Crystallization of rat procathepsin B

Rat procathepsin B has been expressed in the yeast Pichia pastoris. To facilitate crystallization of the proform two mutations were introduced: Cys29Ser to avoid self-processing and Ser115Ala to eliminate an N-glycosylation site. The recombinant protein was purified and crystallized by vapor diffusion against mother liquor containing 100 mM KSCN, 100 mM phosphate buffer, pH 6.5 and polyethylene glycol (PEG) 3350 as a precipitating agent. Crystal size was increased by multiple macroseeding. At a 16% PEG concentration trigonal crystals were obtained, with the space group P3(1)21 and a = 99.6, c = 141.4 A, gamma = 120 degrees. They diffract to 2.8 A resolution using a rotating-anode source. At a concentration of 11% PEG, rod-shaped crystals were grown. They are monoclinic, space group P2(1), a = 62.8, b = 67.9, c = 100.4 A, beta = 98.2 degrees and diffract to approximately 3.5 A.