Genome-wide screen identifies new set of genes for improved heterologous laccase expression in Saccharomyces cerevisiae

Abstract

The yeast Saccharomyces cerevisiae is widely used as a host cell for recombinant protein production due to its fast growth, cost-effective culturing, and ability to secrete large and complex proteins. However, one major drawback is the relatively low yield of produced proteins compared to other host systems. To address this issue, we developed an overlay assay to screen the yeast knockout collection and identify mutants that enhance recombinant protein production, specifically focusing on the secretion of the Trametes trogii fungal laccase enzyme. Gene ontology analysis of these mutants revealed an enrichment of processes including vacuolar targeting, vesicle trafficking, proteolysis, and glycolipid metabolism. We confirmed that a significant portion of these mutants also showed increased activity of the secreted laccase when grown in liquid culture. Notably, we found that the combination of deletions of OCA6, a tyrosine phosphatase, along with PMT1 or PMT2, two ER membrane protein-O-mannosyltransferases involved in ER quality control, and SKI3, a component of the SKI complex responsible for mRNA degradation, further increased secreted laccase activity. Conversely, we also identified over 200 gene deletions that resulted in decreased secreted laccase activity, including many genes that encode for mitochondrial proteins and components of the ER-associated degradation pathway. Intriguingly, the deletion of the ER DNAJ co-chaperone SCJ1 led to almost no secreted laccase activity. When we expressed SCJ1 from a low-copy plasmid, laccase secretion was restored. However, overexpression of Scj1p had a detrimental effect, indicating that precise dosing of key chaperone proteins is crucial for optimal recombinant protein expression. ImportanceOur study showcases a newly developed high throughput screening technique to identify yeast mutant strains that exhibit an enhanced capacity for recombinant protein production. Using a genome-wide approach, we show that vesicle trafficking plays a crucial role in protein production, as the genes associated with this process are notably enriched in our screen. Furthermore, we demonstrate that a specific set of gene deletions, which were not previously recognized for their impact on recombinant laccase production, can be effectively manipulated in combination to increase the production of heterologous proteins. This study offers potential strategies for enhancing the overall yield of recombinant proteins and provides new avenues for further research in optimizing protein production systems.