UBC Theses and Dissertations
Intracellular trafficking of a model polytopic membrane protein in Saccharomyces cerevisiae Dharwada, Sai Tejasvi
Polytopic membrane protein synthesis involves translation followed by translocation across the lipid bilayer at the ER. Here, various chaperones, together with enzymes that add post and co-translational modifications, help the protein achieve a final three-dimensional structure. General and substrate-specific chaperones prevent toxic aggregation of proteins by shielding and preventing interaction between non-native species. Terminally misfolded proteins are destroyed by the quality control machinery of the cell and the amino acids are recycled for further use. In the following study, we used Chitin synthase III (Chs3) of Saccharomyces cerevisiae as a model to dissect the complexities involved in polytopic membrane protein synthesis at the ER. Previous genetic screens from our lab have revealed a novel regulator of Chs3 trafficking called Pfa4, a DHHC enzyme required for Chs3 palmitoylation at the ER. At the ER, Chs3 also requires Chs7, a dedicated chaperone for folding and assembly. We identified a novel secondary role for Chs7 in Chs3 trafficking as a co-factor required for Chs3 function at the plasma membrane. Our study also examined the role of palmitoylation in Chs3 trafficking. Palmitoylation of Chs3 is required for its efficient interaction with Chs7, in addition to folding and ER export. A genome-wide screen also identified the Ubp3/Bre5 deubiquitination complex as a regulator of non-lipidated Chs3 degradation at the ER. The discovery that dedicated chaperones can take on additional roles and that palmitoylation can influence chaperone-client interactions could provide insights into the workings of the protein folding machinery at the ER.
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