Catalytically active peptides affected by self-assembly and residues order

Enzymes` efficiency and selectivity inspire developments in synthetic catalysis. Peptides are advantageous candidates for such catalytic systems owing to their ease of synthesis. Various studies aimed at mimicking the activity of serine proteases by designed peptides that present the catalytic site triad amino acids: serine, histidine and acidic residue. It has been proven that well-defined structures created by self-assembly of peptides or peptide derivatives have great influence on the catalytic activity. In this study we elucidate the effect of the triad residues order along β-sheet forming peptides sequence, on the catalytic activity using amphiphilic β-sheet motif. These motifs contain alternating hydrophobic and hydrophilic amino acids, with the residues Ser, His and Glu facing the hydrophilic side of the peptide. Three peptides denoted ssESH, ssEHS and ssHES (the one letter amino acids code represents the amino acids order along the peptide) were evaluated for their catalytic activity. The peptides at different concentrations (hence, different assembly states) were exposed to p-nitrophenyl acetate (pNPA), a model substrate molecule. The hydrolysis reaction of pNPA to acetate and p-nitrophenol (pNP) was followed spectroscopically at 400 nm. Further evaluation of the interactions between the peptides and the pNP/pNPA molecules was conducted by dialysis experiments. CD, ThT assays and TEM provided insight on the peptides` structures. The changes in the pKa of the amino acids Glu and His were also measured. Each peptide yielded a different catalytic efficiency value as function of concentration. We confirmed that the catalytic activity of the peptides is affected by the peptide’s supramolecular structure and the order of the amino acids on the surface. The peptide ssESH at concentration of 250 µM exhibited the greater catalytic activity.