Enhanced cell-surface display of a heterologous protein using SED1 anchoring system in SED1-disrupted Saccharomyces cerevisiae strain

Strategic approaches for designing yeast strains as protein secretion and display platforms

Yeast has been established as a versatile platform for expressing functional molecules, owing to its well-characterized biology and extensive genetic modification tools. Compared to prokaryotic systems, yeast possesses advanced cellular mechanisms that ensure accurate protein folding and post-translational modifications. These capabilities are particularly advantageous for the expression of human-derived functional proteins. However, designing yeast strains as an expression platform for proteins requires the integration of molecular and cellular functions. By delving into the complexities of yeast-based expression systems, this review aims to empower researchers with the knowledge to fully exploit yeast as a functional platform to produce a diverse range of proteins. This review includes an exploration of the host strains, gene cassette structures, as well as considerations for maximizing the efficiency of the expression system. Through this in-depth analysis, the review anticipates stimulating further innovation in the field of yeast biotechnology and protein engineering.

Engineering Saccharomyces boulardii for enhanced surface display capacity

Saccharomyces boulardii (Sb) has gained significant attention for its potential therapeutic application as a probiotic yeast strain. Current approaches often leverage its secretion and display capabilities to deliver therapeutic agents aimed at alleviating intestinal disorders. However, relatively few studies have focused on optimizing its display efficiency. In this study, we evaluated two surface display systems, Aga2- and Sed1-based, for use in Sb by systematically modifying display cassette components and the host strain. Initially, both systems were tested in Saccharomyces cerevisiae (Sc) and Sb to validate their design. Sc consistently outperformed Sb in both display expression and efficiency, highlighting the need for further optimization in Sb. To enhance the display efficiency in Sb, we investigated specific modifications to the display cassette, including the use of linker sequences for Aga2 and variations in anchor length for Sed1. These experiments identified key factors influencing display performance. Subsequently, we engineered a modified Sb strain, LIP02, by overexpressing AGA1 and deleting cell wall-related genes (CCW12, CCW14, and FYV5). These modifications were expected to expand the available docking sites for the protein of interest (POI) and improve overall protein secretion and display efficiency. As a result, the modified strain exhibited a significant enhancement in display capacity compared to the wild-type Sb strain. Furthermore, genome integration of the display cassette in LIP02 enhanced both stability and expression compared to plasmid-based systems. Importantly, the functionality of β-glucosidase displayed on LIP02 was preserved, as demonstrated by improved enzymatic activity and robust growth on cellobiose as the sole carbon source. These findings establish LIP02 as a superior host for surface display applications in Sb, offering a more stable and efficient platform for the expression of therapeutic proteins and other functional biomolecules.

Advancing cellulose utilization and engineering consolidated bioprocessing yeasts: current state and perspectives

Despite the lack of implementation of consolidated bioprocessing (CBP) at an industrial scale, this bioconversion strategy still holds significant potential as an economically viable solution for converting lignocellulosic biomass (LCB) into biofuels and green chemicals, provided an appropriate organism can be isolated or engineered. The use of Saccharomyces cerevisiae for this purpose requires, among other things, the development of a cellulase expression system within the yeast. Over the past three decades, numerous studies have reported the expression of cellulase-encoding genes, both individually and in combination, in S. cerevisiae. Various strategies have emerged to produce a core set of cellulases, with differing degrees of success. While one-step conversion of cellulosic substrates to ethanol has been reported, the resulting titers and productivities fall well below industrial requirements. In this review, we examine the strategies employed for cellulase expression in yeast, highlighting the successes in developing basic cellulolytic CBP-enabled yeasts. We also summarize recent advancements in rational strain design and engineering, exploring how these approaches can be further enhanced through modern synthetic biology tools to optimize CBP-enabled yeast strains for potential industrial applications. KEY POINTS: • S. cerevisiae's lack of cellulolytic ability warrants its engineering for industry. • Advancements in the expression of core sets of cellulases have been reported. • Rational engineering is needed to enhance cellulase secretion and strain robustness. • Insights gained from omics strategies will direct the future development of CBP strains.

