CAREER: PolyQ Proteins Phase Transition Induced by Lipid Vesicles

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The structure-function paradigm states that protein structure dictates function. However, this concept has been challenged by recent discoveries that ~40% of proteins in eukaryotic cells with important biological functions lack a stable three-dimensional (3D) structure. Many of these intrinsically disordered proteins (IDPs) can condense into membraneless liquid-like or gel-like assemblies through a process termed phase transition. Formation of these assemblies enriches these proteins within an isolated microenvironment, and thus regulates their biological activities. At present, it remains a mystery how the ultrastructure of phase transition assemblies supports spatiotemporal control of functions of the enclosed proteins. Due to their structural flexibility, IDPs present inherent challenges for experimental structural studies. By applying state-of-the-art structural methods, namely cryo-electron tomography (cryoET) and advanced subtomogram analyses, this project will reveal the architecture of phase transition assemblies, and establish a connection between the 3D structure, dynamics, and function for this important class of proteins. Overall, this project will contribute towards a more complete structure-function paradigm in fundamental biology. In parallel, the PI will develop a research-driven education curriculum that introduces interdisciplinary research to undergraduate students, promotes interactive graduate student teaching, and provides engaging online training resources on cutting-edge cryoET biostructure imaging to young scholars. Development of the cryoET educational portal has broader impacts. It will showcase to the general public the exciting potential of this novel bioimaging technique for unraveling dynamic biological processes in nature.The goal of this project is to resolve the structural organization of protein phase transition assemblies to provide a deeper understanding of how biophysical and structural properties of these assemblies support biological activities of enclosed IDPs. Proteins with extended polyglutamine (polyQ) homo-repeats represent one of the simplest IDPs. Using this system, the PI will resolve, at the subnanometer level, the 3D structural organization of phase transition assemblies formed under physiologically relevant experimental conditions. This project will also investigate how the formation, stability, and aggregation propensity of phase transition assemblies are affected by sequence characteristics of the IDPs and lipid vesicles. This work will advance our understanding of the molecular mechanisms underlying IDP phase transitions. More importantly, results from this work will facilitate development of strategies for regulating these metastable assemblies and thereby modulating protein homeostasis in cells.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.