Construction of a novel system for cell surface display of heterologous proteins on Pichia pastoris

Safety profile of intravenous administration of live Pichia pastoris cells in mice

Pichia pastoris has been widely used to produce antigenic proteins aimed to integrate subunit vaccines. Moreover, increasing interest in large-scale vaccine production at the lowest cost is rapidly focusing in the development of yeast surface display (YSD) systems for delivery of antigens. In this scenario, the safety of live yeast administration must be warranted, however such information is very scarce. Here we assess the intravenous administration (i.v.) of live P. pastoris cells in order to trace dissemination in BALB/c mice and to evaluate the immune response raised against the yeast compared to the well-defined pathogen Candida albicans. Our results demonstrate dissemination of P. pastoris to the heart, kidney, and spleen, but it is quickly eliminated during the first 48 hours post-infection (hpi), with persistence in the liver along with mild mononuclear and polymorphonuclear (PMN) infiltrate, which was resolved at 144 hpi. In vivo delayed-type hyper-sensitivity test (DTH) or in vitro antigenic stimulation of mice splenocytes demonstrate that transient infection of P. pastoris did not induce a cell-mediated immune response nor increase the level of circulating IgG or IgM. These results demonstrate the innocuous profile of P. pastoris and support its use as a safe delivery system for vaccine development.

Oral administration of Saccharomyces cerevisiae displaying VP28-VP24 confers protection against white spot syndrome virus in shrimp

White spot syndrome virus (WSSV) is the major pathogen that leads to severe mortalities in cultured shrimp worldwide. The envelope proteins VP28 and VP24 of WSSV are considered potential vaccine candidate antigens. In this study, we utilized a Saccharomyces cerevisiae (S. cerevisiae) surface display system to demonstrate the feasibility of this platform for developing a vaccine candidate against WSSV. EBY100/pYD1-VP28-VP24 was generated, and the fusion protein VP28-VP24 was present on the surface of S. cerevisiae. Penaeus vannamei (P. vannamei) was used as an animal model. Oral administration of EBY100/pYD1-VP28-VP24 could induce significant activities of immune-related enzymes such as superoxide dismutase (SOD) and phenoloxidase (PO). Importantly, WSSV challenge indicated that oral administration of EBY100/pYD1-VP28-VP24 could confer 100% protection with a corresponding decrease in the viral load. The collective results strongly highlight the potential of a S. cerevisiae-based oral vaccine as an efficient control strategy for combating WSSV infection in shrimp aquaculture.

Surface Display—An Alternative to Classic Enzyme Immobilization

Enzyme immobilization to solid matrices often presents a challenge due to protein conformation sensitivity, desired enzyme purity, and requirements for the particular carrier properties and immobilization technique. Surface display of enzymes at the cell walls of microorganisms presents an alternative that has been the focus of many research groups worldwide in different fields, such as biotechnology, energetics, pharmacology, medicine, and food technology. The range of systems by which a heterologous protein can be displayed at the cell surface allows the appropriate one to be found for almost every case. However, the efficiency of display systems is still quite low. The most frequently used yeast for the surface display of proteins is Saccharomyces cerevisiae. However, apart from its many advantages, Saccharomyces cerevisiae has some disadvantages, such as low robustness in industrial applications, hyperglycosylation of some heterologous proteins, and relatively low efficiency of surface display. Thus, in the recent years the display systems for alternative yeast hosts with better performances including Pichia pastoris, Hansenula polymorpha, Blastobotrys adeninivorans, Yarrowia lipolytica, Kluyveromyces marxianus, and others have been developed. Different strategies of surface display aimed to increase the amount of displayed protein, including new anchoring systems and new yeast hosts are reviewed in this paper.

