Collaborative Research: Integrating Theory and Experiment to Unravel Protein Transport in the ER

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The endoplasmic reticulum, or ER, is a specialized intracellular structure responsible for a myriad of critical cellular functions, including protein synthesis, quality-control, and export. It is estimated that about one third of all mammalian proteins are created and then exported from the ER as the first step on their way to being secreted from the cell to become the signal carriers and receptors that interface with the extracellular world. The ER itself forms an interconnected network of sheets and hollow tubules that hosts a variety of protein processing pathways. This project aims to address a fundamental question in cell biology -- how does the structural complexity of the ER regulate and support its functional role as the protein processing hub of the cell? An interdisciplinary approach combines imaging within live cells, predictive physical modeling, and state-of-the-art simulation and data-analysis techniques to explore how proteins navigate through the ER maze. This collaborative effort seeks to unravel how the unique physical structure of the ER regulates its critical biological functions of protein sorting and export. The Broader Impacts of this work includes the intrinsic merit of the research as all eukaryotic cells have ER and dysfunctions of this organelles have been implicated in such human afflictions as diabetes and Parkinson’s disease. Additionally, the work will be integrated with a broad interdisciplinary educational program that spans from an elementary school science club, to a high school robotics team, to undergraduate research interns, aiming to introduce students at all educational levels to the insights that may be gained by applying physical and mathematical approaches to biological problems.The endoplasmic reticulum forms a continuous polymorphic network of stacked sheets and hollow tubules that spans throughout the intracellular space and is responsible for the folding, quality-control, sorting, and export of secreted proteins. The primary goal of this project is to establish a structure-function relationship for this organelle, developing a quantitative understanding of how its unique morphology supports its role as a protein delivery network. This goal will be approached collaboratively from the dual perspectives of physical model-building and dynamic live-cell imaging. A mathematical framework will be developed that combines analytical results for reaction-diffusion processes in complex geometries with novel simulation techniques to establish how network morphology modulates the kinetics of proteins finding binding partners, sorting regions, and exit sites within the network. Rapid confocal imaging of ER structure and photoactivated luminal and membrane proteins will enable quantification of the underlying dynamics of network structures (including tubule junctions and exit sites) and the embedded proteins. Genetic and pharmacological perturbations will be leveraged to test predictions of the effect of structure on intra-ER protein transport. The efficiency of protein sorting and export from the ER will be quantified using a synchronized accumulation-and-release system, and the contribution of physical factors such as bulk luminal flow and exit site distribution will be explored through a confluence of theoretical models and live-cell measurements. Ultimately, a feedback loop between theory and experiment will elucidate the underlying principles that link the complex architecture of the ER with its crucial protein processing functions.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.