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Using a genetic screen we discovered that YGR198w (named YPP1), which is an essential Saccharomyces cerevisiae gene of unknown function, suppresses the toxicity of an α-synuclein (α-syn) mutant (A30P) that is associated with early onset Parkinson's disease. Here, we show that YPP1 suppresses lethality of A30P, but not of wild-type α-syn or the A53T mutant. The Ypp1 protein, when overexpressed, drives each of the three α-syns into vesicles that bud off the plasma membrane, but only A30P-containing vesicles traffick to and merge with the vacuole, where A30P is proteolytically degraded. We show that Ypp1p binds to A30P but not the other two α-syns; that YPP1 interacts with genes involved in endocytosis/actin dynamics (SLA1, SLA2, and END3), protein sorting (class E vps), and vesicle-vacuole fusion (MON1 and CCZ1) to dispose of A30P; and that YPP1 also participates in pheromone-triggered receptor-mediated endocytosis. Our data reveal that YPP1 mediates the trafficking of A30P to the vacuole via the endocytic pathway.

The mechanism by which the Parkinson’s disease-related protein α-synuclein (α-syn) causes neurodegeneration has not been elucidated. To determine the genes that protect cells from α-syn, we used a genetic screen to identify suppressors of the super sensitivity of the yeast Saccharomyces cerevisiae expressing α-syn to killing by hydrogen peroxide. Forty genes in ubiquitin-dependent protein catabolism, protein biosynthesis, vesicle trafficking and the response to stress were identified. Five of the forty genes—ENT3, IDP3, JEM1, ARG2 and HSP82—ranked highest in their ability to block α-syn-induced reactive oxygen species accumulation, and these five genes were characterized in more detail. The deletion of any of these five genes enhanced the toxicity of α-syn as judged by growth defects compared with wild-type cells expressing α-syn, which indicates that these genes protect cells from α-syn. Strikingly, four of the five genes are specific for α-syn in that they fail to protect cells from the toxicity of the two inherited mutants A30P or A53T. This finding suggests that α-syn causes toxicity to cells through a different pathway than these two inherited mutants. Lastly, overexpression of Ent3p, which is a clathrin adapter protein involved in protein transport between the Golgi and the vacuole, causes α-syn to redistribute from the plasma membrane into cytoplasmic vesicular structures. Our interpretation is that Ent3p mediates the transport of α-syn to the vacuole for proteolytic degradation. A similar clathrin adaptor protein, epsinR, exists in humans.

The neuronal protein alpha-synuclein (alpha-syn) has been suggested to be one of the factors linked to Parkinson's disease (PD). Several organisms, including the rat, mouse, worm, and fruit fly, are being used to study alpha-syn pathobiology. A new model organism was recently added to this armamentarium: the budding yeast Saccharomyces cerevisiae. The yeast system recapitulates many of the findings made with higher eukaryotes. For example, yeast cells expressing alpha-syn accumulate lipid droplets, have vacuolar/lysosomal defects, and exhibit markers of apoptosis, including the externalization of phosphatidylserine, the release of cytochrome c, and the accumulation of reactive oxygen species. This MiniReview focuses on the mechanisms by which alpha-syn induces oxidative stress and the mechanisms by which yeast cells respond to this stress. Three classes of therapeutics are discussed.

Mge1p is an essential nucleotide exchange factor, expressed by the budding yeast Saccharomyces cerevisiae, that catalyzes the release of ADP from Hsp70 molecules. Without such catalysis the Hsp70 reaction cycle comes to a halt. There is intriguing evidence that Mge1p and its homologues are more than just nucleotide exchange factors; specifically, these proteins may also be molecular thermosensors. In this study, a structure‐function analysis of Mge1p was conducted to ascertain the functional significance of the putative thermosensing domain of Mge1p, which comprises the first ˜66 N‐terminal residues of the protein. We show that (i) yeast cells that express Mge1p 66 exhibit a severe growth defect compared to cells expressing wt Mge1p; and (ii) preliminary results from a genetic screen reveal that mutating Ile102 to Asn in the Mge1p 66 protein partially restores cell growth. To further elucidate the role of the 66 N‐terminal residues, in the future we plan to isolate Mge1p 66 and variants that contain suppressor mutations and conduct biophysical studies that probe the binding of these proteins to mtHsp70.