Yeast arming systems: pros and cons of different protein anchors and other elements required for display

Yeast display is a powerful strategy that consists in exposing peptides or proteins of interest on the cell surface of this microorganism. Ever since initial experiments with this methodology were carried out, its scope has extended and many applications have been successfully developed in different science and technology fields. Several yeast display systems have been designed, which all involve introducting into yeast cells the gene fusions that contain the coding regions of a signal peptide, an anchor protein, to properly attach the target to the cell surface, and the protein of interest to be exposed, all of which are controlled by a strong promoter. In this work, we report the description of such elements for the alternative systems introduced by focusing particularly on anchor proteins. The comparisons made between them are included whenever possible, and the main advantages and inconveniences of each one are discussed. Despite the huge number of publications on yeast surface display and the revisions published to date, this topic has not yet been widely considered. Finally, given the growing interest in developing systems for non-Saccharomyces yeasts, the main strategies reported for some are also summarized.

Cell-Surface Displayed Expression of Trehalose Synthase from Pseudomonas putida ATCC 47054 in Pichia Pastoris Using Pir1p as an Anchor Protein

Yeast cell-surface display technologies have been widely applied in the fields of food, medicine, and feed enzyme production, including lipase, α-amylase, and endoglucanase. In this study, a treS gene was fused with the yeast cell-surface anchor protein gene Pir1p by overlap PCR, the Pir1p-treS fusion gene was ligated into pPICZαA and pGAPZαA and transformed into P. pastoris GS115 to obtain recombinant yeast strains that displays trehalose synthase(TreS) on its cell surface as an efficient and recyclable whole-cell biocatalyst. Firstly, the enhanced green fluorescence protein gene (egfp) was used as the reporter protein to fusion the Pir1p gene and treS gene to construct the recombinant plasmids containing treS-egfg-Pir1p fusion gene, and electrotransformed into P. pastoris GS115 to analyze the surface display characteristics of fusion gene by Western blot, fluorescence microscopy and flow cytometry. The analysis shown that the treS-egfg-Pir1p fusion protein can be successfully displayed on the surface of yeast cell, and the expression level increased with the extension of fermentation time. These results implied that the Pir1p-treS fusion gene can be well displayed on the cell surface. Secondly, in order to obtain surface active cells with high enzyme activity, the enzymatic properties of TreS displayed on the cell surface was analyzed, and the fermentation process of recombinant P. patoris GS115 containing pPICZαA-Pir1p-treS and pGAPZαA-Pir1p-treS was studied respectively. The cell surface display TreS was stable over a broad range of temperatures (10-45°C) and pH (6.0-8.5). The activity of TreS displayed on cell surface respectively reached 1,108 Ug^-1 under P_AOX1 control for 150 h, and 1,109 Ug^-1 under P_GAP control for 75h in a 5 L fermenter, respectively. Lastly, the cell-surface displayed TreS was used to product trehalose using high maltose syrup as substrate at pH 8.0 and 15°C. The surface display TreS cells can be recycled for three times and the weight conversion rate of trehalose was more than 60%. This paper revealed that the TreS can display on the P. pastoris cell surface and still had a higher catalytic activity after recycled three times, which was suitable for industrial application, especially the preparation of pharmaceutical grade trehalose products.

Establishment of cell surface engineering and its development

Cell surface display of proteins/peptides has been established based on mechanisms of localizing proteins to the cell surface. In contrast to conventional intracellular and extracellular (secretion) expression systems, this method, generally called an arming technology, is particularly effective when using yeasts as a host, because the control of protein folding that is often required for the preparation of proteins can be natural. This technology can be employed for basic and applied research purposes. In this review, I describe various strategies for the construction of engineered yeasts and provide an outline of the diverse applications of this technology to industrial processes such as the production of biofuels and chemicals, as well as bioremediation and health-related processes. Furthermore, this technology is suitable for novel protein engineering and directed evolution through high-throughput screening, because proteins/peptides displayed on the cell surface can be directly analyzed using intact cells without concentration and purification. Functional proteins/peptides with improved or novel functions can be created using this beneficial, powerful, and promising technique.

