Abstract
The translocated actin recruiting phosphoprotein (Tarp) is conserved among all pathogenic chlamydial species. Previous reports identified single C. trachomatis Tarp actin binding and proline rich domains required for Tarp mediated actin nucleation. A peptide antiserum specific for the Tarp actin binding domain was generated and inhibited actin polymerization in vitro and C. trachomatis entry in vivo, indicating an essential role for Tarp in chlamydial pathogenesis. Sequence analysis of Tarp orthologs from additional chlamydial species and C. trachomatis serovars indicated multiple putative actin binding sites. In order to determine whether the identified actin binding domains are functionally conserved, GST-Tarp fusions from multiple chlamydial species were examined for their ability to bind and nucleate actin. Chlamydial Tarps harbored variable numbers of actin binding sites and promoted actin nucleation as determined by in vitro polymerization assays. Our findings indicate that Tarp mediated actin binding and nucleation is a conserved feature among diverse chlamydial species and this function plays a critical role in bacterial invasion of host cells.
Highlights
The obligate intracellular gram negative bacterium, Chlamydia trachomatis, is the most frequently reported sexually transmitted disease in the United States and the leading cause of preventable blindness worldwide [1]
We demonstrate here that translocated actin recruiting phosphoprotein (Tarp) orthologs from Chlamydia pneumonia, C. caviae, C. muridarum and various C. trachomatis serovars all harbor at least one and up to four functional actin binding domains and that purified recombinant Tarps from all chlamydial species were capable of nucleating actin filament formation in vitro
The induction of cytoskeletal rearrangements to promote chlamydial internalization is partially mediated by a type III secreted effector protein called Tarp that is translocated upon contact with host cells and independently nucleates actin filament formation
Summary
The obligate intracellular gram negative bacterium, Chlamydia trachomatis, is the most frequently reported sexually transmitted disease in the United States and the leading cause of preventable blindness worldwide [1]. The exact mechanisms of chlamydial attachment and entry of nonphagocytic cells are unclear, but certain features, such as the recruitment of actin to the site of attachment, are conserved among all chlamydial species examined far [3]. Drugs such as cytochalasin D that prevent actin polymerization inhibit infection [3,4,5,6,7]. Sequence analysis of all known Tarp orthologs indicate that the proline rich domain and actin binding alpha helix are conserved the tyrosine-rich repeat domain is absent from C. caviae, C. muridarum, and C. pneumoniae [16]
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