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 P 2 1 , with unit‐cell parameters a = 42.9, b = 74.8, c = 116.5 Å, β = 93.0°, and diffracted to 2.6 Å resolution using synchrotron radiation. Assuming the presence of two molecules in the asymmetric unit, the calculated Matthews coefficient is 2.28 Å 3  Da −1 , corresponding to a solvent content of 46%. Initial attempts to solve the structure using molecular‐replacement techniques were successful.