Integrated Bioinformatic and Targeted Deletion Analyses of the SRS Gene Superfamily Identify SRS29C as a Negative Regulator of Toxoplasma Virulence

Program in Molecular Structure and Function, Hospital for Sick Children, Toronto, Ontario, Canada.
mBio (Impact Factor: 6.79). 10/2012; 3(6). DOI: 10.1128/mBio.00321-12
Source: PubMed


The Toxoplasma gondii SRS gene superfamily is structurally related to SRS29B (formerly SAG1), a surface adhesin that binds host cells and stimulates host immunity. Comparative genomic analyses of three Toxoplasma strains identified 182 SRS genes distributed across 14 chromosomes at 57 genomic loci. Eight distinct SRS subfamilies were resolved. A core 69 functional gene orthologs were identified, and strain-specific expansions and pseudogenization were common. Gene expression profiling demonstrated differential expression of SRS genes in a developmental-stage- and strain-specific fashion and identified nine SRS genes as priority targets for gene deletion among the tissue-encysting coccidia. A Δsag1 sag2A mutant was significantly attenuated in murine acute virulence and showed upregulated SRS29C (formerly SRS2) expression. Transgenic overexpression of SRS29C in the virulent RH parent was similarly attenuated. Together, these findings reveal SRS29C to be an important regulator of acute virulence in mice and demonstrate the power of integrated genomic analysis to guide experimental investigations.

Parasitic species employ large gene families to subvert host immunity to enable pathogen colonization and cause disease. Toxoplasma gondii contains a large surface coat gene superfamily that encodes adhesins and virulence factors that facilitate infection in susceptible hosts. We generated an integrated bioinformatic resource to predict which genes from within this 182-gene superfamily of adhesin-encoding genes play an essential role in the host-pathogen interaction. Targeted gene deletion experiments with predicted candidate surface antigens identified SRS29C as an important negative regulator of acute virulence in murine models of Toxoplasma infection. Our integrated computational and experimental approach provides a comprehensive framework, or road map, for the assembly and discovery of additional key pathogenesis genes contained within other large surface coat gene superfamilies from a broad array of eukaryotic pathogens.

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    • "Toxoplasma contains several distinct, coccidian-specific multicopy gene families throughout its genome, including those that encode the SRS, ROPK, and SUSA proteins [51-53]. Recently, a bioinformatics study showed that 60 out of the 144 ME49 SRS genes (42%) are located in subtelomeric sites [54]. However, none of these genes are near TgTAS-like regions in the current genome assembly. "
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    • "Compared to Type II and Type III, Type I strains display relatively high growth rates and are acutely virulent in mice (LD 100 ¼1 parasite) (Howe and Sibley, 1995). Recent work has identified that murine virulence is highly dependent on the expression level of virulence factors, such as ROP18, GRA15, and SRS29C (Melo et al, 2011; Wasmuth et al, 2012), proteins that target host immune signalling pathways. At the same time, due to its importance in providing energy and the basic building blocks required for growth, metabolic potential is increasingly being viewed as a critical element governing a pathogen's virulence potential, as well as its ability to survive in infected hosts (McKinney et al, 2000; Olszewski et al, 2009; Willger et al, 2009; Ensminger et al, 2012). "
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