LAUSR

Abstract The effects of arginine residues in peptide sequences on their specific acid-base properties were investigated. Two short original fragments of the human Pin1 WW domain (hPin1 14–24; hPin1 15–23) and one single point mutation system (the original charged Lys14 and Tyr24 residues were replaced with nonpolar alanine residues) derived from hPin1 were considered. The amino acid composition controls to a large extent the process of folding and thus regulates the functions of the entire system. The specific behavior of arginine residues presented in the investigated peptides in a solution is directly reflected in their abnormally low values of pKa as compared to those of the reference compound. This phenomenon seems to result from the formation of aggregates within the system by the guanidine forms present in the Arg sidechains. The acid-base properties of the investigated peptides show that under physiological conditions, the charge of these systems is close to 2. Summarizing, the analysis of interactions between peptides and biologically important structures and membranes should consider cationic forms of peptides.