Design of an improved universal signal peptide based on the α-factor mating secretion signal for enzyme production in yeast

Rational Design and Model Predictions for Optimized Elastase Production in Saccharomyces cerevisiae

Pseudomonas aeruginosa elastase is a metalloprotease with significant industrial potential but is challenging to produce due to its pathogenic origin and folding complexities. In this study, we applied rational design to engineer nonfunctional regions of elastase within Saccharomyces cerevisiae, specifically targeting propeptide and signal peptide cleavage sites, and N-glycosylation in the propeptide. This led to the development of several improved elastase variants. Integrating the yeast protein secretory model pcSecYeast with protease production characteristics, a total of 75 targets were identified and validated, comprising both model-predicted and production-feature-based targets. Notably, overexpression of POS5 enhanced protease activity to 2.43-fold that of the control, while knockout of TES1 or VPS10 further optimized production. This work demonstrates the potential of systems biology in creating yeast cell factories for protease production and highlights S. cerevisiae as a versatile host for biotechnological applications.

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.

Secretory Production of Plant Heme-Containing Globins by Recombinant Yeast via Precision Fermentation

Leghemoglobin (LegHb) is a plant-derived heme-containing globin found in the root nodules of legumes like soybean that can be used as a food additive for red color and meaty flavor as a plant-based meat alternative. However, conventional extraction methods face challenges of low yield and high costs. To address this issue, precision fermentation with recombinant microorganisms has been applied for the sustainable large-scale production of plant leghemoglobins. This study attempted the production of plant legHbs using recombinant yeast strains, Saccharomyces cerevisiae and Komagatella phaffii. The plant legHb genes were identified from the genome of legumes such as soybean, chickpea, mung bean and overexpressed in yeast via extracellular secretion by the signal peptide and inducible promoters. Subsequently, hemin as a heme provider was added to the fermentation, resulting in increased levels of plant legHbs. In S. cerevisiae, gmaLegHb expression reached up to 398.1 mg/L, while in K. phaffii, gmaLegHb showed the highest production level, reaching up to 1652.7 mg/L. The secretory production of plant legHbs was further enhanced by replacing the signal peptide in the recombinant yeast. The secreted plant legHbs were purified by His-Tag from a culture supernatant or concentrated via precipitation using ammonium sulfate. These results suggest that the production of plant legHbs is significantly influenced by hemin and signal peptide. This study successfully demonstrates the production of the various plant legHbs other than soy legHb that can be used as natural colors and flavors for plant-based meat alternatives.

An Engineered Yeast Expressing an Artificial Heavy Metal-Binding Protein Enhances the Phytoremediation of Alum Mine Soils

Alum mining leads to significant heavy metal and acid pollution within soils. Phytoremediation is a common strategy used to treat alum mine soils, but its efficiency is frequently compromised by the alum-mining-induced impairment of plant growth. To improve the strength of plants against mine pollution, this study constructed the artificial yeast strain ScHB (heavy metal-binding protein-containing Saccharomyces cerevisiae) expressing the de novo designed protein HBGFP (heavy metal-binding green fluorescence protein) and investigated its effect on the phytoremediation of alum mine soils with soil physiochemical assays and heavy metal quantification. This protein was composed of an N-terminal signal peptide, an HB (heavy metal-binding) domain, and a GFP (green fluorescence protein) domain, as well as a C-terminal glycolphosphatidylinositol-anchoring fragment. The exposure of the HBGFP on the ScHB surface increased the growth rate of the yeast cells and enhanced cadmium capture from the cadmium-containing medium. After culturing Medicago sativa in the alum mine soils for 30 days, ScHB remarkably increased the plants' average height from 17.5 cm to 27.9 cm and their biomass from 3.03 g/plant to 4.35 g/plant, as well as increasing the accumulation of antioxidant agents in the plants. Moreover, the ScHB cells strongly improved the soil quality, with an increase in the soil pH values from 5.47 to 6.21 to 6.9, and increased the levels of soil organic matter, total nitrogen, available phosphorus, and living bacteria. Furthermore, ScHB efficiently improved the plants' abilities to remove soil heavy metals, decreasing the levels of cadmium, lead, chromium, and copper by 90%, 86%, 97%, and 88%, respectively. This study developed a genetic engineering method to improve the efficiency of phytoremediation against pollution from alum mining.

