Understanding SNX-BAR protein structure and function in yeast

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Autophagy is the cellular process of removing aged or damaged components from the cell during routine cellular maintenance or during times of environmental stress such as starvation. The recycled by-products of autophagy can also be used to sustain critical metabolism for cell survival. Autophagy is conserved from yeast to humans and must be tightly controlled to prevent biological miscues that can result in aberrant cellular growth or death. The sorting nexins are a family of proteins that have been directly implicated in many aspects of autophagy, however the mechanism of their action there is poorly understood. This Project seeks to determine the regulatory elements that govern sorting nexin function during autophagy by determining the atomic structure and analyzing the function of a newly discovered sorting nexin. The Project will also provide graduate and undergraduate students an opportunity for training in biophysical and biochemical research. The Project will have an impact outside the laboratory by improving undergraduate curriculum through the development of novel 3D printing and Virtual Reality (VR) inquiry-based learning modules. In addition, the Project will create a course based undergraduate experience (CURE) centered on macromolecular structure and function. Overall, the broader impact will give scientists-in-training, including those from backgrounds underrepresented in STEM, an opportunity to enhance their scientific education.The sorting nexins (SNXs) constitute a diverse family of molecules that play varied roles in membrane trafficking, cell signaling, membrane remodeling and organelle motility. The SNX-BAR subfamily of the sorting proteins are typically thought to function in endosome sorting, but recently several have been shown to participate in autophagosome biogenesis. However, the mechanism of their role in autophagy is unclear. Prevailing models indicate that an evolutionarily conserved Phox-Homology (PX) domain, a feature common in all sorting nexins, binds specifically to phosphatidylinositol 3- phosphate (PI3P), the major lipid moiety of the endosome, to drive SNX-BAR function. The goal of this research is to understand the structure and function of a previously uncharacterized yeast SNX-BAR protein termed Vps501 and its interaction with the SEA complex that is involved in autophagy. Preliminary data suggests that Vps501 demonstrates a unique specificity for binding lipids and requires conformational changes to uniquely interact with the vacuole membrane. This Project will use a combination of biochemical, genetic and structural biology experiments to accomplish its goal. The Project will connect patterns of lipid specificity and structural characteristics in SNX-BAR proteins, while providing a new paradigm for understanding the relationship between the endo-vacuolar system and autophagy.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.