1-Cyanocyclohexaneacetic acid (1-CHAA) is a critical intermediate for the synthesis of the antiepileptic agent gabapentin. Previously, our group has established a novel manufacturing route for 1-CHAA through bioconversion catalyzed by an Escherichia coli (E. coli) nitrilase whole cell catalyst. However, the nitrilase expressed in E. coli has several drawbacks such as a low level of reusability, which hampered its industrial application. Herein, we investigated the potential of using the methylotrophic yeast Pichia pastoris (P. pastoris) for producing the nitrilase whole cell catalyst. To achieve strains with high catalytic activities, we investigated the effects of the promoter choice, expressing cassette copy number, and co-expression of chaperone on the production of nitrilase. Our results demonstrated that the strain harboring the multicopy integrations of nitrilase gene under the control of the alcohol oxidase 1 (AOX1) promoter and co-expressing of ER oxidoreductin 1 (ERO1) exhibited an 18-fold enhancement in the nitrilase activity compared with the strain containing a single integration of nitrilase gene under the control of glyceraldehyde-3-phosphate (GAP) dehydrogenase promoter. This optimized P. pastoris strain, compared with the E. coli nitrilase whole cell catalyst, shows greatly improved levels of reusability and thermostability while has a similar high-substrate tolerance.
Keywords: Bioconversion; Chaperone; Gene dosage; Nitrilase; Pichia pastoris; Whole cell catalyst.