Crystallization and preliminary X-ray diffraction studies of trypsin-like proteases from the gastric fluid of the marine crab Cancer pagurus

The digestive fluid of the marine crab Cancer pagurus (Decapoda, Brachyura) contains highly stable proteases which display enhanced activity in aqueous mixtures of organic solvents. Three trypsins were isolated from the gastric fluid and two of them, C.p.TryII and C.p.TryIII, were purified to homogeneity by anion-exchange chromatography and crystallized by hanging-drop vapour diffusion. Diffraction data were collected at a synchrotron to 0.97 and 3.2 Å resolution, respectively. The crystal of C.p.TryII belongs to the orthorhombic space group P2₁2₁2₁, with unit-cell parameters a = 52.06, b = 62.00, c = 71.66 Å. Based on the Matthews coefficient, one protein molecule per asymmetric unit is suggested. In contrast, crystals of C.p.TryIII, which belong to the cubic space group P2 ₁3 with unit-cell parameters a = b = c = 215.4 Å, are assumed to contain 12 molecules per asymmetric unit.