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.

Optogenetic screening of MCT1 activity implicates a cluster of non-steroidal anti-inflammatory drugs (NSAIDs) as inhibitors of lactate transport

Lactate transport plays a crucial role in the metabolism, microenvironment, and survival of cancer cells. However, current drugs targeting either MCT1 or MCT4, which traditionally mediate lactate import or efflux respectively, show limited efficacy beyond in vitro models. This limitation partly arises from the existence of both isoforms in certain tumors, however existing high-affinity MCT1/4 inhibitors are years away from human testing. Therefore, we conducted an optogenetic drug screen in Saccharomyces cerevisiae on a subset of the FDA-approved drug library to identify existing scaffolds that could be repurposed as monocarboxylate transporter (MCT) inhibitors. Our findings show that several existing drug classes inhibit MCT1 activity, including non-steroidal estrogens, non-steroidal anti-inflammatory drugs (NSAIDs), and natural products (in total representing approximately 1% of the total library, 78 out of 6400), with a moderate affinity (IC50 1.8-21 μM). Given the well-tolerated nature of NSAIDs, and their known anticancer properties associated with COX inhibition, we chose to further investigate their MCT1 inhibition profile. The majority of NSAIDs in our screen cluster into a single large structural grouping. Moreover, this group is predominantly comprised of FDA-approved NSAIDs, with seven exhibiting moderate MCT1 inhibition. Since these molecules form a distinct structural cluster with known NSAID MCT4 inhibitors, such as diclofenac, ketoprofen, and indomethacin, we hypothesize that these newly identified inhibitors may also inhibit both transporters. Consequently, NSAIDs as a class, and piroxicam specifically (IC50 4.4 μM), demonstrate MCT1 inhibition at theoretically relevant human dosages, suggesting immediate potential for standalone MCT inhibition or combined anticancer therapy.

Modification of the Endoplasmic Reticulum to Enhance Ovalbumin Secretion in Saccharomyces cerevisiae

Ovalbumin (OVA) is a high-quality protein for humans. Modifying microorganisms to produce proteins offers a solution to potential food protein shortages. In this study, OVA was expressed in Saccharomyces cerevisiae. Initially, screening signal peptides led to extracellular OVA reaching 3.4 mg/L using the INU1 signal peptide. Coexpressing Kar2 and PDI increased OVA production to 5.1 mg/L. Optimizing the expression levels of regulators OPI1, INO2, and INO4 expanded the endoplasmic reticulum membrane, raising yield to 5.5 mg/L. Combining both strategies increased OVA production to 6.2 mg/L, 82% higher than control. This strategy also enhanced secretion of other proteins. Finally, fed-batch fermentation in a 3-L bioreactor significantly boosted OVA production to 116.3 mg/L. This study provides insights for the heterologous synthesis of other high-quality proteins for future food applications.

A Yeast Modular Cloning (MoClo) Toolkit Expansion for Optimization of Heterologous Protein Secretion and Surface Display in Saccharomyces cerevisiae

