An expression system for the E. coli fermentation of recombinant antibody [F.sub.ab] fragments from mice and rabbits

A mutually compatible vector system was developed for the bench-top fermenter production of mouse and rabbit [F.sub.ab] fragments comprising pASK85-pro-K411B and pASK85Rab-pro-WR13. These vectors provide a mouse- and rabbit-specific cloning site, respectively, the fefA promoter/operator and the proBA operon that complements the Pro biosynthetic deficiency of the Escherichia coli strain JM83 and can serve as an additional selection marker. Fermentation at elevated cell density ([OD.sub.600] = 20-40) of the atrazine-specific mouse [F.sub.ab] fragment K411B using JM83 harboring pASK85-pro-K411B in a 2 L bench-top vessel resulted in a yield of 240 µg/L x [OD.sub.600] affinity-purified protein (13.8 mg). In contrast, expression of leporid [F.sub.ab] fragments using pASK85Rab-pro-WR13 was unsuccessful due to the aggregation of rabbit light chains, which probably relates to a general problem of this specific class of immunoglobulins with their additional Cys residues. Coexpression of rabbit [F.sub.ab] fragments together with four periplasmic folding-helper proteins encoded on pTUM4 led to a significantly improved folding efficiency, resulting in a yield of 50 µg/L x [OD.sub.600] affinity-purified rabbit [F.sub.ab] fragment (3.3 mg) from the 2 L bench-top fermenter.