Chlamydial TARP is a bacterial nucleator of actin

Abstract

Chlamydia trachomatis entry into host cells results from a parasitedirected remodeling of the actin cytoskeleton. A type III secreted effector, TARP (translocated actin recruiting phosphoprotein), has been implicated in the recruitment of actin to the site of internalization. To elucidate the role of TARP in actin recruitment, we identified host cell proteins that associated with recombinant GST-TARP fusions. TARP directly associated with actin, and this interaction promoted actin nucleation as determined by in vitro polymerization assays. Domain analysis of TARP identified an actin-binding domain that bears structural and primary amino acid sequence similarity to WH2 domain family proteins. In addition, a proline-rich domain was found to promote TARP oligomerization and was required for TARP-dependent nucleation of new actin filaments. Our findings reveal a mechanism by which chlamydiae induce localized cytoskeletal changes by the translocated effector TARP during entry into host cells.Chlamydia ͉ type III secretion ͉ cytoskeleton ͉ endocytosis A Gram-negative obligate intracellular bacterium, Chlamydia trachomatis, is the leading cause of preventable blindness worldwide and the most prevalent bacterial pathogen causing sexually transmitted disease in the western world (1). Chlamydiae initiate their intracellular developmental cycle by actively gaining entry into host cells. The extracellular infectious form of the developmental cycle is referred to as an elementary body (EB). Once engulfed by the host cell, the EB differentiates into the replicative reticulate body within the protective confines of a membrane-bound parasitophorous vacuole called an inclusion (2).The ligands on the EB surface and cognate host cell receptor have not been definitively identified; however, it appears that chlamydiae use an entry mechanism that involves several distinct levels of interaction (3, 4). EB invasion of nonphagocytic cells is thus the product of coordinated cytoskeletal remodeling characterized by the formation of pedestal-like structures and hypertrophic microvilli that are directly triggered by the invading chlamydiae (5).A recently identified C. trachomatis type III secretion system secreted protein called TARP (for translocated actin recruiting phosphoprotein) is tyrosine-phosphorylated by a host cell kinase and is spatially and temporally associated with the recruitment of actin at the site of EB invasion (6). TARP is present in all pathogenic Chlamydia species examined to date. Analysis of TARP orthologs from C. trachomatis, Chlamydia muridarium, Chlamydia caviae, and Chlamydia pneumoniae indicates that only C. trachomatis serovars are phosphorylated, despite all Chlamydia strains demonstrating the recruitment of actin to the site of entry (6, 7).We demonstrate here that TARP associates directly with actin by a small domain contained within the C-terminal region of the protein. Furthermore, TARP independently nucleates new actin filaments by forming a large homogenous multimeric protein complex mediated by a prolin...

Host α-adducin is redistributed and localized to the inclusion membrane in Chlamydia- and Chlamydophila-infected cells

“…Chlamydiae manipulate cytoskeletal structures to facilitate entry (Jewett et al, 2006), redirect vesicular traffic (Scidmore et al, 1996a), and maintain chlamydia-filled inclusions in close proximity to the nucleus and other organelles (Grieshaber et al, 2003). The chlamydiainduced alteration of a-adducin and Raf-1 distribution described in this report may influence the interaction of these proteins with downstream substrates, perhaps contributing to chlamydial development and growth.…”

Approach to discover T- and B-cell antigens of intracellular pathogens applied to the design of Chlamydia trachomatis vaccines

“…Apart from TARP, a protein able to interact with actin and probably involved in chlamydial invasion (41), little is known about the roles of these proteins in Chlamydia biology. CT733/TC0106 is, thus far, an uncharacterized protein.…”

Arp2/3-independent assembly of actin by Vibrio type III effector VopL

“…Still other bacterial pathogens use virulence factors, such as ActA from Listeria, which encodes multiple PRMs to manipulate the eukaryotic nucleating factor Arp2/3 (39,40). The TARP protein from Chlamydia contains only one WH2 domain and is less potent than VopL in in vitro actin assembly assays (41). In addition, a family of bacterial G protein mimics have been identified that replicate signaling properties of Rho-like GTPase in manipulating the actin cytoskeleton (42).…”