Preliminary study on biological characterization of Chlamydia trachomatis plasmid protein p ^ORF5

Objective: To localize and characterize the plasmid protein p ^ORF5 in the Chlamydia trachomatis(Ct) infected cells. Methods: The open reading frame encoding for p ^ORF5 protein from the Ct plasmid was amplified and cloned into the p ^GEX-6p vector. The recombinant plasmid p ^GEX-p ^ORF5 was transformed into XL1-blue E. coli to express fusion protein with the glutathione-s-transferase (GST). After purified with Glutathione Sepharose 4B beads, the p ^ORF5 fusion protein was used to immunize mice to make monoclonal and polyclonal antibody. The antibodies were used to localize the endogenous p ^ORF5 protein and detect the expression pattern in Chlamydia-infected cells using an indirect immunofluorescence assay (IFA). At the same time, ELISA was used to determine whether p ^ORF5 plasmid protein was expressed and immunogenic during Ct infection in humans. Results: p ^ORF5 was detected a dominant signal in the cytosol of the Chlamydia-infected cells with a pattern similar to that of anti-CPAF. p ^ORF5 also appeared in the RBs and EBs in small quantity. Athough pattern was similarly, p ^ORF5 did not overlap with CPAF. p ^ORF5 protein was strongly recognized antiserum in an ELISA. Conclusion: The p ^ORF5 plasmid protein was identified as a secreted protein with good immunogenicity, p ^ORF5 gene was to express the endogenous target protein during human infection.