Internal ribosome entry site mediates protein synthesis in yeast Pichia pastoris

Variable eIF4E-binding sites and their synergistic effect on cap-independent translation in a novel IRES of wheat yellow mosaic virus RNA2 isolates

Some viral proteins are translated cap-independently via the internal ribosome entry site (IRES), which maintains conservative characteristic among different isolates of the same virus species. However, IRES activity showed a 7-fold variance in RNA2 of wheat yellow mosaic virus (WYMV) HC and LYJN isolates in this study. Based on RNA structure probing and mutagenesis assay, the loosened middle stem of H1 and the hepta-nucleotide top loop of H2 in the LYJN isolate synergistically ensured higher IRES activity than that in the HC isolate. In addition, the conserved top loop of H1 ensured basic IRES activity in HC and LYJN isolates. WYMV RNA2 5'-UTR specifically interacted with the wheat eIF4E, accomplished by the top loop of H1 in the HC isolate or the top loop of H1 and H2 in the LYJN isolate. The high IRES activity of the WYMV RNA2 LYJN isolate was regulated by two eIF4E-binding sites, which showed a synergistic effect mediated by the proximity of the H1 and H2 top loops owing to the flexibility of the middle stem in H1. This report presents a novel evolution pattern of IRES, which altered the number of eIF4E-binding sites to regulate IRES activity.

Co-expressing GroEL-GroES, Ssa1-Sis1 and Bip-PDI chaperones for enhanced intracellular production and partial-wall breaking improved stability of porcine growth hormone

Porcine growth hormone (pGH) is a class of peptide hormones secreted from the pituitary gland, which can significantly improve growth and feed utilization of pigs. However, it is unstable and volatile in vitro. It needs to be encapsulated in liposomes when feeding livestock, whose high cost greatly limits its application in pig industry. Therefore we attempted to express pGH as intracellular soluble protein in Pichia pastoris and feed these yeasts with partial wall-breaking for swine, which could release directly pGH in intestine tract in case of being degraded in intestinal tract with low cost. In order to improve the intracellular soluble expression of pGH protein in Pichia pastoris and stability in vitro, we optimized the pGH gene, and screened molecular chaperones from E. coli and Pichia pastoris respectively for co-expressing with pGH. In addition, we had also explored conditions of mechanical crushing and fermentation. The results showed that the expression of intracellular soluble pGH protein was significantly increased after gene optimized and co-expressed with Ssa1-Sis1 chaperone from Pichia pastoris. Meanwhile, the optimal conditions of partial wall-breaking and fermentation of Pichia pastoris were confirmed, the data showed that the intracellular expression of the optimized pGH protein co-expressed with Ssa1-Sis1 could reach 340 mg/L with optimal conditions of partial wall-breaking and fermentation. Animal experiments verified that the optimized pGH protein co-expression with Ssa1-Sis1 had the best promoting effects on the growth of piglets. Our study demonstrated that Ssa1-Sis1 could enhance the intracellular soluble expression of pGH protein in Pichia pastoris and that partial wall-breaking of yeast could prevent pGH from degradation in vitro, release targetedly in the intestine and play its biological function effectively. Our study could provide a new idea to cut the cost effectively, establishing a theoretical basis for the clinic application of unstable substances in vitro.

Screening for functional IRESes using α-complementation system of β-galactosidase in Pichia pastoris

BACKGROUND

Pichia pastoris is becoming a promising chassis cell for metabolic engineering and synthetic biology after its whole genome and transcriptome sequenced. However, the current systems for multigene co-expression in P. pastoris are not efficient. The internal ribosome entry site (IRES) has an ability to recruit the ribosome to initiate protein synthesis by cap-independent translation manner. This study seeks to screen IRES sequences that are functional in P. pastoris, which will allow P. pastoris to express multiple proteins in a single mRNA and increase its efficacy as a platform for metabolic engineering and synthetic biology.

RESULTS

In order to efficiently screen the IRES sequences, we first set out to create a screening system using LacZ gene. Due to the cryptic transcription of the LacZ gene, we established the α-complementation system of β-galactosidase in P. pastoris with the optimum length of the α-complementing peptide at ~ 92 amino acids. The optimal α-complementing peptide was then used as the second reporter to screen IRESes in the engineered GS115 expressing the corresponding ω-peptide. A total of 34 reported IRESes were screened. After ruling out all false positive or negative IRESes, only seven IRESes were functional in P. pastoris, which were from TEV, PVY, RhPV, TRV, KSHV, crTMV viruses and the 5'-UTR of the YAP1 gene of S. cerevisiae.

CONCLUSIONS

We showed here that α-complementation also works in P. pastoris and it can be used in a variety of in vivo studies. The functional IRESes screened in this study can be used to introduce multiple genes into P. pastoris via a prokaryotic-like polycistronic manner, which provided new efficient tools for metabolic engineering and synthetic biology researches in P. pastoris.

A systematic analysis of the expression of the anti-HIV VRC01 antibody in Pichia pastoris through signal peptide optimization

Pichia pastoris (Komagataella phaffi) has been used for recombinant protein production for over 30 years with over 5000 proteins reported to date. However, yields of antibody are generally low. We have evaluated the effect of secretion signal peptides on the production of a broadly neutralizing antibody (VRC01) to increase yield. Eleven different signal peptides, including the murine IgG1 signal peptide, were combinatorially evaluated for their effect on antibody titer. Strains using different combinations of signal peptides were identified that secreted approximately 2–7 fold higher levels of VRC01 than the previous best secretor, with the highest yield of 6.50 mg L⁻¹ in shake flask expression. Interestingly it was determined that the highest yields were achieved when the murine IgG1 signal peptide was fused to the light chain, with several different signal peptides leading to high yield when fused to the heavy chain. Finally, we have evaluated the effect of using a 2A signal peptide to create a bicistronic vector in the attempt to reduce burden and increase transformation efficiency, but found it to give reduced yields compared to using two independent vectors.

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Production of VRC01 antibody in Pichia pastoris was increased 2–7 fold.

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Using the murine IgG1 signal peptide on the light chain results in higher yields.

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The use of bicistronic vectors did not increase the yield of VRC01.

Effect of cooperation of chaperones and gene dosage on the expression of porcine PGLYRP-1 in Pichia pastoris

Mammalian peptidoglycan recognition proteins (PGLYRPs) are highly conserved pattern-recognition molecules of the innate immune system with considerable bactericidal activity, which manifest their potential values for the application to food and pharmaceutical industry. However, the effective expression of porcine PGLYRP-1 in Pichia pastoris has not been reported so far. In this study, expression in P. pastoris was explored as an efficient way to produce functional porcine PGLYRP-1. Cooperation of chaperones co-expression and gene dosage (including protein disulfide isomerase (PDI)/binding protein (BiP) and pglyrp-1) were used to enhance functional expression of antimicrobial protein in P. pastoris. Overexpression of PDI was certainly able to increase secretion level of PGLYRP-1 protein because the increase in secreted PGLYRP-1 secretion was correlated with the copy numbers of PDI in high copy pglyrp-1 clones. However, co-expression of BiP was proved to be detrimental to PGLYRP-1 secretion. In addition, we also found that excessive expression of PDI and/or BiP could decrease the mRNA expression of pglyrp-1 gene. This showed that PDI and BiP as the target genes of unfolded protein response (UPR) might regulate the transcription of the target protein. These data demonstrated for the first time that the combination of chaperones and gene dosages could improve the yield of PGLYRP-1, which could facilitate the application to food and pharmaceutical industry.