Engineering Saccharomyces cerevisiae for application in integrated bioprocessing biorefineries

After decades of research and development, no organism - natural or engineered - has been described that can produce commodity products through direct microbial conversion to meet industry demands in terms of rates and yields. Variation in lignocellulosic biomass (LCB) feedstocks, the lack of a widely applicable pretreatment method, and the limited economic value of energy products further complicates second-generation biofuel production. Nevertheless, the emergence of advanced genomic editing tools and a more comprehensive understanding of yeast metabolic systems offer promising avenues for the creation of yeast strains tailored to LCB biorefineries. Here, we discuss recent advances toward developing yeast strains that could convert different LCB fractions into a series of economically viable commodity products in a biorefinery.

Saccharomyces cerevisiae cell surface display technology: Strategies for improvement and applications

Microbial cell surface display technology provides a powerful platform for engineering proteins/peptides with enhanced properties. Compared to the classical intracellular and extracellular expression (secretion) systems, this technology avoids enzyme purification, substrate transport processes, and is an effective solution to enzyme instability. Saccharomyces cerevisiae is well suited to cell surface display as a common cell factory for the production of various fuels and chemicals, with the advantages of large cell size, being a Generally Regarded As Safe (GRAS) organism, and post-translational processing of secreted proteins. In this review, we describe various strategies for constructing modified S. cerevisiae using cell surface display technology and outline various applications of this technology in industrial processes, such as biofuels and chemical products, environmental pollution treatment, and immunization processes. The approaches for enhancing the efficiency of cell surface display are also discussed.

Genetic manipulation strategies for ethanol production from bioconversion of lignocellulose waste

Lignocellulose waste was served as promising raw material for bioethanol production. Bioethanol was considered to be a potential alternative energy to take the place of fossil fuels. Lignocellulosic biomass synthesized by plants is regenerative, sufficient and cheap source for bioethanol production. The biotransformation of lignocellulose could exhibit dual significance-reduction of pollution and obtaining of energy. Some strategies are being developing and increasing the utilization of lignocellulose waste to produce ethanol. New technology of bioethanol production from natural lignocellulosic biomass is required. In this paper, the progress in genetic manipulation strategies including gene editing and synthetic genomics for the transformation from lignocellulose to ethanol was reviewed. At last, the application prospect of bioethanol was introduced.

Yeast Surface Display System: Strategies for Improvement and Biotechnological Applications

Yeast surface display (YSD) is a “whole-cell” platform used for the heterologous expression of proteins immobilized on the yeast’s cell surface. YSD combines the advantages eukaryotic systems offer such as post-translational modifications, correct folding and glycosylation of proteins, with ease of cell culturing and genetic manipulation, and allows of protein immobilization and recovery. Additionally, proteins displayed on the surface of yeast cells may show enhanced stability against changes in temperature, pH, organic solvents, and proteases. This platform has been used to study protein-protein interactions, antibody design and protein engineering. Other applications for YSD include library screening, whole-proteome studies, bioremediation, vaccine and antibiotics development, production of biosensors, ethanol production and biocatalysis. YSD is a promising technology that is not yet optimized for biotechnological applications. This mini review is focused on recent strategies to improve the efficiency and selection of displayed proteins. YSD is presented as a cutting-edge technology for the vectorial expression of proteins and peptides. Finally, recent biotechnological applications are summarized. The different approaches described herein could allow for a better strategy cascade for increasing protein/peptide interaction and production.

Contemporary proteomic research on lignocellulosic enzymes and enzymolysis: A review

This review overviewed the current researches on the isolation of novel strains, the development of novel identification protocols, the key enzymes and their synergistic interactions with other functional enzyme systems, and the strategies for enhancing enzymolysis efficiencies. The main obstacle for realizing biorefinery of lignocellulosic biomass to biofuels or biochemicals is the high cost of enzymolysis stage. Therefore, research prospects to reduce the costs for lignocellulose hydrolysis were outlined.

