Abstract
BackgroundThe yeast Saccharomyces cerevisiae provides intriguing possibilities for synthetic biology and bioprocess applications, but its use is still constrained by cellular characteristics that limit the product yields. Considering the production of advanced biopharmaceuticals, a major hindrance lies in the yeast endoplasmic reticulum (ER), as it is not equipped for efficient and large scale folding of complex proteins, such as human antibodies.ResultsFollowing the example of professional secretory cells, we show that inducing an ER expansion in yeast by deleting the lipid-regulator gene OPI1 can improve the secretion capacity of full-length antibodies up to fourfold. Based on wild-type and ER-enlarged yeast strains, we conducted a screening of a folding factor overexpression library to identify proteins and their expression levels that enhance the secretion of antibodies. Out of six genes tested, addition of the peptidyl-prolyl isomerase CPR5 provided the most beneficial effect on specific product yield while PDI1, ERO1, KAR2, LHS1 and SIL1 had a mild or even negative effect to antibody secretion efficiency. Combining genes for ER enhancement did not induce any significant additional effect compared to addition of just one element. By combining the Δopi1 strain, with the enlarged ER, with CPR5 overexpression, we were able to boost the specific antibody product yield by a factor of 10 relative to the non-engineered strain.ConclusionsEngineering protein folding in vivo is a major task for biopharmaceuticals production in yeast and needs to be optimized at several levels. By rational strain design and high-throughput screening applications we were able to increase the specific secreted antibody yields of S. cerevisiae up to 10-fold, providing a promising strain for further process optimization and platform development for antibody production.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0488-5) contains supplementary material, which is available to authorized users.
Highlights
The yeast Saccharomyces cerevisiae provides intriguing possibilities for synthetic biology and bioprocess applications, but its use is still constrained by cellular characteristics that limit the product yields
unfolded protein response (UPR) leads to endoplasmic reticulum (ER) expansion, in yeast it has been shown that increasing ER size alone is sufficient to alleviate conformational stress independently from chaperone levels and UPR-induction [15]
Increase in ER size is a characteristic feature of professional secretory cell development [32, 33] and has been stated to reduce ER stress in S. cerevisiae [15], we decided to study whether increasing ER size before induction of protein production would correlate with an increased IgG yield in our system
Summary
The yeast Saccharomyces cerevisiae provides intriguing possibilities for synthetic biology and bioprocess applications, but its use is still constrained by cellular characteristics that limit the product yields. The yeast endoplasmic reticulum (ER) is limited in its recombinant protein folding capacity, and is an important target for cell engineering to improve product yields [5, 6]. Producing recombinant proteins in yeast de Ruijter et al Microb Cell Fact (2016) 15:87 often leads to accumulation of folding intermediates in the ER and to induction of the unfolded protein response (UPR) [7]. UPR leads to ER expansion, in yeast it has been shown that increasing ER size alone is sufficient to alleviate conformational stress independently from chaperone levels and UPR-induction [15]. The development of secretory cells employs some of the same molecular routes as the UPR and has similar effects on gene expression, the onset of protein production is preceded by ER expansion [20].
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