Disulfide bond engineering of AppA phytase for increased thermostability requires co-expression of protein disulfide isomerase in Pichia pastoris

• Main Authors: Blinco, J.-A (Author), Chen, X. (Author), Luangthongkam, P. (Author), Luna-Flores, C.H (Author), Mahler, S. (Author), Navone, L. (Author), Speight, R. (Author), Vogl, T. (Author), von Hellens, J. (Author)
• Format: Article
• Language: English
• Published: BioMed Central Ltd 2021
• Subjects: biochemistry; Chaperone; Cobalt compounds; coliform bacterium; Covalent bonds; Dietary supplements; Disulfide bond; Enzymatic properties; enzyme activity; Enzyme development; Enzymes; Escherichia coli; Folding; gene expression; incubation; Industrial processs; Parallel development; pH; phosphatase; Phytase; Pichia pastoris; Production bottlenecks; protein; Protein disulfide isomerases; Protein engineering; Recombinant proteins; Stability; Statistical differences; Sulfur compounds; temperature anomaly; Thermostability; yeast; Yeast
• Online Access: View Fulltext in Publisher

 Background: Phytases are widely used commercially as dietary supplements for swine and poultry to increase the digestibility of phytic acid. Enzyme development has focused on increasing thermostability to withstand the high temperatures during industrial steam pelleting. Increasing thermostability often reduces activity at gut temperatures and there remains a demand for improved phyases for a growing market. Results: In this work, we present a thermostable variant of the E. coli AppA phytase, ApV1, that contains an extra non-consecutive disulfide bond. Detailed biochemical characterisation of ApV1 showed similar activity to the wild type, with no statistical differences in kcat and KM for phytic acid or in the pH and temperature activity optima. Yet, it retained approximately 50% activity after incubations for 20 min at 65, 75 and 85 °C compared to almost full inactivation of the wild-type enzyme. Production of ApV1 in Pichia pastoris (Komagataella phaffi) was much lower than the wild-type enzyme due to the presence of the extra non-consecutive disulfide bond. Production bottlenecks were explored using bidirectional promoters for co-expression of folding chaperones. Co-expression of protein disulfide bond isomerase (Pdi) increased production of ApV1 by ~ 12-fold compared to expression without this folding catalyst and restored yields to similar levels seen with the wild-type enzyme. Conclusions: Overall, the results show that protein engineering for enhanced enzymatic properties like thermostability may result in folding complexity and decreased production in microbial systems. Hence parallel development of improved production strains is imperative to achieve the desirable levels of recombinant protein for industrial processes. © 2021, The Author(s).