Chlamydia trachomatis secretion of an immunodominant hypothetical protein (CT795) into host cell cytoplasm

The Chlamydia-specific hypothetical protein CT795 was dominantly recognized by human antisera produced during C. trachomatis infection but not by animal antisera raised against dead chlamydia organisms. The immundominant region recognized by the human antibodies was mapped to the N-terminal fragment T22-S69. The endogenous CT795 was detected in the cytoplasm of host cells during C. trachomatis infection and was highly enriched in the host cytosolic fraction but absent in the purified chlamydia organisms, suggesting that CT795 is synthesized and secreted into host cell cytoplasm without incorporation into the organisms. All C. trachomatis serovars tested secreted CT795. A predicted signal peptide of CT795 directed the mature PhoA to cross Escherichia coli inner membranes. The secretion of CT795 in Chlamydia-infected cells was inhibited by a C(16) compound targeting signal peptidase I, but not by a C(1) compound known to block the type III secretion pathway. These results suggest that CT795, like CPAF (a Chlamydia-secreted virulence factor), is secreted into the host cell cytoplasm via a sec-dependent mechanism and not by a type III secretion pathway. The above characterizations of CT795 have provided important information for further understanding the potential roles of CT795 in C. trachomatis pathogenesis.