Application of immobilized bovine enterokinase in repetitive fusion protein cleavage for the production of mucin 1

Bovine enterokinase is a serine protease that catalyzes the hydrolysis of peptide bonds and plays a key role in mammalian metabolism. Because of its high specificity towards the amino acid sequence (Asp)₄-Lys, enterokinase is a potential tool for the cleavage of fusion proteins, which are gaining more importance in biopharmaceutical production. A candidate for adaptive cancer immunotherapy is mucin 1, which is produced recombinantly as a fusion protein in CHO cells. Here, we present the first repetitive application of immobilized enterokinase for the cleavage of the mucin fusion protein. The immobilization enables a facile biocatalytic process due to simplified separation of the biocatalyst and the target protein. Immobilized enterokinase was applied in a maximum of 18 repetitive reactions. The enzyme utilization (total turnover number) was increased significantly 419-fold compared to unbound enzyme by both immobilization and optimization of process conditions. Slight enzyme inactivation throughout the reaction cycles was observed, but was compensated by adjusting the process time accordingly. Thus, complete fusion protein cleavage was achieved. Furthermore, we obtained isolated mucin 1 with a purity of more than 90% by applying a simple and efficient purification process. The presented results demonstrate enterokinase to be an attractive tool for fusion protein cleavage.