EXPRESSION OF THE MAJOR OUTER-MEMBRANE PROTEIN OF CHLAMYDIA-TRACHOMATIS IN ESCHERICHIA-COLI

The major outer membrane protein (MOMP) of Chlamydia trachomatis was e xpressed in Escherichia coli. To assess whether it assembled into a co nformationally correct structure at the cell surface, we characterized the recombinant MOMP (rMOMP) by Western immunoblot analysis, indirect immunofluorescence, and immunoprecipitation with monoclonal antibodie s (MAbs) that recognize contiguous and conformational MOMP epitopes. W estern blot analysis showed that most of the rMOMP comigrated with aut hentic monomer MOMP, indicating that its signal peptide was recognized and cleaved by E. coli. The rMOMP could not be detected on the cell s urface of viable or formalin-killed E. coli organisms by indirect immu nofluorescence staining with a MAb specific for a MOMP contiguous epit ope. In contrast, the same MAb readily stained rMOMP-expressing E. col i cells that had been permeablized by methanol fixation. A MAb that re cognizes a conformational MOMP epitope and reacted strongly with forma lin- or methanol-fixed elementary bodies failed to stain formalin- or methanol-fixed E. coli expressing rMOMP. Moreover, this MAb did not im munoprecipitate rMOMP from expressing E. coli cells even though it pre cipitated the authentic protein from lysates of C. trachomatis element ary bodies. Therefore we concluded that rMOMP was not localized to the E. coli cell surface and was not recognizable by a conformation-depen dent antibody. These results indicate that rMOMP expressed by E. coli is unlikely to serve as an accurate model of MOMP structure and functi on. They also question the utility of rMOMP as a source of immunogen f or eliciting neutralizing antibodies against conformational antigenic sites of the protein.