Surface display of active lipases Lip7 and Lip8 from Yarrowia Lipolytica on Saccharomyces Cerevisiae

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.

Post-Consumer Poly(ethylene terephthalate) (PET) Depolymerization by Yarrowia lipolytica: A Comparison between Hydrolysis Using Cell-Free Enzymatic Extracts and Microbial Submerged Cultivation

Several microorganisms have been reported as capable of acting on poly(ethylene terephthalate) (PET) to some extent, such as Yarrowia lipolytica, which is a yeast known to produce various hydrolases of industrial interest. The present work aims to evaluate PET depolymerization by Y. lipolytica using two different strategies. In the first one, biocatalysts were produced during solid-state fermentation (SSF-YL), extracted and subsequently used for the hydrolysis of PET and bis(2-hydroxyethyl terephthalate) (BHET), a key intermediate in PET hydrolysis. Biocatalysts were able to act on BHET, yielding terephthalic acid (TPA) (131.31 µmol L-1), and on PET, leading to a TPA concentration of 42.80 µmol L-1 after 168 h. In the second strategy, PET depolymerization was evaluated during submerged cultivations of Y. lipolytica using four different culture media, and the use of YT medium ((w/v) yeast extract 1%, tryptone 2%) yielded the highest TPA concentration after 96 h (65.40 µmol L-1). A final TPA concentration of 94.3 µmol L-1 was obtained on a scale-up in benchtop bioreactors using YT medium. The conversion obtained in bioreactors was 121% higher than in systems with SSF-YL. The results of the present work suggest a relevant role of Y. lipolytica cells in the depolymerization process.

Waste soybean frying oil for the production, extraction, and characterization of cell-wall-associated lipases from Yarrowia lipolytica

The lipolytic yeast Yarrowia lipolytica produces cell-wall-associated lipases, namely Lip7p and Lip8p, that could have interesting properties as catalyst either in free (released lipase fraction-RLF) or cell-associated (cell-bound lipase fraction-CBLF) forms. Herein, a mixture of waste soybean frying oil, yeast extract and bactopeptone was found to favor the enzyme production. Best parameters for lipase activation and release from the cell wall by means of acoustic wave treatment were defined as: 26 W/cm2 for 1 min for CBLF and 52 W/cm2 for 2 min for RLF. Optimal pH and temperature values for lipase activity together with storage conditions were similar for both the free enzyme and cell-associated one: pH 7.0; T = 37 °C; and > 70% residual activity for 60 days at 4, - 4 °C and for 15 days at 30 °C.

Engineering bioscaffolds for enzyme assembly

With the demand for green, safe, and continuous biocatalysis, bioscaffolds, compared with synthetic scaffolds, have become a desirable candidate for constructing enzyme assemblages because of their biocompatibility and regenerability. Biocompatibility makes bioscaffolds more suitable for safe and green production, especially in food processing, production of bioactive agents, and diagnosis. The regenerability can enable the engineered biocatalysts regenerate through simple self-proliferation without complex re-modification, which is attractive for continuous biocatalytic processes. In view of the unique biocompatibility and regenerability of bioscaffolds, they can be classified into non-living (polysaccharide, nucleic acid, and protein) and living (virus, bacteria, fungi, spore, and biofilm) bioscaffolds, which can fully satisfy these two unique properties, respectively. Enzymes assembled onto non-living bioscaffolds are based on single or complex components, while enzymes assembled onto living bioscaffolds are based on living bodies. In terms of their unique biocompatibility and regenerability, this review mainly covers the current advances in the research and application of non-living and living bioscaffolds with focus on engineering strategies for enzyme assembly. Finally, the future development of bioscaffolds for enzyme assembly is also discussed. Hopefully, this review will attract the interest of researchers in various fields and empower the development of biocatalysis, biomedicine, environmental remediation, therapy, and diagnosis.

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.