Resveratrol production from several types of saccharide sources by a recombinant Scheffersomyces stipitis strain

Resveratrol is a plant-derived aromatic compound with a wide range of beneficial properties including antioxidant and anti-aging effects. The resveratrol currently available on the market is predominantly extracted from certain plants such as grape and the Japanese knotweed Polygonum cuspidatum. Due to the unstable harvest of these plants and the low resveratrol purity obtained, it is necessary to develop a stable production process of high-purity resveratrol from inexpensive feedstocks. Here, we attempted to produce resveratrol from a wide range of sugars as carbon sources by a using the genetically-engineered yeast Scheffersomyces stipitis (formerly known as Pichia stipitis), which possesses a broad sugar utilization capacity. First, we constructed the resveratrol producing strain by introducing genes coding the essential enzymes for resveratrol biosynthesis [tyrosine ammonia-lyase 1 derived from Herpetosiphon aurantiacus (HaTAL1), 4-coumarate: CoA ligase 2 derived from Arabidopsis thaliana (At4CL2), and stilbene synthase 1 derived from Vitis vinifera (VvVST1)]. Subsequently, a feedback-insensitive allele of chorismate mutase was overexpressed in the constructed strain to improve resveratrol production. The constructed strain successfully produced resveratrol from a broad range of biomass-derived sugars [glucose, fructose, xylose, N-acetyl glucosamine (GlcNAc), galactose, cellobiose, maltose, and sucrose] in shake flask cultivation. Significant resveratrol titers were detected in cellobiose and sucrose fermentation (529.8 and 668.6 mg/L after 120 h fermentation, respectively), twice above the amount obtained with glucose (237.6 mg/L). Metabolomic analysis revealed an altered profile of the metabolites involved in the glycolysis and shikimate pathways, and also of cofactors and metabolites of energy metabolisms, depending on the substrate used. The levels of resveratrol precursors such as L-tyrosine increased in cellobiose and sucrose-grown cells. The results indicate that S. stipitis is an attractive microbial platform for resveratrol production from broad types of biomass-derived sugars and the selection of suitable substrates is crucial for improving resveratrol productivity of this yeast.

Heterologous production of cellulose- and starch-degrading hydrolases to expand Saccharomyces cerevisiae substrate utilization: Lessons learnt

Selected strains of Saccharomyces cerevisiae are used for commercial bioethanol production from cellulose and starch, but the high cost of exogenous enzymes for substrate hydrolysis remains a challenge. This can be addressed through consolidated bioprocessing (CBP) where S. cerevisiae strains are engineered to express recombinant glycoside hydrolases during fermentation. Looking back at numerous strategies undertaken over the past four decades to improve recombinant protein production in S. cerevisiae, it is evident that various steps in the protein production "pipeline" can be manipulated depending on the protein of interest and its anticipated application. In this review, we briefly introduce some of the strategies and highlight lessons learned with regards to improved transcription, translation, post-translational modification and protein secretion of heterologous hydrolases. We examine how host strain selection and modification, as well as enzyme compatibility, are crucial determinants for overall success. Finally, we discuss how lessons from heterologous hydrolase expression can inform modern synthetic biology and genome editing tools to provide process-ready yeast strains in future. However, it is clear that the successful expression of any particular enzyme is still unpredictable and requires a trial-and-error approach.

