Abstract
Chlamydia pneumoniae is an intracellular Gram-negative bacterium that possesses a type III secretion system (T3SS), which enables the pathogen to deliver, in a single step, effector proteins for modulation of host-cell functions into the human host cell cytosol to establish a unique intracellular niche for replication. The translocon proteins located at the top of the T3SS needle filament are essential for its function, as they form pores in the host-cell membrane. Interestingly, unlike other Gram-negative bacteria, C. pneumoniae has two putative translocon operons, named LcrH_1 and LcrH_2. However, little is known about chlamydial translocon proteins. In this study, we analyzed CPn0809, one of the putative hydrophobic translocators encoded by the LcrH_1 operon, and identified an ‘SseC-like family’ domain characteristic of T3S translocators. Using bright-field and confocal microscopy, we found that CPn0809 is associated with EBs during early and very late phases of a C. pneumoniae infection. Furthermore, CPn0809 forms oligomers, and interacts with the T3SS chaperone LcrH_1, via its N-terminal segment. Moreover, expression of full-length CPn0809 in the heterologous host Escherichia coli causes a grave cytotoxic effect that leads to cell death. Taken together, our data indicate that CPn0809 likely represents one of the translocon proteins of the C. pneumoniae T3SS, and possibly plays a role in the translocation of effector proteins in the early stages of infection.
Highlights
Chlamydia pneumoniae is an obligate intracellular Gram-negative pathogen that causes a wide range of pulmonary diseases
Like all Chlamydiae, C. pneumoniae is an obligate intracellular parasite with a unique biphasic life cycle, alternating between a metabolically inert infectious form called an elementary body (EB), which is adapted to survive in the hostile extracellular environment, and an intracellular form called the reticulate body (RB) that replicates by binary fission [5, 6]
Bioinformatic analysis suggests that CPn0809 harbors three hydrophobic domains (HD) in its C-terminal half, which are flanked by two coiled-coil domains (CC), while a third CC domain is located in the N-terminal segment (Fig 2)
Summary
Chlamydia pneumoniae is an obligate intracellular Gram-negative pathogen that causes a wide range of pulmonary diseases. Because these are often mild and atypical in character, it is thought that the bacterium’s contribution to the incidence of respiratory illness is significantly underestimated [1]. Like all Chlamydiae, C. pneumoniae is an obligate intracellular parasite with a unique biphasic life cycle, alternating between a metabolically inert infectious form called an elementary body (EB), which is adapted to survive in the hostile extracellular environment, and an intracellular form called the reticulate body (RB) that replicates by binary fission [5, 6]. PLOS ONE | DOI:10.1371/journal.pone.0148509 February 19, 2016
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