Activation of the Unfolded Protein Response via Co-expression of the HAC1i Gene Enhances Expression of Recombinant Elastase in Pichia pastoris

The effects of activation of the unfolded protein response (UPR) via co-expression of the HAC1(i) gene on the production of the recombinant Pseudomonas aeruginosa elastase (rPAE) in Pichia pastoris GS115 were evaluated in this study. The results showed that expression of the HAC1(i) gene significantly increased the level of Kar2p (a hallmark of UPR activation) in P. pastoris GS115, demonstrating activation of the UPR. This gene did not affect the growth of yeast in the buffered glycerol-complex medium but stimulated its growth in the buffered methanol-complex medium. Co-expression of the HAC1(i) gene enhanced the expression level of the heterogeneously N-glycosylated forms of rPAE, as the caseinolytic activity in the supernatant of the various glycoforms of rPAE expressed in P. pastoris GS115/HAC1 was increased 1.8-3.9-fold compared to that in the control strain P. pastoris GS115, respectively. The stimulating effects of co-expression of the gene on rPAE production were observed when 0.5, 1.0, and 2.0% methanol were added every 24 h, as the caseinolytic activity of supernatants of P. pastoris GS115/HAC1 expressing wild-type of rPAE was increased 3.3-, 1.9-, and 1.7-fold at the corresponding methanol concentration. Further, activation of UPR via co-expression of the HAC1(i) gene enhanced rPAE secretion in P. pastoris at 20, 24, and 28 degrees C, as the caseinolytic activity of supernatants of P. pastoris GS115/HAC1 expressing wild-type rPAE was increased 2.3-, 2.1-, and 2.8-fold over the tested temperatures.