Different crystal forms of the C23A mutant from the leader proteinase of foot-and-mouth disease virus were obtained by the hanging drop vapor diffusion technique, using MgCl2 and PEG 6000 as precipitants. Well-developed crystals, with cubic morphology growing to approximately 1.0 mm(3) in size, presented a large unit cell parameter of 274.5 Angstrom and diffracted to, at most, 5 Angstrom resolution. A second type of crystal had a tetragonal appearance and these were obtained in droplets soaked in a silica gel matrix. These crystals, with an approximate size of 0.3 X 0.3 X 0.7 mm(3), diffracted to approximately 4.0 Angstrom resolution, but presented a strong anisotropic mosaicity around the longest crystal axis. Crystals with a needlelike morphology and reaching sizes of about 0.2 X 0.3 X 1.2 mm(3) diffracted beyond 3.5 Angstrom resolution and were stable to X-ray radiation for approximately one day when using a conventional source at room temperature. These crystals are orthorhombic with space group 1222 (or I2(1)2(1)2(1)) and unit cell dimensions a = 65.9 Angstrom, b = 104.3 Angstrom, and c = 124.0 Angstrom, and appear well suited for high-resolution studies. Density packing considerations are consistent with the presence of two molecules in the asymmetric unit and a solvent content of approximately 54%.
