The bud tip is the cellular hot spot of protein secretion in yeasts

Efficient Bioproduction of Human Milk Alpha-Lactalbumin in Komagataella phaffii

Alpha-lactalbumin (α-LA; the most abundant whey protein in human milk) contributes to infant development, providing bioactive peptides and essential amino acids. Here, Komagataella phaffii (K. phaffii) was selected as the production host. We found that the K. phaffii host X33 was suitable for expressing the target protein, yielding 5.2 mg·L^-1 α-LA. Thereafter, several secretory signal peptides were applied to obtain a higher titer of α-LA. The strain with α-factor secretory signal peptide secreted the highest extracellular titer. Additionally, promoters AOX1, GAP, and GAP(m) were compared and applied. The strain with the promoter AOX1 produced the highest extracellular titer. In addition, coexpressing human protein disulfide isomerase A3 (hPDIA3) increased the titer by 27%. Human α-LA production by the strain X33-pPICZαA-hLALBA-hPDIA3 reached 56.3 mg·L^-1 in a 3 L bioreactor. This is the first report of successful secretory human α-LA expression in K. phaffii and lays foundations for the simulation of human milk for infant formulas and further development of bioengineered milk.

Targeted Deletion of Los1 Homologue Affects the Production of a Recombinant Model Protein in Pichia pastoris

Background:

The methylotrophic yeast Pichia pastoris is an appealing production host for a variety of recombinant proteins, including biologics. In this sense, various genetic- and non-genetic-based techniques have been implemented to improve the production efficiency of this expression platform. Los1 (loss of supression) encodes a non-essential nuclear tRNA exporter in Saccharomyces cerevisiae, which its deletion extends RLS. Herein, a los1-deficient strain of P. pastoris was generated and characterized.

Methods:

A gene disruption cassette was prepared and transformed into an anti-CD22-expressing strain of P. pastoris. A δ los1 mutant was isolated and confirmed. The drug sensitivity of the mutant was also assessed. The growth pattern and the level of anti-CD22 ScFv expression were compared between the parent and mutant strains.

Results:

The los1 homologue was found to be a non-essential gene in P. pastoris. Furthermore, the susceptibility of los1 deletion strain to protein synthesis inhibitors was altered. This strain showed an approximately 1.85-fold increase in the extracellular level of anti-CD22 scFv (p < 0.05). The maximum concentrations of total proteins secreted by δ los1 and parent strains were 125 mg/L and 68 mg/L, respectively.

Conclusion:

The presented data suggest that the targeted disruption of los1 homologue in P. pastoris can result in a higher expression level of our target protein. Findings of this study may improve the current strategies used in optimizing the productivity of recombinant P. pastoris strains.

Engineering of the unfolded protein response pathway in Pichia pastoris: enhancing production of secreted recombinant proteins

Folding and processing of proteins in the endoplasmic reticulum (ER) are major impediments in the production and secretion of proteins from Pichia pastoris (Komagataella sp.). Overexpression of recombinant genes can overwhelm the innate secretory machinery of the P. pastoris cell, and incorrectly folded proteins may accumulate inside the ER. To restore proper protein folding, the cell naturally triggers an unfolded protein response (UPR) pathway, which upregulates the expression of genes coding for chaperones and other folding-assisting proteins (e.g., Kar2p, Pdi1, Ero1p) via the transcription activator Hac1p. Unfolded/misfolded proteins that cannot be repaired are degraded via the ER-associated degradation (ERAD) pathway, which decreases productivity. Co-expression of selected UPR genes, along with the recombinant gene of interest, is a common approach to enhance the production of properly folded, secreted proteins. Such an approach, however, is not always successful and sometimes, protein productivity decreases because of an unbalanced UPR. This review summarizes successful chaperone co-expression strategies in P. pastoris that are specifically related to overproduction of foreign proteins and the UPR. In addition, it illustrates possible negative effects on the cell's physiology and productivity resulting from genetic engineering of the UPR pathway. We have focused on Pichia's potential for commercial production of valuable proteins and we aim to optimize molecular designs so that production strains can be tailored to suit a specific heterologous product. KEY POINTS: • Chaperones co-expressed with recombinant genes affect productivity in P. pastoris. • Enhanced UPR may impair strain physiology and promote protein degradation. • Gene copy number of the target gene and the chaperone determine the secretion rate.

Characterization of methanol utilization negative Pichia pastoris for secreted protein production: New cultivation strategies for current and future applications

The methanol utilization (Mut) phenotype in the yeast Pichia pastoris (syn. Komagataella spp.) is defined by the deletion of the genes AOX1 and AOX2. The Mut- phenotype cannot grow on methanol as a single carbon source. We assessed the Mut- phenotype for secreted recombinant protein production. The methanol inducible AOX1 promoter (PAOX1 ) was active in the Mut- phenotype and showed adequate eGFP fluorescence levels and protein yields (YP/X ) in small-scale screenings. Different bioreactor cultivation scenarios with methanol excess concentrations were tested using PAOX1 HSA and PAOX1 vHH expression constructs. Scenario B comprising a glucose-methanol phase and a 72-hr-long methanol only phase was the best performing, producing 531 mg/L HSA and 1631 mg/L vHH. 61% of the HSA was produced in the methanol only phase where no biomass growth was observed, representing a special case of growth independent production. By using the Mut- phenotype, the oxygen demand, heat output, and specific methanol uptake (qmethanol ) in the methanol phase were reduced by more than 80% compared with the MutS phenotype. The highlighted improved process parameters coupled with growth independent protein production are overlooked benefits of the Mut- strain for current and future applications in the field of recombinant protein production.

Filamentous fungi-like secretory pathway strayed in a yeast system: peculiarities of Yarrowia lipolytica secretory pathway underlying its extraordinary performance

Microbial production of secretory proteins constitutes one of the key branches of current industrial biotechnology, earning billion dollar (USD) revenues each year. That industrial branch strongly relies on fluent operation of the secretory machinery within a microbial cell. The secretory machinery, directing the nascent polypeptide to its final destination, constitutes a highly complex system located across the eukaryotic cell. Numerous molecular identities of diverse structure and function not only build the advanced network assisting folding, maturation and secretion of polypeptides but also serve as sensors and effectors of quality control points. All these events must be harmoniously orchestrated to enable fluent processing of the protein traffic. Availability of these elements is considered to be the limiting factor determining capacity of protein traffic, which is of crucial importance upon biotechnological production of secretory proteins. The main purpose of this work is to review and discuss findings concerning secretory machinery operating in a non-conventional yeast species, Yarrowia lipolytica, and to highlight peculiarities of this system prompting its use as the production host. The reviewed literature supports the thesis that secretory machinery in Y. lipolytica is characterized by significantly higher complexity than a canonical yeast protein secretion pathway, making it more similar to filamentous fungi-like systems in this regard.