Paper Title
Supramolecular Interactions in Peptides: Information on Their Physiochemical and Bioactivity

Abstract
The bioactivity and physiochemical properties of peptides rely on their sequence. Altering the amino acids of a peptide sequence cause new intramolecular and intermolecular supramolecular interactions. [1, 2]We have labeled the C-terminus of some homorepeat hexapeptides with Dbo, a fluorescent probe. [3]The fluorescence lifetime of Dbo in the peptides (τ) was measured as a function of pH. The side chains collide with Dbo intramolecularly and quench it efficiently only when they are deprotonated (i.e., pH ≥ side chain pKa). We outlined the pKa titration curve. By nonlinear fitting of the curve, we reported the average pKa of the peptides. We found out that charged repulsion between positively charged groups in His6–Dbo, Arg6–Dbo, and Lys6–Dbo –an intramolecular interaction–depresses the pKa value of the peptide's side chain. In another study, we fluorescently labeled either the C– or the N–terminus of ELAGIGILTV, an epitope peptide, with Nε-(5-carboxyfluorescein)-L-lysine. The affinity of the labeled peptides for human leukocyte antigen HLA-A*0201 on the surface of MCF-7 cells was extraordinarily increased. Our in silico modeling revealed specific binding sites for 5-carboxyfluorescein inside the HLA cavity. The strong binding owing to the supramolecular interaction between the labeled peptides and the HLA. Many studies have shown that increasing the affinity of an epitope peptide –for binding to its HLA– ends up in the immunogenicity of the epitope peptide. The obtained immunogenic peptide has the potential to be considered a peptide-based cancer vaccine. Keywords - Supramolecular Interaction, PKA Shift, Peptide, MHC-I, Fluorescent, MCF-7 Cell Line