Defining the pathways involved in spatial protein quality control in Saccharomyces cerevisiae

Abstract

Proteins need to be folded into specific three-dimensional conformations to be functional. An extensive network of factors, the protein quality control (PQC) machinery, ensures that the cell maintains a healthy proteome by coordinating their synthesis, folding, transport and degradation. A disruption in this machinery can lead to accumulation of protein aggregates, which is a hallmark of aging and many human pathologies. A key question in research on PQC is why and how certain aberrant proteins cause proteotoxicity, while others can be efficiently handled by the PQC. Sequestration of aggregates into larger inclusions and their deposition at distinct cellular sites have been suggested to be cytoprotective functions of spatial PQC. The articles included in this thesis use budding yeast to study spatial PQC in heat-stressed cells. Expanding the toolbox by a set of misfolding reporters and comparing their behavior revealed that diverse protein species are cleared at differential rates, even when residing in shared, intermixed protein inclusions. Using genome-wide screens, we pinpointed Sed5 and Sec7, major regulators of vesicle trafficking, as key factors controlling spatial PQC and disease protein detoxification. Electron microscopy of heat-stressed cells showed that aggregates localize predominantly in proximity to both mitochondria and virus-like particles. Our findings contribute to an increased understanding of three major features of spatial PQC: aggregate clearance, sequestration and intracellular location.