Characterization of protein quality control components via dual reporter-containing misfolded cytosolic model substrates

• New substrates containing the enzymes Leu2 and firefly luciferase are introduced.
• LucLeu2myc and LucDMLeu2myc are subjected to Ubr1-dependent degradation.
• The Hsp70 chaperones of the Ssa-type are essential for the substrates' solubility.
• Chemiluminescence measurements allow the characterization of different Ssa functions.

Protein misfolding and protein aggregation are causes of severe diseases as neurodegenerative disorders, diabetes and cancer. Therefore, the cell has to constantly monitor the folding status of its proteome. Chaperones and components of the ubiquitin-proteasome system are key players in the cellular protein quality control process. In order to characterize components of the protein quality control system in a well-established model eukaryote - the yeast Saccharomyces cerevisiae - we established new cytosolic model substrates based on firefly luciferase and β-isopropylmalate dehydrogenase (Leu2). The use of these two different enzymes arranged in tandem as reporters enabled us to analyse the folding status and the degradation propensity of these new model substrates in yeast cells mutated in components of the cellular protein quality control system. The Hsp70 chaperone system known to be essential in the cellular protein quality control was chosen as a model for showing the high value of the luciferase-based model substrates in the characterization of components of the cytosolic protein quality control system in yeast.