A Type III Secretion System in Vibrio cholerae Translocates a Formin/Spire Hybrid-like Actin Nucleator to Promote Intestinal Colonization

Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
Cell host & microbe (Impact Factor: 12.33). 05/2007; 1(2):95-107. DOI: 10.1016/j.chom.2007.03.005
Source: PubMed


We have previously characterized a non-O1, non-O139 Vibrio cholerae strain, AM-19226, that lacks the known virulence factors but contains components of a type III secretion system (T3SS). In this study, we demonstrated that the T3SS is functional and is required for intestinal colonization in the infant mouse model. We also identified VopF, which is conserved among T3SS-positive V. cholerae strains, as an effector containing both formin homology 1-like (FH1-like) and WASP homology 2 (WH2) domains. Translocation of VopF by V. cholerae or expression by transfection altered the actin cytoskeletal organization of the eukaryotic host cells. In vitro domain analysis indicated that both FH1-like and WH2 domains are required for actin nucleation and polymerization activity. These data correlate with in vivo data, suggesting that VopF-mediated alteration of actin polymerization homeostasis is required for efficient intestinal colonization by T3SS+V. cholerae in the infant mouse model.

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Available from: Vincent Tam, Mar 28, 2014
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    • "The activity of the VopL and VopF actin nucleators has been linked to enterotoxic effects during infection. Vibrio parahaemolyticus VopL disrupts actin homeostasis by inducing the formation of large stress fibres in infected cells (Liverman et al. 2007), while VopF mediates the formation of aberrant protrusions on the surface and periphery of the cells and localizes at the tip of these protrusions, bound to the barbed end of the growing microfilaments (Tam et al. 2007) (Fig. 3). These cytoskeletal rearrangements have implications in the alteration of actin homeostasis during infection, leading to a decrease in transepithelial resistance and to the increase in diarrhoea. "
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    ABSTRACT: The actin cytoskeleton is a key target of numerous microbial pathogens, including protozoa, fungi, bacteria, and viruses. In particular, bacterial pathogens produce and deliver virulence effector proteins that hijack actin dynamics to enable bacterial invasion of host cells, allow movement within the host cytosol, facilitate intercellular spread, or block phagocytosis. Many of these effector proteins directly or indirectly target the major eukaryotic actin nucleator, the Arp2/3 complex, by either mimicking Nucleation Promoting Factors or activating upstream small GTPases. In contrast, this review is focused on a recently identified class of effector proteins from Gram-negative bacteria that function as direct actin nucleators. These effector proteins mimic functional activities of formins, WH2-nucleators, and Ena/VASP assembly promoting factors demonstrating that bacteria have co-opted the complete set of eukaryotic actin assembly pathways. Structural and functional analyses of these nucleators have revealed several motifs and/or mechanistic activities that are shared with eukaryotic actin nucleators. However, functional effects of these proteins during infection extend beyond plain actin polymerization leading to interference with other host cell functions such as vesicle trafficking, cell cycle progression, and cell death. Therefore, their use as model systems could not only help in the understanding of the mechanistic details of actin polymerization but also provide novel insights into the connection between actin dynamics and other cellular pathways.
    Full-text · Article · Sep 2015 · Pathogens and Disease
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    • "Dimerization via the VCD brings together six WH2 motifs and enhances nucleation activity. V. cholerae possesses similar actin nucleating effector, VopF and VopN (Tam et al., 2007; 2010). Unlike VopL, VopF induces actin-rich filoform from the periphery of the cells and localizes unbranched actin-rich protrusions. "
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    ABSTRACT: Vibrio parahaemolyticus is a leading causative agent of seafood-borne gastroenteritis worldwide. Most clinical isolates from patients with diarrhea possess two sets of genes for the type III secretion system (T3SS) on each chromosome (T3SS1 and T3SS2). T3SS is a protein secretion system that delivers effector proteins directly into eukaryotic cells. The injected effectors modify the normal cell functions by altering or disrupting the normal cell signaling pathways. Of the two sets of T3SS genes present in V. parahaemolyticus, T3SS2 is essential for enterotoxicity in several animal models. Recent studies have elucidated the biological activities of several T3SS2 effectors and their roles in virulence. This review focuses on the regulation of T3SS2 gene expression and T3SS2 effectors that specifically target the actin cytoskeleton.
    Preview · Article · Dec 2014 · Cellular Microbiology
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    • "VopF and its ortholog VopL are pathogen effectors that are injected in host eukaryotic cells by the T3SS secretion system of Vibrio cholerae and Vibrio parahaemolyticus, respectively . Once internalized, VopF and VopL harness the actin cytoskeleton of the host and induce filopodia and stress fibers, respectively [Liverman et al., 2007; Tam et al., 2007]. These proteins are made of three adjacent WH2 domains assembled in a homodimer by a C-terminal dimerization domain, whose crystal structure has been solved in VopL [Namgoong et al., 2011; Yu et al., 2011]. "
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    ABSTRACT: WH2 domains are multifunctional regulators of actin assembly that can either sequester G-actin or allow polarized barbed end growth. They all bind similarly to a hydrophobic pocket at the barbed face of actin. Depending on their electrostatic environment, WH2 domains can nucleate actin assembly by facilitating the formation of pre-nuclei dimers along the canonical spontaneous assembly pathway. They also modulate filament barbed end dynamics in a versatile fashion, acting either as barbed end cappers or assisting barbed end growth like profilin or uncapping barbed ends and potentially mediating processive elongation like formins when they are dimerized. Tandem repeats of WH2 domains can sever filaments and either remain bound to created barbed ends like gelsolin, or strip off an ADP-actin subunit from the severed polymer end, depending on their relative affinity for terminal ADP-F-actin or ADP-G-actin. In summary, WH2 domains recapitulate all known elementary regulatory functions so far found in individual actin-binding proteins. By combining different discrete sets of these multifunctional properties, they acquire specific functions in various actin-based processes, and participate in activities as diverse as filament branching, filopodia extension, or actin remodeling in ciliogenesis and asymmetric meiotic division. They also integrate these functions with other actin-binding motifs present either in the same protein or in a complex with another protein, expanding the range of complexity in actin regulation. The details of their molecular mechanisms and the underlying structural basis provide exciting avenues in actin research. © 2013 Wiley Periodicals, Inc.
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