Cell surface display of proteins on filamentous fungi

Protein display approaches have been useful to endow the cell surface of yeasts with new catalytic activities so that they can act as enhanced whole-cell biocatalysts. Despite their biotechnological potential, protein display technologies remain poorly developed for filamentous fungi. The lignocellulolytic character of some of them coupled to the cell surface biosynthesis of valuable molecules by a single or a cascade of several displayed enzymes is an appealing prospect. Cell surface protein display consists in the co-translational fusion of a functional protein (passenger) to an anchor one, usually a cell-wall-resident protein. The abundance, spacing, and local environment of the displayed enzymes-determined by the relationship of the anchor protein with the structure and dynamics of the engineered cell wall-are factors that influence the performance of display-based biocatalysts. The development of protein display strategies in filamentous fungi could be based on the field advances in yeasts; however, the unique composition, structure, and biology of filamentous fungi cell walls require the customization of the approach to those microorganisms. In this prospective review, the cellular bases, the design principles, and the available tools to foster the development of cell surface protein display technologies in filamentous fungi are discussed.

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.

Genome mining of fungal lipid-degrading enzymes for industrial applications

Lipases are interesting enzymes, which contribute important roles in maintaining lipid homeostasis and cellular metabolisms. Using available genome data, seven lipase families of oleaginous and non-oleaginous yeast and fungi were categorized based on the similarity of their amino acid sequences and conserved structural domains. Of them, triacylglycerol lipase (patatin-domain-containing protein) and steryl ester hydrolase (abhydro_lipase-domain-containing protein) families were ubiquitous enzymes found in all species studied. The two essential lipases rendered signature characteristics of integral membrane proteins that might be targeted to lipid monolayer particles. At least one of the extracellular lipase families existed in each species of yeast and fungi. We found that the diversity of lipase families and the number of genes in individual families of oleaginous strains were greater than those identified in non-oleaginous species, which might play a role in nutrient acquisition from surrounding hydrophobic substrates and attribute to their obese phenotype. The gene/enzyme catalogue and relevant informative data of the lipases provided by this study are not only valuable toolboxes for investigation of the biological role of these lipases, but also convey potential in various industrial applications.

The contribution of Pir protein family to yeast cell surface display

Proteins with internal repeats (Pir) in the Baker's yeast are located on the cell wall and include four highly homologous members. Recently, Pir proteins have become increasingly used as anchor proteins in yeast cell surface display systems. These display systems are classified into three types: N-terminal fusion, C-terminal fusion, and inserted fusion. In addition to the GPI (glycosylphosphatidyl inositol) and the FL/FS anchor proteins, these three Pir-based systems significantly increase the choices for target proteins to be displayed. Furthermore, Pir proteins can also be used as a fusion partner for target proteins to be effectively secreted into culture medium. Here, we summarize the development and application of Pir proteins as anchor proteins.

Development of surface-engineered yeast cells displaying phytochelatin synthase and their application to cadmium biosensors by the combined use of pyrene-excimer fluorescence

The development of simple, portable, inexpensive, and rapid analytical methods for detecting and monitoring toxic heavy metals are important for the safety and security of humans and their environment. Herein, we describe the application of phytochelatin (PC) synthase, which plays a critical role in heavy metal responses in higher plants and green algae, in a novel fluorescent sensing platform for cadmium (Cd). We first created surface-engineered yeast cells on which the PC synthase from Arabidopsis (AtPCS1) was displayed with retention of enzymatic activity. The general concept for the sensor is based on the Cd level-dependent synthesis of PC2 from glutathiones by AtPCS1-displaying yeast cells, followed by simple discriminative detection of PC2 via sensing of excimer fluorescence of thiol-labeling pyrene probes. The intensity of excimer fluorescence increased in the presence of Cd up to 1.0 μM in an approximately dose-dependent manner. This novel biosensor achieved a detection limit of as low as 0.2 μM (22.5 μg/L) for Cd. Although its use may be limited by the fact that Cu and Pb can induce cross-reaction, the proposed simple biosensor holds promise as a method useful for cost-effective screening of Cd contamination in environmental and food samples. The AtPCS1-displaying yeast cells also might be attractive tools for dissection of the catalytic mechanisms of PCS.

