Biological Characterization of Chlamydia trachomatis Plasticity Zone MACPF Domain Family Protein CT153

Chlamydia trachomatis strains are obligate intracellular human pathogens that share near genomic synteny but have distinct infection and disease organotropisms. The genetic basis for differences in the pathogen-host relationship among chlamydial strains is linked to a variable region of chlamydial genomes, termed the plasticity zone (PZ). Two groups of PZ-encoded proteins, the membrane attack complex/perforin (MACPF) domain protein (CT153) and members of the phospholipase D-like (PLD) family, are related to proteins that modify membranes and lipids, but the functions of CT153 and the PZ PLDs (pzPLDs) are unknown. Here, we show that full-length CT153 (p91) was present in the elementary bodies (EBs) of 15 C. trachomatis reference strains. CT153 underwent a rapid infection-dependent proteolytic cleavage into polypeptides of 57 and 41 kDa that was independent of de novo chlamydial protein synthesis. Following productive infection, p91 was expressed during the mid-developmental cycle and was similarly processed into p57 and p41 fragments. Infected-cell fractionation studies showed that insoluble fractions contained p91, p57, and p41, whereas only p91 was found in the soluble fraction, indicating that unprocessed CT153 may be secreted. Finally, CT153 localized to a distinct population of reticulate bodies, some of which were in contact with the inclusion membrane.