FINE CHEMICAL MODIFICATIONS AT N-TERMINI AND C-TERMINI ENHANCE PEPTIDE PRESENTATION TO T-CELLS, BY INCREASING THE LIFE-SPAN OF BOTH FREE AND MHC-COMPLEXED PEPTIDES

We investigated the effect of modifying the N- and/or C-termini of the snake toxin peptide 24-36 on its presentation to T cells. Acetylation at the N-terminus as well as amidation at the C-terminus enhanced the capacity of the peptide to activate T cells. Simultaneous modificatio ns further increased the stimulating activity, the peptide becoming ap proximately 100-fold more potent than the unmodified peptide. Clearly, the introduced modifications increased the lifetime of the peptide fr ee in solution, by decreasing its proteolytic degradation, during the T cell stimulation assays. Paradoxically, however, at similar concentr ations of free peptides, the modified ones, especially those having an acetylated N-terminus, were much more active than the unmodified pept ide, irrespective of the experimental conditions. These observations s uggested that components other than protection from proteolytic degrad ation should be associated with the higher stimulating activities of t he modified peptides. Accordingly, chasing experiments with APC reveal ed that acetylation at N-terminus caused a higher persistence of the p eptides at APC surface. Together, our data indicate that (i) the T cel l stimulating capacity of a peptide is associated with its lifespans i n the free and MHC II bound states; and (ii) these lifespans can be gr eatly enhanced by introducing fine chemical modifications at N- and C- termini. These data may have some implications in designing more poten t peptidic immunomodulators.