A hybrid outer membrane protein antigen for vaccination against Pseudomonas aeruginosa

Recently a hybrid protein containing parts of the outer membrane proteins OprF (aa 190-342) and OprI (aa 21-83) from Pseudomonas aeruginosa fused to the glutathione-S-transferase was shown to protect mice against a 975-fold 50% lethal dose of P. aeruginosa. To omit the use of the GST-protein, the hybrid protein OprF-OprI was expressed in E. coli using distinct modifications which have not to be eliminated after its expression. Using different signal peptides, the yield of the hybrid protein OprF-OprI in E. coli could be increased to 30% of the total cell protein, however, only a very small amount of the hybrid preprotein was processed and could be isolated from the periplasm of the host. A construct containing an N-terminal extension of 11 amino acids from the original OprF gene gave rise to a significantly higher expression in the cytoplasm. Purification was facilitated by the addition of a five histidine tag at the C-terminus. An even higher expression was obtained by a construct in which a six histidine tag was attached to the N-terminus of the hybrid protein. The N-terminal extended OprF-OprI as well as the N-terminal his-tagged OprF-OprI hybrid antigens were purified by immobilized-metal affinity chromatography under native and denaturing conditions and can now be tested for protectivity against P. aeruginosa in animal model systems.