CRISPR/Cas9-Mediated Construction of a YPS Gene-Deficient Komagataella phaffii Strain for Enhanced Expression of BIAP...

Multiple isoforms of bovine intestinal alkaline phosphatase (BIAP) have been identified, among which type Ⅱ (BIAP Ⅱ) exhibits the highest specific activity. While Komagataella phaffii has been successfully employed for the secretory expression of recombinant BIAP Ⅱ, substantial proteolytic degradation during the secretion and expression processes has been observed, leading to reduced protein yield and challenging purification procedures. Our investigation demonstrates that the proteolytic cleavage of BIAP Ⅱ is predominantly mediated by secretory pathway proteases, particularly the aspartic protease yapsin (Yps), with Yps1 playing a crucial role. Genetic disruption of the YPS1 gene resulted in a remarkable 2.5-fold increase in BIAP Ⅱ production yield compared to the parental strain, accompanied by significantly reduced proteolytic degradation. Through detailed analysis, we have identified the Yps1 cleavage site within the BIAP Ⅱ peptide chain, located between Lys₁₃₇ and Lys₁₃₈. To further minimize BIAP Ⅱ proteolysis, we developed a YPS multigene-deficient engineered strain using CRISPR/Cas9-mediated triple gene editing technology. Additionally, we have established a novel dual-color quantitative PCR (DC-qPCR) method that enables rapid and precise determination of target gene dosage, thereby enhancing screening efficiency while reducing experimental errors associated with repeated sample processing. The strategies and methodologies developed in this study may serve as a valuable reference for optimizing the expression of various secretory heterologous proteins in Komagataella phaffii.