Crystallization and preliminary X-ray diffraction studies of the precursor protein of a thermostable variant of papain

The crystallization of a recombinant thermostable variant of pro-papain has been carried out. The mutant pro-enzyme was expressed in Escherichia coli as inclusion bodies, refolded, purified and crystallized. The crystals belonged to space group P2(1), with unit-cell parameters a = 42.9, b = 74.8, c = 116.5 angstrom, beta = 93.0 degrees, and diffracted to 2.6 angstrom resolution using synchrotron radiation. Assuming the presence of two molecules in the asymmetric unit, the calculated Matthews coefficient is 2.28 angstrom(3) Da(-1), corresponding to a solvent content of 46%. Initial attempts to solve the structure using molecular-replacement techniques were successful.