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Infection and Immunity, July 2005, p. 3860-3868, Vol. 73, No. 7
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.7.3860-3868.2005

Tyrosine Phosphorylation of the Chlamydial Effector Protein Tarp Is Species Specific and Not Required for Recruitment of Actin

Dawn R. Clifton ,^, Cheryl A. Dooley, Scott S. Grieshaber, Reynaldo A. Carabeo, Kenneth A. Fields,^¶ and Ted Hackstadt^*

Host-Parasite Interactions Section, Laboratory of Intracellular Parasites, Rocky Mountain Laboratories, NIAID, NIH, Hamilton, Montana 59840

Received 21 January 2005/ Returned for modification 15 February 2005/ Accepted 25 February 2005

Chlamydiae are obligate intracellular pathogens that efficiently induce their endocytosis by susceptible eukaryotic host cells. Recently, a Chlamydia trachomatis type III secreted effector protein, Tarp, was found to be translocated and tyrosine phosphorylated at the site of entry and associated with the recruitment of actin that coincides with endocytosis. C. trachomatis Tarp possesses up to six direct repeats of approximately 50 amino acids each. The majority of the tyrosine residues are found within this repeat region. Here we have ectopically expressed distinct domains of Tarp in HeLa 229 cells and demonstrated that tyrosine phosphorylation occurs primarily within the repeat region, while recruitment of actin is mediated by the C-terminal domain of the protein. A comparison of other sequenced chlamydial genomes revealed that each contains an ortholog of Tarp, although Chlamydia muridarum, Chlamydophila caviae, and Chlamydophila pneumoniae Tarp lack the large repeat region. Immunofluorescence and immunoblotting using an antiphosphotyrosine antibody show no evidence of phosphotyrosine at the site of entry of C. muridarum, C. caviae, and C. pneumoniae, although each species similarly recruits actin. Ectopic expression of full-length C. trachomatis and C. caviae Tarp confirmed that both recruit actin but only C. trachomatis Tarp is tyrosine phosphorylated. The data indicate that the C-terminal domain of Tarp is essential for actin recruitment and that tyrosine phosphorylation may not be an absolute requirement for actin recruitment. The results further suggest the potential for additional, unknown signal transduction pathways associated specifically with C. trachomatis.

Editor: D. L. Burns

These authors contributed equally to this work.

Present address: Department of Molecular Genetics and Biochemistry, University of Pittsburgh, Pittsburgh, PA 15261.

Present address: Department of Microbiology and Immunology, University of Louisville School of Medicine, Louisville, KY.

^¶ Present address: Department of Microbiology and Immunology, University of Miami School of Medicine, Miami, FL 33136.

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