Displaying Lipase B from Candida antarctica in Pichia pastoris Using the Yeast Surface Display Approach: Prospection of a New Anchor and Characterization of the Whole Cell Biocatalyst

Yeast Surface Display (YSD) is a strategy to anchor proteins on the yeast cell wall which has been employed to increase enzyme stability thus decreasing production costs. Lipase B from Candida antarctica (LipB) is one of the most studied enzymes in the context of industrial biotechnology. This study aimed to assess the biochemical features of this important biocatalyst when immobilized on the cell surface of the methylotrophic yeast Pichia pastoris using the YSD approach. For that purpose, two anchors were tested. The first (Flo9) was identified after a prospection of the P. pastoris genome being related to the family of flocculins similar to Flo1 but significantly smaller. The second is the Protein with Internal Repeats (Pir1) from P. pastoris. An immunolocalization assay showed that both anchor proteins were able to display the reporter protein EGFP in the yeast outer cell wall. LipB was expressed in P. pastoris fused either to Flo9 (FLOLIPB) or Pir1 (PIRLIPB). Both constructions showed hydrolytic activity towards tributyrin (>100 U/mg_dcw and >80 U/mg_dcw, respectively), optimal hydrolytic activity around 45°C and pH 7.0, higher thermostability at 45°C and stability in organic solvents when compared to a free lipase.

Yeast Surface Display of Two Proteins Previously Shown to Be Protective Against White Spot Syndrome Virus (WSSV) in Shrimp

Cell surface display using the yeasts Saccharomyces cerevisiae and Pichia pastoris has been extensively developed for application in bioindustrial processes. Due to the rigid structure of their cell walls, a number of proteins have been successfully displayed on their cell surfaces. It was previously reported that the viral binding protein Rab7 from the giant tiger shrimp Penaeus monodon (PmRab7) and its binding partner envelope protein VP28 of white spot syndrome virus (WSSV) could independently protect shrimp against WSSV infection. Thus, we aimed to display these two proteins independently on the cell surfaces of 2 yeast clones with the ultimate goal of using a mixture of the two clones as an orally deliverable, antiviral agent to protect shrimp against WSSV infection. PmRab7 and VP28 were modified by N-terminal tagging to the C-terminal half of S. cerevisiae α-agglutinin. DNA fragments, harboring fused-gene expression cassettes under control of an alcohol oxidase I (AOX1) promoter were constructed and used to transform the yeast cells. Immunofluorescence microscopy with antibodies specific to both proteins demonstrated that mutated PmRab7 (mPmRab7) and partial VP28 (pVP28) were localized on the cell surfaces of the respective clones, and fluorescence intensity for each was significantly higher than that of control cells by flow cytometry. Enzyme-linked immunosorbant assay (ELISA) using cells displaying mPmRab7 or pVP28 revealed that the binding of specific antibodies for each was dose-dependent, and could be saturated. In addition, the binding of mPmRab7-expressing cells with free VP28, and vice versa was dose dependent. Binding between the two surface-expressed proteins was confirmed by an assay showing agglutination between cells expressing complementary mPmRab7 and pVP28. In summary, our genetically engineered P. pastoris can display biologically active mPmRab7 and pVP28 and is now ready for evaluation of efficacy in protecting shrimp against WSSV by oral administration.

Citrobacter amalonaticus phytase on the cell surface of Pichia pastoris exhibits high pH stability as a promising potential feed supplement

Phytase expressed and anchored on the cell surface of Pichia pastoris avoids the expensive and time-consuming steps of protein purification and separation. Furthermore, yeast cells with anchored phytase can be used as a whole-cell biocatalyst. In this study, the phytase gene of Citrobacter amalonaticus was fused with the Pichia pastoris glycosylphosphatidylinositol (GPI)-anchored glycoprotein homologue GCW61. Phytase exposed on the cell surface exhibits a high activity of 6413.5 U/g, with an optimal temperature of 60°C. In contrast to secreted phytase, which has an optimal pH of 5.0, phytase presented on the cell surface is characterized by an optimal pH of 3.0. Moreover, our data demonstrate that phytase anchored on the cell surface exhibits higher pH stability than its secreted counterpart. Interestingly, our in vitro digestion experiments demonstrate that phytase attached to the cell surface is a more efficient enzyme than secreted phytase.

