIV infection.