The Chlamydia pneumoniae Tarp Ortholog CPn0572 Stabilizes Host F-Actin by Displacement of Cofilin

Abstract

Pathogenic <i>Chlamydia</i> species force entry into human cells via specific adhesin-receptor interactions and subsequently secrete effector proteins into the host cytoplasm, which in turn modulate host-cell processes to promote infection. One such effector, the <i>C. trachomatis</i> Tarp factor, nucleates actin polymerization <i>in vitro</i>. Here we show that its <i>C. pneumoniae</i> ortholog, CPn0572, associates with actin patches upon bacterial invasion. GFP-CPn0572 ectopically expressed in yeast and human cells co-localizes with actin patches and distinctly aberrantly thickened and extended actin cables. A 59-aa DUF 1547 (DUF) domain, which overlaps with the minimal actin-binding and protein oligomerization fragment required for actin nucleation in other Tarp orthologs, is responsible for the aberrant actin phenotype in yeast. Interestingly, GFP-CPn0572 in human cells associated with and led to the formation of non-actin microfilaments. This phenotype is strongly enhanced in human cells expressing the GFP-tagged DUF deletion variant (GFP-ΔDUF). Finally ectopic CPn0572 expression in yeast and <i>in-vitro</i> actin filament binding assays, demonstrated that CPn0572 stabilizes pre-assembled F-actin by displacing and/or inhibiting binding of the actin-severing protein cofilin. Remarkably, the DUF domain suffices to displace cofilin from F actin. Thus, in addition to its actin-nucleating activities, the <i>C. pneumoniae</i> CPn0572 also stabilizes preformed host actin filaments.