Different construction strategies affected on the physiology of Pichia pastoris strains highly expressed lipase by transcriptional analysis of key genes

Is heterogeneity in large-scale bioreactors a real problem in recombinant protein synthesis by Pichia pastoris?

Culture medium heterogeneity is inherent in industrial bioreactors. The loss of mixing efficiency in a large-scale bioreactor yields to the formation of concentration gradients. Consequently, cells face oscillatory culture conditions that may deeply affect their metabolism. Herein, cell response to transient perturbations, namely high methanol concentration combined with hypoxia, has been investigated using a two stirred-tank reactor compartiments (STR-STR) scale-down system and a Pichia pastoris strain expressing the gene encoding enhanced green fluorescent protein (eGFP) under the control of the alcohol oxidase 1 (AOX1) promoter. Cell residence times under transient stressing conditions were calculated based on the typical hydraulic circulation times of bioreactors of tens and hundreds cubic metres. A significant increase in methanol and oxygen uptake rates was observed as the cell residence time was increased. Stressful culture conditions impaired biomass formation and triggered cell flocculation. More importantly, both expression levels of genes under the control of pAOX1 promoter and eGFP specific fluorescence were higher in those oscillatory culture conditions, suggesting that those a priori unfavourable culture conditions in fact benefit to recombinant protein productivity. Flocculent cells were also identified as the most productive as compared to ovoid cells. KEY POINTS: • Transient hypoxia and high methanol trigger high level of recombinant protein synthesis • In Pichia pastoris, pAOX1 induction is higher in flocculent cells • Medium heterogeneity leads to morphological diversification.

Low specific growth rate and temperature in fed-batch cultures of a beta-propeller phytase producing Pichia pastoris strain under GAP promoter trigger increased KAR2 and PSA1-1 gene expression yielding enhanced extracellular productivity

Previously, we showed that the methylotrophic yeast Pichia pastoris (syn. Komagataella phaffii) could produce and secrete the beta-propeller phytase FTEII in an active form under the control of the AOX1 promoter and methanol as the inductor. In this work, we engineered P. pastoris strains to construct a constitutive P. pastoris expression system (GAP promoter) and extracellularly produce the phytase FTEII. We optimized the culture conditions to increase the extracellular volumetric phytase productivity (Q_p) and evaluated the impact of the optimization process on the physiological response of the host. Moreover, we analyzed the expression levels of the FTEII gene and endogenous genes for P. pastoris cells in cultures with the lowest and highest Q_p to understand which processes (from heterologous gene expression to protein secretion) might be responsible for the increase in Q_p. The results indicate that a low specific growth rate and temperature in the fed-batch phase increases the Q_p, which was correlated with an upregulation of the KAR2 and PSA1-1/MPG1 genes rather than increased heterologous gene transcription.

Recombinant expression of hen egg white lysozyme with the assistance of xylanase fusion partner in Pichia pastoris

Due to its bacteriolytic activity, hen egg white lysozyme (HEWL) is widely used in the feed, food, and pharmaceutical industries. However, its application is hindered by low protein expression levels in microbial expression systems. In this work, a novel fusion protein expression strategy was proposed for increasing the expression level of HEWL. First, HEWL, fused with a highly expressed fusion protein partner xylanase XynCDBFV, is expressed in Pichia pastoris. Secondly, a linker including endogenous protease cleavage sites was introduced between two fusion proteins in order to separate them directly during the secretion process. Finally, the results show that the supernatant of XynCDBFV-HEWL has a higher HEWL expression level and activity compared with HEWL only. It should be noted that the expression of HEWL reaches to about 3.5 g/L, and the activity of HEWL against Micrococcus lysodeikticus reaches to 1.50 × 10⁵ U/mL in a fed-batch fermentation, which is currently the highest level of recombinant expression of an egg white-derived lysozyme. Taken together, we acquired bioactive HEWL for large-scale recombinant production in Pichia pastoris using a novel fusion protein expression strategy, which could then be used for a variety of applications.

Recombinant Protein Production and Purification Using Eukaryotic Cell Factories

Cloning proteins enables their production and characterization for further studies. This requires inserting the gene of the studied protein to be inserted in a vector, which then will be transformed to the host cell used as "factory." Consequently, the "biomass" of host cells will be produced using bioreactors. Here we describe the production of Rhizomucor miehei lipase (RML) by cloning the corresponding genes in the yeast Pichia pastoris. This enzyme is used as a biocatalyst for biofuel production. The successfully produced recombinant proteins are then purified using ion exchange chromatography.

Improved production of recombinant Rhizomucor miehei lipase by coexpressing protein folding chaperones in Pichia pastoris, which triggered ER stress

Rhizomucor miehei lipase (RML) is a biocatalyst that widely used in laboratory and industrial. Previously, RML with a 70-amino acid propeptide (pRML) was cloned and expressed in P. pastoris. Recombinant strains with (strain containing 4-copy prml) and without ER stress (strain containing 2-copy prml) were obtained. However, the effective expression of pRML in P. pastoris by coexpressing ER-related elements in pRML-produced strain with or without ER stress has not been reported to date. In this study, an efficient way to produce functional pRML was explored in P. pastoris. The coexpression of protein folding chaperones, including PDI and ERO1, in different strains with or without ER stress, was investigated. PDI overexpression only increased pRML production in 4-copy strain from 705 U/mL to 1430 U/mL because it alleviated the protein folded stress, increased the protein concentration from 0.56  mg/mL to 0.65 mg/mL, and improved enzyme-specific activity from 1238 U/mg to 2186 U/mg. However, PDI coexpression could not improve pRML production in the 2-copy strain because it increased protein folded stress, while ERO1 coexpression in the two strains all had a negative effect on pRML expression. We also investigated the effect of the propeptide on the substrate specificity and the condition for pRML enzyme powder preparation. Results showed that the relative activity exceeded 80% when the substrates C8–C10 were detected at 35°C and pH 6, and C8–C12 at 45°C and pH 8. The optimal enzyme powder preparation pH was 7, and the maximum recovery rate for pRML was 73.19%.