The 1.30 angstrom resolution structure of the Bacillus subtilis chorismatemutase catalytic homotrimer

The crystal structure of the Bacillus subtilis chorismate mutase, an enzyme of the aromatic amino acids biosynthetic pathway, was determined to 1.30 A ngstrom resolution. The structure of the homotrimer was determined by molec ular replacement using orthorhombic crystals of space group P2(1)2(1)2(1) w ith unit-cell parameters a = 52.2, b = 83.8, c = 86.0 Angstrom. The ABC tri mer of the monoclinic crystal structure [Chook et al. (1994), J. Mol. Biol. 240, 476-500] was used as the starting model. The final coordinates are co mposed of three complete polypeptide chains of 127 amino-acid residues. In addition, there are nine sulfate ions, five glycerol molecules and 424 wate r molecules clearly visible in the structure. This structure was refined wi th aniosotropic temperature factors, has excellent geometry and a crystallo graphic R factor of 0.169 with an R-free of 0.236. The three active sites o f the macromolecule are at the subunit interfaces, with residues from two s ubunits contributing to each site. This orthorhombic crystal form was grown using ammonium sulfate as the precipitant; glycerol was used as a cryoprot ectant during data collection. A glycerol molecule and sulfate ion in each of the active sites was found mimicking a transition-state analog. In this structure, the C-terminal tails of the subunits of the trimer are hydrogen bonded to residues of the active site of neighboring trimers in the crystal and thus cross-link the molecules in the crystal lattice.