Improving the functionality of surface-engineered yeast cells by altering the cell wall morphology of the host strain

The expression of functional proteins on the cell surface using glycosylphosphatidylinositol (GPI)-anchoring technology is a promising approach for constructing yeast cells with special functions. The functionality of surface-engineered yeast strains strongly depends on the amount of functional proteins displayed on their cell surface. On the other hand, since the yeast cell wall space is finite, heterologous protein carrying capacity of the cell wall is limited. Here, we report the effect of CCW12 and CCW14 knockout, which encode major nonenzymatic GPI-anchored cell wall proteins (GPI-CWPs) involved in the cell wall organization, on the heterologous protein carrying capacity of yeast cell wall. Aspergillus aculeatus β-glucosidase (BGL) was used as a reporter to evaluate the protein carrying capacity in Saccharomyces cerevisiae. No significant difference in the amount of cell wall-associated BGL and cell-surface BGL activity was observed between CCW12 and CCW14 knockout strains and their control strain. In contrast, in the CCW12 and CCW14 co-knockout strains, the amount of cell wall-associated BGL and its activity were approximately 1.4-fold higher than those of the control strain and CCW12 or CCW14 knockout strains. Electron microscopic observation revealed that the total cell wall thickness of the CCW12 and CCW14 co-knockout strains was increased compared to the parental strain, suggesting a potential increase in heterologous protein carrying capacity of the cell wall. These results indicate that the CCW12 and CCW14 co-knockout strains are a promising host for the construction of highly functional recombinant yeast strains using cell-surface display technology. KEY POINTS: • CCW12 and/or CCW14 of a BGL-displaying S. cerevisiae strain were knocked out. • CCW12 and CCW14 co-disruption improved the display efficiency of BGL. • The thickness of the yeast cell wall was increased upon CCW12 and CCW14 knockout.

Cell-surface engineering of yeasts for whole-cell biocatalysts

Due to the unique advantages comparing with traditional free enzymes and chemical catalysis, whole-cell biocatalysts have been widely used to catalyze reactions effectively, simply and environment friendly. Cell-surface display technology provides a novel and effective approach for improved whole-cell biocatalysts expressing heterologous enzymes on the cell surface. They can overcome the substrate transport limitation of the intracellular expression and provide the enzymes with enhanced properties. Among all the host surface-displaying microorganisms, yeast is ideally suitable for constructing whole cell-surface-displaying biocatalyst, because of the large cell size, the generally regarded as safe (GRAS) status, and the perfect post-translational processing of secreted proteins. Yeast cell-surface display system has been a promising and powerful method for development of novel and improved engineered biocatalysts. In this review, the characterization and principles of yeast cell-surface display and the applications of yeast cell-surface display in engineered whole-cell biocatalysts as well as the improvement of the enzyme efficiency are summarized and discussed.

Construction and screening of a glycosylphosphatidylinositol protein deletion library in Pichia pastoris

Background

Glycosylphosphatidylinositol (GPI)-anchored glycoproteins have diverse intrinsic functions in yeasts, and they also have different uses in vitro. In this study, the functions of potential GPI proteins in Pichia pastoris were explored by gene knockout approaches.

Results

Through an extensive knockout of GPI proteins in P. pastoris, a single-gene deletion library was constructed for 45 predicted GPI proteins. The knockout of proteins may lead to the activation of a cellular response named the ‘compensatory mechanism’, which is characterized by changes in the content and relationship between cell wall polysaccharides and surface proteins. Among the 45 deletion strains, five showed obvious methanol tolerance, four owned high content of cell wall polysaccharides, and four had a high surface hydrophobicity. Some advantages of these strains as production hosts were revealed. Furthermore, the deletion strains with high surface hydrophobicity were used as hosts to display Candida antarctica lipase B (CALB). The strain gcw22Δ/CALB-GCW61 showed excellent fermentation characteristics, including a faster growth rate and higher hydrolytic activity.

Conclusions

This GPI deletion library has some potential applications for production strains and offers a valuable resource for studying the precise functions of GPI proteins, especially their putative functions.

