Experimental determination of binodal compositions of protein and peptide solutions

Biomacromolecules such as proteins are known to undergo liquid-liquid phase separation to a dense phase and a dilute phase under certain conditions of temperature, pH, salt and protein concentrations. As the study of proteins is complex due to their zwitterionic nature, hydrogen bonding, inclusion of hydrophobic side chains, pi-cation interactions and presence of metal binding and folded domains, we will study in parallel both a protein, FUS, and simplified peptides of known sequences.
We will present quantitative measurements of both branches of the binodal curves of the phase diagrams obtained via quantitative phase imaging microscopy for the protein FUS and simpler peptide sequences. As the tyrosine-arginine interactions are believed to play a significant role in inter-molecular association, we shall examine the variation of the branches as FUS tyrosines are alterned to phenylalanines and 3,4-dihydroxy-L-phenylalanines imparting changes in hydrogen bonding and pi-cation interaction strength. In the case of peptides, we will examine how multiplicity of pi-cation interactions at constant density of tyrosines and arginines affects the associations and thus the phase diagram.