Saccharomyces cerevisiae is an attractive host for the expression of secreted proteins in a biotechnology context. Unfortunately, many heterologous proteins fail to enter, or efficiently progress through, the secretory pathway, resulting in poor yields. Similarly, yeast surface display has become a widely used technique in protein engineering but achieving sufficient levels of surface expression of recombinant proteins is often challenging. Signal peptides (SPs) and translational fusion partners (TFPs) can be used to direct heterologous proteins through the yeast secretory pathway, however, selection of the optimal secretion promoting sequence is largely a process of trial and error. The yeast modular cloning (MoClo) toolkit utilizes type IIS restriction enzymes to facilitate an efficient assembly of expression vectors from standardized parts. We have expanded this toolkit to enable the efficient incorporation of a panel of 16 well-characterized SPs and TFPs and five surface display anchor proteins into S. cerevisiae expression cassettes. The secretion promoting signals are validated by using five different proteins of interest. Comparison of intracellular and secreted protein levels reveals the optimal secretion promoting sequence for each individual protein. Large, protein of interest-specific variations in secretion efficiency are observed. SP sequences are also used with the five surface display anchors, and the combination of SP and anchor protein proves critical for efficient surface display. These observations highlight the value of the described panel of MoClo compatible parts to allow facile screening of SPs and TFPs and anchor proteins for optimal secretion and/or surface display of a given protein of interest in S. cerevisiae.

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.

Hypersecretory production of glucose oxidase in Pichia pastoris through combinatorial engineering of protein properties, synthesis, and secretion

Glucose oxidase (EC 1.1.3.4, GOD) is a widely used industrial enzyme. To construct a GOD-hyperproducing Pichia pastoris strain, combinatorial strategies have been applied to improve GOD activity, synthesis, and secretion. First, wild-type GOD was subjected to saturation mutagenesis to obtain an improved variant, MGOD1 (V20W/T30S), with 1.7-fold higher kcat /KM . Subsequently, efficient signal peptides were screened, and the copy number of MGOD1 was optimized to generate a high-producing strain, 8GM1, containing eight copies of AOX1 promoter-GAS1 signal peptide-MGOD1 expression cassette. Finally, the vesicle trafficking of 8GM1 was engineered to obtain the hyperproducing strain G1EeSe co-expressing the trafficking components EES and SEC. 22, and the EES gene (PAS_chr3_0685) was found to facilitate both protein secretion and production for the first time. Using these strategies, GOD secretion was enhanced 65.2-fold. In the 5-L bioreactor, conventional fed-batch fermentation without any process optimization resulted in up to 7223.0 U/mL extracellular GOD activity (3.3-fold higher than the highest level reported to date), with almost only GOD in the fermentation supernatant at a protein concentration of 30.7 g/L. Therefore, a GOD hyperproducing strain for industrial applications was developed, and this successful case can provide a valuable reference for the construction of high-producing strains for other industrial enzymes.

Engineering strategies for enhanced heterologous protein production by Saccharomyces cerevisiae

Microbial proteins are promising substitutes for animal- and plant-based proteins. S. cerevisiae, a generally recognized as safe (GRAS) microorganism, has been frequently employed to generate heterologous proteins. However, constructing a universal yeast chassis for efficient protein production is still a challenge due to the varying properties of different proteins. With progress in synthetic biology, a multitude of molecular biology tools and metabolic engineering strategies have been employed to alleviate these issues. This review first analyses the advantages of protein production by S. cerevisiae. The most recent advances in improving heterologous protein yield are summarized and discussed in terms of protein hyperexpression systems, protein secretion engineering, glycosylation pathway engineering and systems metabolic engineering. Furthermore, the prospects for efficient and sustainable heterologous protein production by S. cerevisiae are also provided.

Fungal Laccases: Fundamentals, Engineering and Classification Update

Multicopper oxidases (MCOs) share a common catalytic mechanism of activation by oxygen and cupredoxin-like folding, along with some common structural determinants. Laccases constitute the largest group of MCOs, with fungal laccases having the greatest biotechnological applicability due to their superior ability to oxidize a wide range of aromatic compounds and lignin, which is enhanced in the presence of redox mediators. The adaptation of these versatile enzymes to specific application processes can be achieved through the directed evolution of the recombinant enzymes. On the other hand, their substrate versatility and the low sequence homology among laccases make their exact classification difficult. Many of the ever-increasing amounts of MCO entries from fungal genomes are automatically (and often wrongly) annotated as laccases. In a recent comparative genomic study of 52 basidiomycete fungi, MCO classification was revised based on their phylogeny. The enzymes clustered according to common structural motifs and theoretical activities, revealing three novel groups of laccase-like enzymes. This review provides an overview of the structure, catalytic activity, and oxidative mechanism of fungal laccases and how their biotechnological potential as biocatalysts in industry can be greatly enhanced by protein engineering. Finally, recent information on newly identified MCOs with laccase-like activity is included.

