A novel expression vector for production of epitope-tagged recombinant Fab fragments in bacteria

Labeling of recombinant Fab molecules is an important yet cumbersome and time-consuming procedure that is needed in many immunological experimental designs. This work describes the development of a novel expression vector fusing to the carboxyterminal of the Fab heavy chain fragments a tag peptide (FLAG) that is consistently recognized by a mouse monoclonal antibody. The presence of the FLAG peptide does not alter the binding characteristics of the unmodified Fab molecule, as demonstrated by relative affinity determinations and competition experiments. This new method is suitable for extensive utilization in immunological experimental work using recombinant Fabs.