Insertion mutagenesis of the Pseudomonas aeruginosa phosphate-specific porin OprP

The gene encoding the Pseudomonas aeruginosa phosphate-specific porin OprP was subjected to both linker and epitope insertion mutageneses. Nine of the 13 linker mutant genes expressed protein at levels comparable to those obtained with the wild-type gene. These mutant proteins were shown, by indirect immunofluorescence with an OprP-specific antiserum, to be properly exposed at the cell surface. Four of the linker mutant genes expressed protein at reduced levels which were not detectable at the cell surface. A foreign epitope from the circumsporozoite form of the malarial parasite Plasmodium falciparum was cloned into the linker sites of 12 of the 13 mutant genes. Seven of the resultant epitope insertion mutant genes expressed surface-exposed protein. Two of these mutant genes presented the foreign epitope at surface-accessible regions as assessed by indirect immunofluorescence with a malarial epitope-specific monoclonal antibody. The data from these experiments were used to create a topological model of the OprP monomer.