Improving therapeutic protein secretion in the probiotic yeast Saccharomyces boulardii using a multifactorial engineering approach

The probiotic yeast Saccharomyces boulardii (Sb) is a promising chassis to deliver therapeutic proteins to the gut due to Sb's innate therapeutic properties, resistance to phage and antibiotics, and high protein secretion capacity. To maintain therapeutic efficacy in the context of challenges such as washout, low rates of diffusion, weak target binding, and/or high rates of proteolysis, it is desirable to engineer Sb strains with enhanced levels of protein secretion. In this work, we explored genetic modifications in both cis- (i.e. to the expression cassette of the secreted protein) and trans- (i.e. to the Sb genome) that enhance Sb's ability to secrete proteins, taking a Clostridioides difficile Toxin A neutralizing peptide (NPA) as our model therapeutic. First, by modulating the copy number of the NPA expression cassette, we found NPA concentrations in the supernatant could be varied by sixfold (76-458 mg/L) in microbioreactor fermentations. In the context of high NPA copy number, we found a previously-developed collection of native and synthetic secretion signals could further tune NPA secretion between 121 and 463 mg/L. Then, guided by prior knowledge of S. cerevisiae's secretion mechanisms, we generated a library of homozygous single gene deletion strains, the most productive of which achieved 2297 mg/L secretory production of NPA. We then expanded on this library by performing combinatorial gene deletions, supplemented by proteomics experiments. We ultimately constructed a quadruple protease-deficient Sb strain that produces 5045 mg/L secretory NPA, an improvement of > tenfold over wild-type Sb. Overall, this work systematically explores a broad collection of engineering strategies to improve protein secretion in Sb and highlights the ability of proteomics to highlight under-explored mediators of this process. In doing so, we created a set of probiotic strains that are capable of delivering a wide range of protein titers and therefore furthers the ability of Sb to deliver therapeutics to the gut and other settings to which it is adapted.

Alternative secretory signal sequences for recombinant protein production in Pichia pastoris

Extracellular protein production is primarily preferred to facilitate the downstream processes in recombinant protein production. Secretion of recombinant proteins is mediated by the processing of signal peptides in their N-terminal portion by the secretory mechanism of host expression systems. These molecular elements involved in secretion are functionally interchangeable between different species and secretion sequence screening is one of the widely used approaches to improve extracellular protein production. In this study, α-mating and protein internal repeats (PIR) secretion sequences isolated from different yeasts (Kluyveromyces lactis, Kluyveromyces marxianus and Hansenula polymorpha) were tested in Pichia pastoris for the production of two different proteins (α-amylase and xylanase) and compared with the well-known secretory signals, S. cerevisiae α-mating factor (Sc-MF) and P. pastoris protein internal repeats PIR (PpPIR). The results obtained showed the potential of signal sequences tested. Among the tested peptides, the highest yields were achieved with H. polymorpha protein internal repeats (HpPIR) and K. lactis α-mating factor (Kl-MF) for xylanase and K. marxianus protein internal repeats (KmPIR) and K. lactis α-mating factor (Kl-MF) for amylase. In further studies, these sequences can be evaluated as alternatives in the production of different proteins in P. pastoris and in the production of recombinant proteins in different expression systems.