Development of new tolerant strains to hydrophilic and hydrophobic organic solvents by the yeast surface display methodology

Yeast surface display is a research methodology based on anchoring functional proteins and peptides onto the surface of the cells of this eukaryotic organism. Its development has resulted in the construction of a good number of new whole-cell biocatalysts with diverse applications in biotechnology, pharmacy, and medicine. In this work, we describe the design of new yeast strains in which several proteins and peptides have been introduced at the N-terminal position of protein agglutinin Aga2p. In all cases, proteins were correctly expressed and displayed on the cell surface according to the western blot, fluorescence microscopy, and fluorescence-activated cell sorting (FACS) analyses. The introduction of a glycosylable, Ser/Thr-rich protein (S1) resulted in improved resistance to ethanol, nonane, and dimethyl sulfoxide (DMSO) stress. The protein with a very high hydrophobic content (S2d) proved to confer tolerance to acetonitrile, ethanol, nonane, salt, and sodium dodecyl sulfate (SDS). The introduction of five leucine residues at the N-terminal position of S1 and S2 resulted in similar or increased resistance to the above-mentioned stress conditions. The adverse effects described in a previous work, when these residues were introduced into the N-terminus of Aga2p, with no other protein acting as a spacer, were not observed. Indeed, these strains grew better in the presence of hydrophilic solvents such as acetonitrile and ethanol. The new strains reported in this work have biotechnological potentiality given their behavior under adverse conditions of interest for biocatalytic and industrial processes.

Arming Technology in Yeast-Novel Strategy for Whole-cell Biocatalyst and Protein Engineering

Cell surface display of proteins/peptides, in contrast to the conventional intracellular expression, has many attractive features. This arming technology is especially effective when yeasts are used as a host, because eukaryotic modifications that are often required for functional use can be added to the surface-displayed proteins/peptides. A part of various cell wall or plasma membrane proteins can be genetically fused to the proteins/peptides of interest to be displayed. This technology, leading to the generation of so-called "arming technology", can be employed for basic and applied research purposes. In this article, we describe various strategies for the construction of arming yeasts, and outline the diverse applications of this technology to industrial processes such as biofuel and chemical productions, pollutant removal, and health-related processes, including oral vaccines. In addition, arming technology is suitable for protein engineering and directed evolution through high-throughput screening that is made possible by the feature that proteins/peptides displayed on cell surface can be directly analyzed using intact cells without concentration and purification. Actually, novel proteins/peptides with improved or developed functions have been created, and development of diagnostic/therapeutic antibodies are likely to benefit from this powerful approach.

Display of active beta-glucosidase on the surface of Schizosaccharomyces pombe cells using novel anchor proteins

Here, we demonstrate display of beta-glucosidase (BGL) on the surface of Schizosaccharomyces pombe cells using novel anchor proteins. A total of four candidate anchor proteins (SPBC21D10.06c, SPBC947.04, SPBC19C7.05, and SPBC359.04c) were selected from among almost all of S. pombe membrane proteins. The C-terminus of each anchor protein was genetically fused to the N-terminus of BGL, and the fusion protein was expressed using S. pombe as a host. The highest cell surface-associated BGL activity (107 U/10(5) cells was achieved with SPBC359.04c serving as the anchor, followed by SPBC947.04 (44 U/10(5) cells) and SPBC21D10.06c (38 U/10(5) cells). S. pombe displaying BGL with SPBC359.04c as an anchor showed the highest growth on 2 % cellobiose (10.7 × 10(7) cells/mL after 41 h of cultivation from an initial density of 0.1 × 10(7) cells/mL). Additionally, culturing BGL-displaying S. pombe in medium containing cellobiose as the sole carbon source did not affect protein expression, and ethanol fermentation from cellobiose was successfully demonstrated using BGL-displaying S. pombe. This is the first report describing a cell surface display system for the functionalization of S. pombe.

