Cloning, expression, crystallization and preliminary X-ray diffraction studies of staphylococcal superantigen-like protein 1 (SSL1)

Staphylococcus aureus produces a family of exotoxins which are structural homologues of superantigens and thus are called staphylococcal superantigen-like proteins (SSLs). Amongst the 14 SSL genes, ssl1 (SAOUHSC_00383) has been cloned in the pQE30 expression vector, overexpressed in Escherichia coli M15 (pREP4) cells and the protein purified to homogeneity. The protein was crystallized using 6% Tacsimate pH 6.0, 0.1 M MES pH 6.0, 25%(w/v) polyethylene glycol 3350, 100 mM NDSB 256 at 298 K by the sitting-drop vapour-diffusion method. The crystals belonged to space group P2₁, with unit-cell parameters a = 77.9, b = 70.5, c = 126.5 Å, β = 106.2°. X-ray diffraction data were collected and processed to a maximum resolution of 2.5 Å. The crystal contains six molecules in the asymmetric unit.