Novel strategy for anchorage position control of GPI-attached proteins in the yeast cell wall using different GPI-anchoring domains

The yeast cell surface provides space to display functional proteins. Heterologous proteins can be covalently anchored to the yeast cell wall by fusing them with the anchoring domain of glycosylphosphatidylinositol (GPI)-anchored cell wall proteins (GPI-CWPs). In the yeast cell-surface display system, the anchorage position of the target protein in the cell wall is an important factor that maximizes the capabilities of engineered yeast cells because the yeast cell wall consists of a 100- to 200-nm-thick microfibrillar array of glucan chains. However, knowledge is limited regarding the anchorage position of GPI-attached proteins in the yeast cell wall. Here, we report a comparative study on the effect of GPI-anchoring domain-heterologous protein fusions on yeast cell wall localization. GPI-anchoring domains derived from well-characterized GPI-CWPs, namely Sed1p and Sag1p, were used for the cell-surface display of heterologous proteins in the yeast Saccharomyces cerevisiae. Immunoelectron-microscopic analysis of enhanced green fluorescent protein (eGFP)-displaying cells revealed that the anchorage position of the GPI-attached protein in the cell wall could be controlled by changing the fused anchoring domain. eGFP fused with the Sed1-anchoring domain predominantly localized to the external surface of the cell wall, whereas the anchorage position of eGFP fused with the Sag1-anchoring domain was mainly inside the cell wall. We also demonstrate the application of the anchorage position control technique to improve the cellulolytic ability of cellulase-displaying yeast. The ethanol titer during the simultaneous saccharification and fermentation of hydrothermally-processed rice straw was improved by 30% after repositioning the exo- and endo-cellulases using Sed1- and Sag1-anchor domains. This novel anchorage position control strategy will enable the efficient utilization of the cell wall space in various fields of yeast cell-surface display technology.

Genetically Engineered Proteins to Improve Biomass Conversion: New Advances and Challenges for Tailoring Biocatalysts

Protein engineering emerged as a powerful approach to generate more robust and efficient biocatalysts for bio-based economy applications, an alternative to ecologically toxic chemistries that rely on petroleum. On the quest for environmentally friendly technologies, sustainable and low-cost resources such as lignocellulosic plant-derived biomass are being used for the production of biofuels and fine chemicals. Since most of the enzymes used in the biorefinery industry act in suboptimal conditions, modification of their catalytic properties through protein rational design and in vitro evolution techniques allows the improvement of enzymatic parameters such as specificity, activity, efficiency, secretability, and stability, leading to better yields in the production lines. This review focuses on the current application of protein engineering techniques for improving the catalytic performance of enzymes used to break down lignocellulosic polymers. We discuss the use of both classical and modern methods reported in the literature in the last five years that allowed the boosting of biocatalysts for biomass degradation.

Development of novel surface display platforms for anchoring heterologous proteins in Saccharomyces cerevisiae

Background

Cell surface display of recombinant proteins has become a powerful tool for biotechnology and biomedical applications. As a model eukaryotic microorganism, Saccharomyces cerevisiae is an ideal candidate for surface display of heterologous proteins. However, the frequently used commercial yeast surface display system, the a-agglutinin anchor system, often results in low display efficiency.

Results

We initially reconstructed the a-agglutinin system by replacing two anchor proteins with one anchor protein. By directly fusing the target protein to the N-terminus of Aga1p and inserting a flexible linker, the display efficiency almost doubled, and the activity of reporter protein α-galactosidase increased by 39%. We also developed new surface display systems. Six glycosylphosphatidylinositol (GPI) anchored cell wall proteins were selected to construct the display systems. Among them, Dan4p and Sed1p showed higher display efficiency than the a-agglutinin anchor system. Linkers were also inserted to eliminate the effects of GPI fusion on the activity of the target protein. We further used the newly developed Aga1p, Dan4p systems and Sed1p system to display exoglucanase and a relatively large protein β-glucosidase, and found that Aga1p and Dan4p were more suitable for immobilizing large proteins.

Conclusion

Our study developed novel efficient yeast surface display systems, that will be attractive tools for biotechnological and biomedical applications

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1133-x) contains supplementary material, which is available to authorized users.