Removal of cleavage slow points from affinity tags used in the IMAC purification of recombinant proteins

The complete enzymatic removal of affinity tags from tagged recombinant proteins is often required but can be challenging when slow points for cleavage exist. This study documents a general approach to remove N-terminal tags from recombinant proteins specifically designed to be efficiently captured by IMAC resins. In particular, site-directed mutagenesis procedures have been used to modify the amino acid sequence of metal binding tags useful in IMAC purifications of recombinant proteins with the objective to increase cleavage efficiency with the exopeptidase, dipeptidyl aminopeptidase 1. These tags were specifically developed for application with borderline metal ions, such as Ni(2+) or Cu(2+) ions, chelated to the immobilized ligands, 1,4,7-triazacyclononane (tacn) and its analogs. Due to the ability to control cleavage site structure and accessibility via site directed mutagenesis methods, these procedures offer considerable scope to obtain recombinant proteins with authentic native N-termini, thus avoiding any impact on structural stability, humoral and cellular immune responses, or other biological functions. Collectively, these IMAC-based methods provide a practical alternative to other procedures for the purification of recombinant proteins with tag removal. Overall, this approach is essentially operating as an integrated down-stream purification capability.