(560d) Using a Peptide-Based Model System to Study Liquid to Solid Transitions of Membraneless Organelles

Liquid-liquid phase separated biological condensates, or membraneless organelles, are known to undergo liquid to solid phase transitions in certain disease states such as frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS). Polyelectrolyte complexes, formed by mixing of oppositely charged polymers, can form phase-separated liquid, or coacervate phases, as well as solid aggregates and can thus serve as model systems for studying liquid to solid phase transitions of membraneless organelles. Fine tuning of parameters that affect polyelectrolyte complexation that are also present in membraneless organelles, such as aromatic interactions and charge density, can be accomplished using peptide-based polyelectrolyte complex systems. In this study, the liquid coacervate forming system consisted of a polycation-polyanion peptide pair that had an alternating sequence of D-L chirality, as previous results illustrated that certain heterochiral sequence patterns can inhibit beta-sheet formation. Solid-aggregate forming polyelectrolyte complexes with D-L chirality were selected based on levels of hydrophobicity and beta-sheet formation. Addition of solid beta-sheet forming polyelectrolyte complexes to the liquid forming complex system resulted in a liquid-to-solid phase transition at different ratios of solid to liquid complex. Kinetics of the liquid-to-solid phase transition were investigated with Thioflavin-T, a benzathiole dye that fluoresces upon binding to beta-sheet structure containing fibrils.