Molecular Modification of Kex2 P1' Site Enhances Expression and Druggability of Fungal Defensin

Pichia pastoris is the widely used expression system for producing recombinant secretory proteins. It is known that Kex2 protease plays a vital role in the process of protein secretion, in which the P1' site affects its cleavage efficiency. To enhance the expression level of fungal defensin-derived peptide NZ2114, this work attempts to optimize the P1' site of Kex2 by replacing it with 20 amino acids in turn. The results showed that when the amino acid of the P1' site was changed to Phe (F), the yield of target peptide significantly increased from 2.39 g/L to 4.81 g/L. Additionally, the novel peptide F-NZ2114 (short for FNZ) showed strong antimicrobial activity against Gram-positive (G⁺) bacteria, especially for Staphylococcus aureus and Streptococcus agalactiae (MIC: 4-8 μg/mL). The FNZ was very stable and retained high activity in various conditions; in addition, a low cytotoxicity and no hemolysis were observed even at a high concentration of 128 μg/mL, and a longer postantibiotic effect was reached. The above results indicate that this engineering strategy provided a feasible optimization scheme for enhancing the expression level and druggability of this antimicrobial peptide from fungal defensin and other similar targets by this updated recombinant yeast.

Comprehensive Analysis of Signal Peptides in Saccharomyces cerevisiae Reveals Features for Efficient Secretion

Signal peptides (SPs) are N-terminus sequences on the nascent polypeptide for protein export or localization delivery, which are essential for maintaining cell function. SPs are also employed as a key element for industrial production of secreted recombinant proteins. Yet, detailed information and rules about SPs and their cellular interactions are still not well understood. Here, systematic bioinformatics analysis and secretion capacity measurement of genome-wide SPs from the model organism Saccharomyces cerevisiae is performed. Several key features of SPs, including region properties, consensus motifs, evolutionary relationships, codon bias, e.g., are successfully revealed. Diverse cell metabolism can be trigged by using different SPs for heterologous protein secretion. Influences on SPs with different properties by chaperones can cause different secretory efficiencies. Protein secretion by the SP NCW2 in SEC72 deletion strain is 10 times than the control. These findings provide insights into the properties and functions of SPs and contribute to both fundamental research and industrial application.

Expression of a Salt-Tolerant Pseudolysin in Yeast for Efficient Protein Hydrolysis under High-Salt Conditions

Protease biocatalysis in a high-salt environment is very attractive for applications in the detergent industry, the production of diagnostic kits, and traditional food fermentation. However, high-salt conditions can reduce protease activity or even inactivate enzymes. Herein, in order to explore new protease sources, we expressed a salt-tolerant pseudolysin of Pseudomonas aeruginosa SWJSS3 isolated from deep-sea mud in Saccharomyces cerevisiae. After optimizing the concentration of ion cofactors in yeast peptone dextrose (YPD) medium, the proteolytic activity in the supernatant was 2.41 times more than that in the control group when supplemented with 5 mM CaCl₂ and 0.4 mM ZnCl₂. The extracellular proteolytic activity of pseudolysin reached 258.95 U/mL with optimized expression cassettes. In addition, the S. cerevisiae expression system increased the salt tolerance of pseudolysin to sodium chloride (NaCl)and sodium dodecyl sulfate (SDS) and the recombinant pseudolysin retained 15.19% activity when stored in 3 M NaCl for 7 days. The recombinant pseudolysin was able to efficiently degrade the β-conglycinin from low-denatured soy protein isolates and glycinin from high-denatured soy protein isolates under high temperatures (60 °C) and high-salt (3 M NaCl) conditions. Our study provides a salt-tolerant recombinant protease with promising applications in protein hydrolysis under high-salt conditions.

Tailor-made alkaliphilic and thermostable fungal laccases for industrial wood processing

BACKGROUND

During the kraft process to obtain cellulosic pulp from wood, most of the lignin is removed by high-temperature alkaline cooking, released in the black liquors and usually incinerated for energy. However, kraft lignins are a valuable source of phenolic compounds that can be valorized in new bio-based products. The aim of this work is to develop laccases capable of working under the extreme conditions of high temperature and pH, typical of the industrial conversion of wood into kraft pulp and fibreboard, in order to provide extremophilic biocatalysts for depolymerising kraft lignin, and enzyme-assisted technologies for kraft pulp and fibreboard production.

