Abstract
Since intracellular survival of all chlamydiae depends on the manipulation of the host cell through type III secreted effector proteins, their characterization is crucial for the understanding of chlamydial pathogenesis. We functionally characterized the putative type III secreted Chlamydia abortus protein CAB063, describe its intracellular localization and identified pro- and eukaryotic binding partners. Based on an experimental infection model and plasmid transfections, we investigated the subcellular localization of CAB063 by immunofluorescence microscopy, immunoelectron microscopy, and Western blot analysis. Pro- and eukaryotic targets were identified by co-immunofluorescence, co-immunoprecipitation, and mass spectrometry. Transmission electron microscopy and flow cytometry were used for morphological and functional investigations on host cell apoptosis. CAB063 localized in the nuclear membrane of the host cell nucleus and we identified the chaperone HSP70 and lamin A/C as pro- and eukaryotic targets, respectively. CAB063-dependent morphological alterations of the host cell nucleus correlated with increased apoptosis rates of infected and CAB063-transfected cells. We provide evidence that CAB063 is a chaperone-folded type III secreted C. abortus virulence factor that targets lamin thereby altering the host cell nuclear membrane structure. This process may be responsible for an increased apoptosis rate at the end of the chlamydial developmental cycle, at which CAB063 is physiologically expressed.
Highlights
Chlamydia (C.) abortus is a zooanthroponotic pathogen common in ruminants (Essig and Longbottom, 2015), in which it causes enzootic abortions of ewes (EAE) and accounts for considerable economic damage (Longbottom and Coulter, 2003)
Thereby, we could confirm previous work in which we found CAB063 to localize both in the chlamydial inclusion and the host cell nucleus (Forsbach-Birk et al, 2013) (Figure 1A)
We investigated the putative virulence-associated protein CAB063 for its intracellular localization, its pro- and eukaryotic targets as well as its functional role in C. abortus infection
Summary
Chlamydia (C.) abortus is a zooanthroponotic pathogen common in ruminants (Essig and Longbottom, 2015), in which it causes enzootic abortions of ewes (EAE) and accounts for considerable economic damage (Longbottom and Coulter, 2003). A well-known strategy of intracellular pathogens is the delivery of type III secreted effector proteins to the host cell cytosol, where they serve the purpose of virulence attainment and host cell manipulation (Cosse et al, 2018). Since these effectors have to be passed through the membrane of the intracellular compartment referred to as an inclusion, a sophisticated type III secretion needle apparatus is required (Nans et al, 2015b). The identification of proand eukaryotic binding partners helped to elucidate potential functions of CAB063 in chlamydial infections
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