Expression, purification and preliminary crystallographic analysis of oligopeptidase B from Trypanosoma brucei

African sleeping sickness, also called trypanosomiasis, is a significant cause of morbidity and mortality in sub-Saharan Africa. Peptidases from Trypanosoma brucei, the causative agent, include the serine peptidase oligopeptidase B, a documented virulence factor and therapeutic target. Determination of the three-dimensional structure of oligopeptidase B is desirable to facilitate the development of novel inhibitors. Oligopeptidase B was overexpressed in Escherichia coli as an N-terminally hexahistidine-tagged fusion protein, purified using metal-affinity chromatography and crystallized using the hanging-drop vapour-diffusion technique in 7%(w/v) polyethylene glycol 6000, 1 M LiCl, 0.1 M bis-tris propane pH 7.5. Diffraction data to 2.7 angstroms resolution were collected using synchrotron radiation. The crystals belong to space group P3(1)21 or P3(2)21, with unit-cell parameters a = b = 124.5, c = 249.9 angstroms. A complete data set to 2.7 angstroms was collected using synchrotron radiation.