Enhancing xylanase expression of Komagataella phaffii induced by formate through Mit1 co-expression

PEX3 gene knockout influences recombinant xylanase expression by Komagataella phaffii

Komagataella phaffii is a methylotrophic yeast harboring a tightly regulated alcohol oxidase promoter (P AOX1 ), which is now widely used for recombinant protein production. During P AOX1 expression phase by methanol induction, a methanol metabolism organelle peroxisome enlarged and occupied 80 % of K. phaffii cell through peroxins functions of matrix protein import and organelle division. Using a K. phaffii expressing xylanase in this study, each of all 23 PEX genes of K. phaffii, encoding peroxin, was knockout to influence the peroxisome size, leading to changes of K. phaffii physiological status and recombinant xylanase expression. It was observed that PEX3 knockout reduced peroxisome size by 54.3 %, increased xylanase expression by 29 %, decreased apoptosis ratio by 70.6 %. Transcriptome analysis revealed that PEX3 gene knockout decreased 18 other PEX genes of all three steps of peroxisome propagation, biogenesis, matrix protein import, and peroxisome fission. PEX3 gene knockout influenced expression of ribosomal subunit-related and protein transportation significantly based on gene function annotation and enrichment analysis. Additionally, Therefore, PEX3 gene knockout promoted xylanase folding correctly via Sec63 complex, and PDI1 significantly. In a summary, PEX3 gene knockout provided a novel strategy to enhance recombinant xylanase by K. phaffii.

Formate from THF-C1 metabolism induces the AOX1 promoter in formate dehydrogenase-deficient Komagataella phaffii

In Komagataella phaffii (Pichia pastoris), formate is a recognized alternative inducer to methanol for expression systems based on the AOX1 promoter (pAOX1). By disrupting the formate dehydrogenase encoding FDH1 gene, we converted such a system into a self-induced one, as adding any inducer in the culture medium is no longer requested for pAOX1 induction. In cells, formate is generated from serine through the THF-C1 metabolism, and it cannot be converted into carbon dioxide in a FdhKO strain. Under non-repressive culture conditions, such as on sorbitol, the intracellular formate generated from the THF-C1 metabolism is sufficient to induce pAOX1 and initiate protein synthesis. This was evidenced for two model proteins, namely intracellular eGFP and secreted CalB lipase from C. antarctica. Similar protein productivities were obtained for a FdhKO strain on sorbitol and a non-disrupted strain on sorbitol-methanol. Considering a K. Phaffii FdhKO strain as a workhorse for recombinant protein synthesis paves the way for the further development of methanol-free processes in K. phaffii.

Selection of DNA aptamers for the aptamer-assisted magnetic capture of the purified xylanase from Aspergillus niger

Xylanases are a group of enzymes that catalyze the hydrolysis of xylan. Xylanases have wide industrial applications, and they can produced by various organisms. In this study, we aimed to develop aptamers for the capture of xylanase produced by a wild-type Aspergillus niger strain. Xylanase was produced by Aspergillus niger in a 5-liter stirred-tank bioreactor and then purified by column chromatography. Magnetic bead-based SELEX (Systematic Evolution of Ligands by Exponential Enrichment) was performed to select DNA aptamers specific to the purified xylanase. After nine rounds of selection, next-generation sequencing (NGS) analysis was performed. Four aptamers, namely AXYL-1, AXYL-2, AXYL-3, and AXYL-4, were identified for further characterization. The binding properties of the selected aptamers were characterized by fluorescence quenching (FQ) analysis and an enzyme-linked aptamer assay (ELAA). The Kd values were found to be in the low μM range. Then, each aptamer was immobilized on streptavidin-coated magnetic particles, and the recovery ratio of xylanase was determined. Although AXYL-1 wasn't effective, AXYL-2, AXYL-3, and AXYL-4 were proven to capture the xylanase. The maximum recovery rate of xylanase was found to be approximately 54 %.

