Fusion proteins of organophosphorus hydrolase and pHluorin for a whole-cell biosensor for organophosphorus pesticide measurement

Fusion proteins composed of an organophosphorus hydrolase (OPH) and pHluorin, a pH-sensitive green fluorescent protein variant, were constructed as whole-cell biosensors to measure organophosphorus pesticides. pHluorin was used to detect the pH changes because of the hydrolase of paraoxon by OPH. To examine the order of fusion of OPH and pHluorin, pHluorin-OPH and OPH-pHluorin fusion proteins were constructed. In addition, a peptide linker consisting of 15 amino acid was inserted between pHluorin and OPH to reduce steric hindrance. OPH and pHluorin activities were evaluated in cells expressing the four fusion proteins. The both activities of pHluorin-OPH and pHluorin-linker-OPH were higher than that of OPH-pHluorin and OPH-linker-pHluorin. Effects of the peptide linker on the activities were slight. Therefore, pHluorin-OPH and pHluorin-linker-OPH were found to be suitable for organophosphorus pesticide measurements. Using cells expressing pHluorin-linker-OPH, 0.5 μg/mL of paraoxon could be measured.

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

Yeast displaying enzymes on the cell surface are used for developing whole-cell biocatalysts. High enzyme activity on the cell surface is required in certain applications such as direct ethanol production from lignocellulosic materials. However, the cell surface enzyme activity is limited by several factors, one of which is the protein amount of the yeast cell wall. In this study, we attempted to improve the incorporation capacity of a displayed heterologous enzyme by disrupting a native cell-wall protein. β-Glucosidase (BGL1) from Aspergillus aculeatus was fused with Saccharomyces cerevisiae Sed1 and displayed on the cell surface of S. cerevisiae BY4741 strain and its SED1 disruptant. Sed1 is one of the most abundant stationary phase yeast cell wall protein. A time course analysis revealed that BGL1 activity of the control strain reached saturation after 48 h of cultivation. In contrast, the BGL1 activity of the SED1 disruptant increased until 72 h of cultivation and was 22% higher than that of the control strain. We also performed relative quantification of cell wall proteins of these strains by nanoscale ultra pressure liquid chromatography electrospray ionization quadrupole time-of-flight tandem mass spectrometry (nano-UPLC-MS^E). The amount of the cell wall-associated BGL1 per unit dry cell-weight of the SED1 disruptant was 19% higher than that of the control strain. These results suggested that the incorporation capacity of the cell wall for BGL1 was increased by disruption of SED1. Disruption of SED1 would be a promising approach for improving display efficiency of heterologous protein fused with Sed1.

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.

Secretory expression of organophosphorus hydrolase OPHC2 in Yarrowia lipolytica Polg

In the present study, recombinant organophosphorus hydrolase OPHC2 was successfully produced by Yarrowia lipolytica and purified. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot analyses showed a major polypeptide band of 36 kDa. The purified enzyme was optimally active at 65°C and pH 8.5 and also displayed good thermal and pH stability using methyl parathion (O,O-dimethyl-O-4-p-nitrophenyl phosphorothioate) as a substrate. Moreover, as Y. lipolytica is a non-pathogenic, generally regarded as safe (GRAS) yeast, the cell culture supernatant can be used directly on vegetables and fruits that are contaminated by organophosphorus pesticides.

Temporal and spatial properties of a yeast multi-cellular amplification system based on signal molecule diffusion

We report on the spatial and temporal signaling properties of a yeast pheromone-based cell communication and amplifier system. It utilizes the Saccharomyces cerevisiae mating response pathway and relies on diffusion of the pheromone α-factor as key signaling molecule between two cell types. One cell type represents the α-factor secreting sensor part and the other the reporter part emitting fluorescence upon activation. Although multi-cellular signaling systems promise higher specificity and modularity, the complex interaction of the cells makes prediction of sensor performance difficult. To test the maximum distance and response time between sensor and reporter cells, the two cell types were spatially separated in defined compartments of agarose hydrogel (5 x 5 mm) and reconnected by diffusion of the yeast pheromone. Different ratios of sensor to reporter cells were tested to evaluate the minimum amount of sensor cells required for signal transduction. Even the smallest ratio, one α-factor-secreting cell to twenty reporter cells, generated a distinct fluorescence signal. When using a 1:1 ratio, the secreted pheromone induced fluorescence in a distance of up to four millimeters after six hours. We conclude from both our experimental results and a mathematical diffusion model that in our approach: (1) the maximum dimension of separated compartments should not exceed five millimeters in gradient direction; and (2) the time-limiting step is not diffusion of the signaling molecule but production of the reporter protein.

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.

Cell surface engineering of yeast for applications in white biotechnology

Cell surface engineering is a promising strategy for the molecular breeding of whole-cell biocatalysts. By using this strategy, yeasts can be constructed by the cell surface display of functional proteins; these yeasts are referred to as arming yeasts. Because reactions using arming yeasts as whole-cell biocatalysts occur on the cell surface, materials that cannot enter the cell can be used as reaction substrates. Numerous arming yeasts have therefore been constructed for a wide range of uses such as biofuel production, synthesis of valuable chemicals, adsorption or degradation of environmental pollutants, recovery of rare metal ions, and biosensors. Here, we review the science of yeast cell surface modification as well as current applications and future opportunities.