Expression, Purification and preliminary X-Ray diffraction of a pathogenic bacterial protease from Stenotrophomonas maltophilia

Many pathogenic bacteria produce extracellular proteases, which are considered to be virulent factors that attack and degrade the host tissues, thus being involved in the pathogenesis of various diseases. One such bacterium is Stenotrophomonas maltophilia which increasingly emerges as a multi-resistant hospital germ. It is already known to be multidrug-resistant, thus causing difficulties in its treatment. Here, we report the expression, purification, crystallization and initial diffraction data collection of the major secretory protease from S. maltophilia (StmPr1). StmPr1 was expressed in E. coli and remarkably it was processed by the host bacteria as a core protein of 36 kDa, which was fully active and could be crystallized. An effective purification protocol was established. StmPr1 was crystallized applying the hanging drop vapor method using 1.8 M ammonium sulphate and 100mM Tris-HCl buffer pH 7. Crystals diffracted to a resolution of 1.4 Å applying synchrotron radiation. Unit-cell parameters were calculated to be a = 60.43 Å, b = 86.51 Å and c = 132.20 Å corresponding to the orthorhombic space group C2221 with one molecule in the asymmetric unit. This basic knowledge for the expression, purification, crystallization and initial diffraction data collection of StmPr1 will be useful for obtaining high resolution X-ray structure analysis of StmPr1 and the investigation of its functional properties.