Expression level of SOR1 is a bottleneck for efficient sorbitol utilization by yeast Komagataella kurtzmanii

The yeast strain Komagataella kurtzmanii VKPM Y-727 shows a significant defect in sorbitol utilization compared to closely related yeast K. phaffii (including strains formerly identified as Pichia pastoris). Our aim was to investigate the factors that determine the phenotype of the wild-type strain and to obtain a K. kurtzmanii strain with an improved ability to utilize sorbitol. We sequenced and annotated the genome of K. kurtzmanii VKPM Y-727 and compared it with that of K. phaffii GS115. Five K. phaffii GS115 genes that might be involved in sorbitol metabolism were selected and transferred into K. kurtzmanii Y-727. The transfer of the modified SOR1 gene resulted in an increased growth rate of K. kurtzmanii in sorbitol, despite the fact that Y-727 already contains its own SOR1 gene without any apparent mutations. The enzymes encoded by the SOR1 genes were analyzed in vitro and found to have similar properties. Differences in promoter activity were assessed using lacZ as a reporter gene, and the PSDH727  (promoter of SOR1 (SDH727) from K. kurtzmanii Y-727) promoter was shown to be 1.5-2.0 times weaker than PSDH115  (promoter of SOR1 (SDH115) from K. phaffii GS115). Moreover, both promoters were less active in K. kurtzmanii than in K. phaffii when evaluated in cells grown in synthetic complete media with glucose or sorbitol. Thus, SOR1 gene expression was identified as a bottleneck in sorbitol metabolism in K. kurtzmanii. Also, the positive effect of additional modified SOR1 gene copies was observed in both yeasts, as K. kurtzmanii and K. phaffii could grow on synthetic complete media with sorbitol three times faster than the original K. phaffii GS115 strain.

An inducible Komagataella phaffii system for protein expression using sorbitol dehydrogenase promoter

OBJECTIVES

The aim of the present work was to develop a methanol-independent Komagataella phaffii (K. phaffii) strain using a non-methanol promoter.

RESULTS

In this study, the food grade enzyme xylanase from Aspergillus niger ATCC 1015 was used as the reporter protein, a recombinant K. phaffii containing a cascade gene circus was designed and constructed using sorbitol as inducer. Sorbitol induced P_SDH leading to MIT1 expression firstly, and heterologous protein xylanase expression finally. This system showed 1.7 fold of xylanase activity at the condition of single copy number of extra MIT1, and 2.1 fold of xylanase activity at condition of multi-copy extra MIT1 gene.

CONCLUSIONS

This sorbitol-induced expression system of K. phaffii avoided toxic and explosive methanol. It was a novel cascade gene expression and a food safety system.

P AOX1 expression in mixed-substrate continuous cultures of Komagataella phaffii (Pichia pastoris) is completely determined by methanol consumption regardless of the secondary carbon source

The expression of recombinant proteins by the AOX1 promoter of Komagataella phaffii is typically induced by adding methanol to the cultivation medium. Since growth on methanol imposes a high oxygen demand, the medium is often supplemented with an additional secondary carbon source which serves to reduce the consumption of methanol, and hence, oxygen. Early research recommended the use of glycerol as the secondary carbon source, but more recent studies recommend the use of sorbitol because glycerol represses P AOX1 expression. To assess the validity of this recommendation, we measured the steady state concentrations of biomass, residual methanol, and LacZ expressed from P AOX1 over a wide range of dilution rates (0.02-0.20 h-1) in continuous cultures of the Mut+ strain fed with methanol + glycerol (repressing) and methanol + sorbitol (non-repressing). We find that under these conditions, the specific P AOX1 expression rate (measured as either specific LacZ productivity or specific AOX productivity) is completely determined by the specific methanol consumption rate regardless of the type (repressing/non-repressing) of the secondary carbon source. In both cultures, the specific P AOX1 expression rate is proportional to the specific methanol consumption rate, provided that the latter is below 0.15 g/(gdw-h); beyond this threshold consumption rate, the specific P AOX1 expression rate of both cultures saturates to the same value. Analysis of the data in the literature shows that the same phenomenon also occurs in continuous cultures of Escherichia coli fed with mixtures of lactose plus repressing/non-repressing carbon sources. The specific P lac expression rate is completely determined by the specific lactose consumption rate, regardless of the type of secondary carbon source, glycerol or glucose.