Development of a novel rDNA based plasmid for enhanced cell surface display on Yarrowia lipolytica

In this study, a novel rDNA based plasmid was developed for display of heterologous proteins on the cell surface of Yarrowia lipolytica using the C-terminal end of the glycosylphosphatidylinositol (GPI) anchored Y. lipolytica cell wall protein 1 (YlCWP1). mCherry was used as a model protein to assess the efficiency of the constructed plasmid. Y. lipolytica transformants harbouring the expression cassettes showed a purple colour phenotype on selective YNB-casamino plates as compared to control cells indicating that mCherry was displayed on the cells. Expression of mCherry on cells of Y. lipolytica was confirmed by both fluorescent microscopy and flow cytometry. Furthermore, SDS-PAGE analysis and matrix-assisted laser desorption/ionization (MALDI)-time-of (TOF)-mass spectrometry (MS) peptide mass fingerprinting (PMF) confirmed that the protein cleaved from the yeast cells using enterokinase was mCherry. Efficient cleavage of mCherry reported in this work offers an alternative purification method for displayed heterologous proteins on Y. lipolytica cells using the plasmid constructed in this study. The developed displaying system offers great potential for industrial production and purification of heterologous proteins at low cost.

A novel fragment of antigen binding (Fab) surface display platform using glycoengineered Pichia pastoris

A fragment of antigen binding (Fab) surface display system was developed using a glycoengineered Pichia pastoris host strain genetically modified to secrete glycoproteins with mammalian mannose-type Man(5)GlcNAc(2) N-linked glycans. The surface display method described here takes advantage of a pair of coiled-coil peptides as the linker while using the Saccharomyces cerevisiae Sed1p GPI-anchored cell surface protein as an anchoring domain. Several Fabs were successfully displayed on the cell surface using this system and the expression level of the displayed Fabs was correlated to that of secreted Fabs from the same glycoengineered host in the absence of the cell wall anchor. Strains displaying different model Fabs were mixed and, through cell sorting, the strain displaying more expressed Fab molecule or the strain displaying the Fab with higher affinity for an antigen was effectively enriched by FACS. This novel yeast surface display system provides a general platform for the display of Fab libraries for affinity and/or expression maturation using glycoengineered Pichia.

Surface display of human lactoferrin using a glycosylphosphatidylinositol-anchored protein of Saccharomyces cerevisiae in Pichia pastoris

A cell surface display system was developed in Pichia pastoris using the gene TIP1, encoding the glycosylphosphatidylinositol (GPI)-anchored protein of Saccharomyces cerevisiae (ScTIP). Human lactoferrin cDNA (hLf) was fused to a full-length TIP1 DNA (ScTIP ( 630 )) or a short-TIP1 fragment (ScTIP ( 120 )) encoding the 40 C-terminal amino acids of ScTIP. Both hLf-ScTIP fusion genes were expressed in P. pastoris SMD 1168. The fused protein was detected by western blotting after extraction of the lysed recombinant cells with Triton X-100, urea, and Triton X-100 plus urea, suggesting that the hLf is associated with the membrane. The localization of surface-displayed hLf was confirmed by immunofluorescence confocal microscopy and flow cytometric analysis using FITC-labeled anti-hLf antibody, suggesting that hLf was successfully located at the surface of P. pastoris. The intact recombinant cells and cell lysates showed antibacterial activity against target microorganisms, meaning that the expressed hLf was biologically active. The results indicated that the ScTIP anchoring motif is useful for cell surface display of foreign proteins in P. pastoris.

Cell surface display of highly pathogenic avian influenza virus hemagglutinin on the surface of Pichia pastoris cells using alpha-agglutinin for production of oral vaccines

