Exploring the Tunability of the Aggregation and Gelation Process of the Tripeptide Gag

Self-assembly of biomolecules is an important issue explored in biomedical, biophysical, and bio-material research. Understanding how and why certain peptides/proteins favor to self-assemble into larger networks can reveal the mechanism of amyloid formation and assist in bottom-up designs of supramolecular structures. Various low molecular weight di- and tripeptides with aromatic residues and terminal groups have been shown to form hydrogels. Contrary to expectations, we originally discovered that the cationic tripeptide with low hydrophobicity, glycyl-alanyl-glycine (GAG), forms a gel in 55 mol% ethanol/45 mol% if the concentration exceeds 200mM. The underlying structure does not exhibit the canonical β-sheet structure markers yet is comprised of unusually long crystalline fibrils in the 10−5m range. Rheological data and vibrational circular dichroism spectra suggest the existence of two different gel phases, one formed between 15° and 35°C with left handed twisted fibrils and G’ values at ca. 2∗104 Pa and another one formed below 15°C with right handed twisted fibrils and G’ values close to 105 Pa. Results from DFT calculations indicate that the two phases might be underlied by differently structured fibrils. Knowing that by simply changing temperature can lead to different underlying structures, rheological strength, and melt point, we have begun constructing a three dimension phase diagram by altering the temperature, peptide concentration, and mol fraction of ethanol to see precisely how these external parameters alter the gel itself. Using electronic circular dichroism and fluorescence, it has been observed that by lowering the formation temperature, the fibrils form much quicker compared to room temperature, but the resulting melting temperatures also decrease. Furthermore, we hyposthesize that the ethanol fraction is more imperative than the peptide concentration when it comes to aggregation and subsequent gelation of the sample based on preliminary results.