ACS Synth. Biol. https://doi.org/10.1021/acssynbio.0c00476 (2021)
Protein misfolding and aggregation can be harmful to cells, both in the context of disease and during heterologous expression for biotechnological applications, where it also limits the production yields of desired compounds. To facilitate detection and screening of aggregation-prone proteins in yeast, Romero-Suarez et al. developed a fluorescence-based reporter of aggregated proteins based on promoters involved in the unfolded protein response (UPR). By screening the proteome for gene products that were highly upregulated upon expression of a poorly folded, insoluble protein (lipomycin polyketide synthase) compared to expression of the well-folded maltose-binding protein, the authors identified a suite of promoters associated with the yeast UPR. Further characterization of these promoters, along with engineering of their upstream activating sequence copy numbers and the associated fluorescent protein output, culminated in the development of an optimized reporter system that responds to increasing levels of insoluble protein, whether due to the inherent qualities of a protein or to chemical induction of aggregation by a proteasome inhibitor. This reporter can also be used in a FACS-based screen for isolation of cells expressing high levels of soluble protein. The availability of such a method to rapidly identify cells with especially high or low levels of unfolded protein could facilitate future studies of disease-relevant aggregation-prone proteins and identification of biotechnologically useful variants.
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