Yeast is an ideal organism to express viral antigens because yeast glycosylate proteins more similarly to mammals than bacteria. Expression of proteins in yeast is relatively fast and inexpensive. In addition to the convenience of production, for purposes of vaccination, yeast has been shown to have natural adjuvant activity making the expressed proteins more immunogenic when administered along with yeast cell wall components. Development of genetic systems to display foreign proteins on the surface of yeast via fusion to glycosylphosphatidylinositol-anchored (GPI) proteins has further simplified the purification of recombinant proteins by not requiring harsh treatments for cellular lysis or protein purification. We have expressed the hemagglutinin protein from a highly pathogenic avian influenza (HPAI) virus [A/Egret/HK/757.2/02], subtype H5N1, on the surface of the yeast strain Pichia pastoris, as an anchored C-terminal fusion with the Saccharomyces cerevisiae GPI-anchored cell wall protein, alpha-agglutinin. Surface expression of the hemagglutinin fusion protein was demonstrated by immunofluorescence microscopy. Functionally, the fusion protein retained hemagglutinin agglutinating activity, and oral vaccination with the yeast resulted in production of virus neutralizing antibodies. This study represents the first steps in the generation of a yeast-based vaccine for protection against highly pathogenic strains of avian influenza.

Display of Candida antarctica lipase B on Pichia pastoris and its application to flavor ester synthesis

Two alternative cell-surface display systems were developed in Pichia pastoris using the alpha-agglutinin and Flo1p (FS) anchor systems, respectively. Both the anchor cell wall proteins were obtained originally from Saccharomyces cerevisiae. Candida antarctica lipase B (CALB) was displayed functionally on the cell surface of P. pastoris using the anchor proteins alpha-agglutinin and FS. The activity of CALB displayed on P. pastoris was tenfold higher than that of S. cerevisiae. The hydrolytic and synthetic activities of CALB fused with alpha-agglutinin and FS anchored on P. pastoris were investigated. The hydrolytic activities of both lipases displayed on yeast cells surface were more than 200 U/g dry cell after 120 h of culture (200 and 270 U/g dry cell, respectively). However, the synthetic activity of CALB fused with alpha-agglutinin on P. pastoris was threefold higher than that of the FS fusion protein when applied to the synthesis of ethyl caproate. Similarly, the CALB displayed on P. pastoris using alpha-agglutinin had a higher catalytic efficiency with respect to the synthesis of other short-chain flavor esters than that displayed using the FS anchor. Interestingly, for some short-chain esters, the synthetic activity of displaying CALB fused with alpha-agglutinin on P. pastoris was even higher than that of the commercial CALB Novozyme 435.

Isolation of antigen-binding camelid heavy chain antibody fragments (nanobodies) from an immune library displayed on the surface of Pichia pastoris

Yeast surface display is an efficient tool for isolating and engineering antibody fragments, both scFv and Fab. We describe the use of protein display on Pichia pastoris for the rapid selection of camelid antibodies composed only of heavy chains (nanobodies) from a library derived from a llama immunized with Green Fluorescent Protein. The library of nanobody-coding sequences was fused to the C-terminal part of the Saccharomyces cerevisiae alpha-agglutinin gene (SAG1) and expressed in glycoengineered P. pastoris. A high efficiency transformation protocol yielded a library of 5x10(7) clones. About 80% of the clones strongly expressed the nanobody fusion. Nanobody-displaying clones were rapidly enriched by fluorescence activated cell sorting (FACS), and GFP-specific nanobody-displaying clones were isolated and equilibrium dissociation constants (K(d)) determined. This technology for displaying protein libraries on P. pastoris enables the isolation and engineering of antibody-derived molecules in a robust eukaryotic expression host.

Pichia surface display: display of proteins on the surface of glycoengineered Pichia pastoris strains

Expression of proteins on the surface of yeasts has a wide range of applications in biotechnology, such as directed evolution of proteins for increased affinity and thermal stability, screening of antibody libraries, epitope mapping, and use as whole-cell biocatalysts. However, hyperglycosylation can interfere with overall protein accessibility on the surface. Therefore, the less elaborate hyperglycosylation in wild type Pichia pastoris and the availability of glycoengineered strains make this yeast an excellent alternative for surface display of glycoproteins. Here, we report the implementation of the well-established a-agglutinin-based yeast surface display technology in P. pastoris. Four heterologous proteins were expressed on the surface of a wild type and a glycoengineered strain. Surface display levels were monitored by Western blot, immunofluorescence microscopy, and FACS analysis. The availability of glycoengineered strains makes P. pastoris an excellent alternative for surface display of glycoproteins and paves the way for new applications.