Surface display and bioactivity of Bombyx mori acetylcholinesterase on Pichia pastoris

A Pichia pastoris (P. pastoris) cell surface display system of Bombyx mori acetylcholinesterase (BmAChE) was constructed and its bioactivity was studied. The modified Bombyx mori acetylcholinesterase gene (bmace) was fused with the anchor protein (AGα1) from Saccharomyces cerevisiae and transformed into P. pastoris strain GS115. The recombinant strain harboring the fusion gene bmace-AGα1 was induced to display BmAChE on the P. pastoris cell surface. Fluorescence microscopy and flow cytometry assays revealed that the BmAChE was successfully displayed on the cell surface of P. pastoris GS115. The enzyme activity of the displayed BmAChE was detected by the Ellman method at 787.7 U/g (wet cell weight). In addition, bioactivity of the displayed BmAChE was verified by inhibition tests conducted with eserine, and with carbamate and organophosphorus pesticides. The displayed BmAChE had an IC50 of 4.17×10(-8) M and was highly sensitive to eserine and five carbamate pesticides, as well as seven organophosphorus pesticides. Results suggest that the displayed BmAChE had good bioactivity.

New tools for exploring "old friends-microbial lipases"

Fat-splitting enzymes (lipases), due to their natural, industrial, and medical relevance, attract enough attention as fats do in our lives. Starting from the paper that we write, cheese and oil that we consume, detergent that we use to remove oil stains, biodiesel that we use as transportation fuel, to the enantiopure drugs that we use in therapeutics, all these applications are facilitated directly or indirectly by lipases. Due to their uniqueness, versatility, and dexterity, decades of research work have been carried out on microbial lipases. The hunt for novel lipases and strategies to improve them continues unabated as evidenced by new families of microbial lipases that are still being discovered mostly by metagenomic approaches. A separate database for true lipases termed LIPABASE has been created recently which provides taxonomic, structural, biochemical information about true lipases from various species. The present review attempts to summarize new approaches that are employed in various aspects of microbial lipase research, viz., screening, isolation, production, purification, improvement by protein engineering, and surface display. Finally, novel applications facilitated by microbial lipases are also presented.

Efficient cell surface display of Lip2 lipase using C-domains of glycosylphosphatidylinositol-anchored cell wall proteins of Yarrowia lipolytica

The cell surface display of enzymes is of great interest because of its simplified purification stage and the possibility for recycling in industrial processes. In this study, we have focused on the cell wall immobilization of Yarrowia lipolytica Lip2 protein--an enzyme that has a wide technological application. By genome analysis of Y. lipolytica in addition to already characterized Ylcwp1, we identified five putative open reading frames encoding glycosylphosphatidylinositol-anchored proteins. Lip2 translation fusion with the carboxyl termini of these proteins revealed that all proteins were capable of immobilizing lipase in active form on the cell surface. The highest level of cell-bound lipase activity was achieved using C-domains encoded by YlCWP1, YlCWP3 (YALI0D27214g) and YlCWP6 (YALI0F18282g) comprising 16,173 ± 1,800, 18,785 ± 1,130 and 17,700 ± 2,101 U/g dry cells, respectively. To the best of our knowledge, these results significantly exceed the highest cell-bound lipase activity previously reported for engineered Saccharomyces cerevisiae and Pichia pastoris strains. Furthermore, the lyophilized biomass retained the activity and was robust to collecting/resuspending procedures. Nevertheless, in most cases, a substantial amount of lipase activity was also found in the growth medium. Further work will be necessary to better understand the nature of this phenomenon.