Structural and biological characterization of Staphylococcus aureus enterotoxin O

NOLI TRUANT SOFÍA; FERNANDEZ LYNCH MJ; ANTONOGLOU M BELEN; SARRATEA M BELEN; DE MARZI MC; MALCHIODI EL; FERNANDEZ M

Buenos Aires

Congreso; IV LASID Meeting, LXIII Argentinean Immunology Society Meeting, II French-Argentinean Immunology Meeting; 2015

Sociedad Argentina de Inmunología

Superantigens (SAgs) are enterotoxins which bind in a non-classical way to TCR-MHC-II complexes inducing a peptide-non-specific proliferation of T-lymphocytes and a massive cytokine release. Staphylococcus aureus produces a wide range of enterotoxins, which cause toxic shock syndrome (TSS), a potentially lethal disorder. Glucocorticoids are the traditional treatment for TSS, but recently cases of SAgs inducing resistance were described.We have previously reported that autochthonous strains of S. aureus have high prevalence of the egc operon, which includes the genes seg, sei, sem, sen and seo. Initially, we studied the SAgs SEG and SEI, which display complementary biological activity. Here we characterize molecular and biologically the SAg SEO.Methods: SEO was cloned in pET26b, produced in E. coli and purified as a His-tagged protein. To test its superantigen activity and virulence, SEO was exposed to different cell cultures to evaluate proliferation by using [methyl-3H]thymidine, in the presence or absence of glucocorticoids. In addition, we modeled SEO three-dimensional structure based on its sequence similarity with SEA, using bioinformatics tools, mainly Modeller.Results: SEO shows: 1-Typical SAgs compact globular structure (QMEAN-score:0,535); 2-Cytotoxic effect upon macrophages´ precursors (reduction of 99% of viability); 3-Ability to activate peripheral blood mononuclear cells (>25 times); 4-Capacity to induce resistance to glucocorticoid treatment.Conclusions: SEO appears to be a new virulence factor, exhibiting superantigen activity at the innate immunity level and showing resistance to the conventional treatment of corticoids for SAgs related diseases, similar to that observed for other SAgs of this operon.