Phosphatidylinositol 3-phosphate metabolism impacts cellular α-Synuclein localisation in Saccharomyces cerevisiae.

Alpha-Synuclein (αSyn), a hallmark protein of synucleinopathies such as Parkinson's disease, is likely to be involved in neuronal membrane trafficking and synaptic vesicle dynamics at axon terminals. Its specific binding to anionic phospholipids, such as phosphatidylinositol phosphates (PIPs) that are essential for intracellular signaling and membrane trafficking, suggests an involvement in vesicular transport processes. In Saccharomyces cerevisiae, a model organism for cell biological PD research, human αSyn localises to the plasma membrane via the secretory machinery. Employing this yeast model, we investigated the impact of αSyn on cellular quality control mechanisms. Additionally, we focused on the effect of αSyn expression in yeast mutants impaired in specific phospholipid biosynthesis and transport pathways, including endo-vacuolar trafficking and autophagy. In the deletion strains vps34Δ and vps15Δ, lacking PI3P biosynthesis, αSyn mislocalises in the cytosol, and significantly reduces cell viability. In these strains, αSyn species containing an intact lipid-binding N-terminus also form large peri-vacuolar, lipid-rich accumulations. In wild-type cells, αSyn expression alters the morphology of PI3P-rich membrane structures and upregulates transcription of SEC4, which encodes a key regulator of the late secretory pathway. Moreover, αSyn co-localises with overexpressed Sec4 at the emerging cell bud. Our findings demonstrate that PI3P is critical for the targeting of αSyn to the yeast plasma membrane via the secretory pathway, revealing a potential entry point into this complex machinery. Understanding the relationship between αSyn and vesicular trafficking in this system will enhance our knowledge of αSyn-trafficking in mammalian cells and, eventually, in PD, offering new research avenues.