Biological function study on surface antigen-related protein Tgsrs51 of Toxoplasma gondii

<bold>Objective</bold> <italic>Toxoplasma gondii</italic> is an obligate intracellular protozoan parasite that infects all warm-blooded animals，including humans.Currently，there is a lack of specific drugs for the treatment of toxoplasmosis，and traditional drug therapy faces issues such as significant toxic side effects and limited efficacy.Therefore，developing a safe and effective vaccine has become an important strategy for preventing and controlling the disease.Surface antigen-related sequence proteins（SRSs）of <italic>T. gondii</italic> play a crucial role in virulence，invasion and adhesion，and immune regulation of the parasite.Among them，SRS51 protein（TGME49_308840），as a member of the SRS family，has potential research value due to its unclear specific biological function.This study aims to explore the biological function and mechanism of action of <italic>Toxoplasma gondii</italic> SRS51 protein，providing a reference for the development of safe and effective <italic>T. gondii</italic> vaccines. <bold>Method</bold> With the <italic>Toxoplasma gondii</italic> type II Pru strain as the subject，CRISPR-Cas9 gene editing and seamless cloning techniques were employed to construct a <italic>Tgsrs51</italic> gene-deleted strain（PruΔsrs51）.The biological function of the Toxoplasma SRS51 protein was systematically evaluated through plaque assay，cell invasion and proliferation assay，escape assay，<italic>in vitro</italic> bradyzoite conversion assay，and mouse virulence assay. <bold>Result</bold> After the deletion of the <italic>Tgsrs51</italic> gene，the plaque area and number of <italic>T. gondii</italic> significantly decreased（<italic>P</italic>&lt;0.000 1）.The deletion of the <italic>Tgsrs51</italic> gene caused a decrease in MIC2 protein expression.The invasion and proliferation abilities were significantly reduced（<italic>P</italic>&lt;0.001）.The pathogenicity to mice also weakened（<italic>P</italic>&lt;0.05），but it did not affect the escape ability and <italic>in vitro</italic> tachyzoite transformation of the parasite（<italic>P</italic>&gt;0.05）. <bold>Conclusion</bold> SRS51 protein deletion significantly reduces acute virulence and chronic cyst formation.It can be considered as a candidate gene for a weakened <italic>T. gondii</italic> vaccine.