Got mutants? How advances in chlamydial genetics have furthered the study of effector proteins

Abstract

Chlamydia trachomatis is the leading cause of infectious blindness and a sexually transmitted infection. All chlamydiae are obligate intracellular bacteria that replicate within a membrane-bound vacuole termed the inclusion. From the confines of the inclusion, the bacteria must interact with many host organelles to acquire key nutrients necessary for replication, all while promoting host cell viability and subverting host defense mechanisms. To achieve these feats, C. trachomatis delivers an arsenal of virulence factors into the eukaryotic cell via a type 3 secretion system (T3SS) which facilitates invasion, manipulation of host vesicular trafficking, subversion of host defense mechanisms, and promotes bacteria egress at the conclusion of the developmental cycle. A subset of these proteins intercalate into the inclusion and are thus referred to as inclusion membrane proteins. Whereas others, referred to as conventional T3SS effectors, are released into the host cell where they localize to various eukaryotic organelles or remain in the cytosol. Here, we discuss the functions of T3SS effector proteins with a focus on how advances in chlamydial genetics have facilitated the identification and molecular characterization of these important factors.

Chlamydia trachomatis effector Dre1 interacts with dynactin to reposition host organelles during infection

“…Many Incs, including CT101, CT222, IPAM, CT224, CT228, IncB, IncC, CT288, and CT850 localize at discrete microdomains on the inclusion membrane that are enriched in cholesterol, active Src-family kinases and MTs (Mital et al, 2010; Weber et al, 2015), and co-localize with the centrosome (Mital et al, 2010). Of the Incs found at these microdomains, many have been shown to directly or indirectly bind centrosomal proteins (Almeida et al, 2018; Andersen et al, 2021; Dumoux et al, 2015). Given the reduced genome size of C. trachomatis , this represents a striking number of effectors associated with a single organelle.…”

“…These algorithms prioritize interactions based on their reproducibility, abundance, and specificity. Three dynactin subunits that co-purified with Dre1 (CapZa, CapZb, and beta-actin) were not in the top 5% of MiST scores, likely because their specificity scores were penalized due to their interactions with actin filaments which are also regulated by other Incs (Andersen et. al., 2021, Elwell et.…”

“…As many of these host cell structures are arrayed around the centrosome, an intimate association with the centrosome would provide the physical opportunity for the inclusion to interact with host compartments and obtain the nutrients required to facilitate intracellular growth. Indeed, Chlamydia selectively repositions actin, MTs, the mitotic spindle, GA, ER, and lipid droplets around the developing inclusion during infection, though a detailed understanding of how bacterial and host proteins facilitate this massive host cell reorganization remains elusive (Andersen et al, 2021; Elwell et al, 2016).…”

The Chlamydia trachomatis type III secreted effector protein CteG induces centrosome amplification through interactions with centrin-2

“…The copyright holder for this preprint this version posted June 23, 2022. ; https://doi.org/10.1101/2022.06. 23.496711 doi: bioRxiv preprint HPV infection are characterized by multipolar spindles, which is linked to abnormal centrosome number (12). The HPV oncoprotein E7 induces centrosome amplification by targeting centriole duplication, which can lead to centrosome accumulation and ultimately causes genomic instability.…”

Lawsonia intracellularis LI0666 is a new EPIYA effector exported by the Yersinia enterocolitica type III secretion system

“…While the expression of some components of this putative T3SS has been detected during experimental infection, the microaerophilic obligate intracellular lifestyle and the genetic dissimilarity between L. intracellularis and other enteric pathogens have hampered the identification of potential T3SS substrates (effector proteins) [ 5 ]. Intracellular bacteria typically require the activity of many effector proteins to remodel the host environment and establish a replicative niche, as exemplified by Chlamydia spp [ 6 ], which suggests that effector proteins play a significant role in the pathogenesis of L. intracellularis . Given the challenges of culturing L. intracellularis under laboratory conditions, currently the most feasible method for effector protein identification is the use of a surrogate system.…”