Koc, Nicole: Controllable Thermoresponsive Protein Liquid-Liquid Phase Separation

Title: Controllable Thermoresponsive Protein Liquid-Liquid Phase Separation

Name: Nicole Koc

Major: Biological Sciences

School affiliation: School of Arts and Sciences

Programs: Honors College Capstone

Other contributors: Sagar Khare, Elliott Dolan, Aishwarya Kanchi Ranganath, Benjamin Schuster

Abstract: Low complexity domains (LCDs), such as the RGG domain, are sequences that are associated with the promotion of protein liquid liquid phase separation (LLPS). Regulatory factors such as temperature and salt concentration also modulate LLPS. Previous work has demonstrated controllable assembly of linearized RGG domains. Protein assemblies are sizable, well-organized supramolecular structures of individual proteins dictated by specific protein interactions contingent upon non-covalent and electrostatic interactions. Our work investigated how RGG domains, fused to assembly proteins, in a non linear fashion will affect phase separation properties. To determine the properties of LLPS-protein assemblies, we developed protein expression and purification protocols that enabled the recombinant proteins to remain soluble throughout the entire purification process, as these are difficult conditions to optimize. We performed spectrophotometric assays to measure temperature dependent turbidity. Spectrophotometric analysis indicated that two out of the three assemblies induced phase separation to occur at a higher temperature than its non assembly constituent parts. RGG fused protein assemblies elicit novel properties of phase separation by promoting droplet formation at increased temperatures that would previously render linearized RGG domains soluble. Becoming more proficient in conditions that affect protein LLPS can elucidate further elements about the exact mechanism behind it, which gives rise to numerous neurodegenerative diseases when this process erroneously occurs.