RESULTS

Through systematic enzyme engineering, combining enzyme-directed evolution and rational design, we changed the optimal pH of the laccase for oxidation of lignin phenols from acidic to basic, enhanced the catalytic activity at alkaline pH and increased the thermal tolerance of the enzyme by accumulating up to eight mutations in the protein sequence. The extremophilic laccase variants show maximum activity at 70 °C and oxidize kraft lignin at pH 10. Their integration into industrial-type processes saves energy and chemicals. As a pre-bleaching stage, the enzymes promote kraft pulp bleachability and significantly reduce the need for chlorine dioxide compared to the industrial sequence. Their application in wood chips during fibreboard production, facilitates the defibering stage, with less energy required.

CONCLUSIONS

A set of new alkaliphilic and thermophilic fungal laccases has been developed to operate under the extreme conditions of high temperature and pH typical of industrial wood conversion processes. For the first time basidiomycete laccases of high-redox potential show activity on lignin-derived phenols and polymeric lignin at pH 10. Considering the extreme conditions of current industrial processes for kraft pulp and fibreboard production, the new tailor-made laccases constitute a step forward towards turning kraft pulp mills into biorefineries. Their use as biocatalysts in the wood conversion sector is expected to support the development of more environmentally sound and efficient processes, and more sustainable products.

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.

Eisosome disruption by noncoding RNA deletion increases protein secretion in yeast

Noncoding RNAs (ncRNAs) regulate many aspects of gene expression. We investigated how ncRNAs affected protein secretion in yeast by large-scale screening for improved endogenous invertase secretion in ncRNA deletion strains with deletion of stable unannotated transcripts (SUTs), cryptic unstable transcripts (CUTs), tRNAs, or snRNAs. We identified three candidate ncRNAs, SUT418, SUT390, and SUT125, that improved endogenous invertase secretion when deleted. As SUTs can affect expression of nearby genes, we quantified adjacent gene transcription and found that the PIL1 gene was down-regulated in the SUT125 deletion strain. Pil1 is a core component of eisosomes, nonmobile invaginations found throughout the plasma membrane. PIL1 knockout alone, or in combination with eisosome components LSP1 or SUR7, resulted in further increased secretion of invertase. Secretion of heterologous GFP was also increased upon PIL1 deletion, but this increase was signal sequence dependent. To reveal the potential for increased biopharmaceutical production, secretion of monoclonal antibody Pexelizumab scFv peptide was increased by PIL1 deletion. Global analysis of secreted proteins revealed that approximately 20% of secreted proteins, especially serine-enriched secreted proteins, including invertase, were increased upon eisosome disruption. Eisosomes are enriched with APC transporters and sphingolipids, which are essential components for secretory vesicle formation and protein sorting. Sphingolipid and serine biosynthesis pathways were up-regulated upon PIL1 deletion. We propose that increased secretion of endogenous and heterologous proteins upon PIL1 deletion resulted from sphingolipid redistribution in the plasma membrane and up-regulated sphingolipid biosynthesis. Overall, a new pathway to improve protein secretion in yeast via eisosome disruption has been identified.

Avoiding entry into intracellular protein degradation pathways by signal mutations increases protein secretion in Pichia pastoris

In our previous study, we serendipitously discovered that protein secretion in the methylotrophic yeast Pichia pastoris is enhanced by a mutation (V50A) in the mating factor alpha (MFα) prepro‐leader signal derived from Saccharomyces cerevisiae. In the present study, we investigated 20 single‐amino‐acid substitutions, including V50A, located within the MFα signal peptide, indicating that V50A and several single mutations alone provided significant increase in production of the secreted proteins. In addition to hydrophobicity index analysis, both an unfolded protein response (UPR) biosensor analysis and a microscopic observation showed a clear difference on the levels of UPR induction and mis‐sorting of secretory protein into vacuoles among the wild‐type and mutated MFα signal peptides. This work demonstrates the importance of avoiding entry of secretory proteins into the intracellular protein degradation pathways, an observation that is expected to contribute to the engineering of strains with increased production of recombinant secreted proteins.

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.