2.3.1.35 crystal structures of Mtb OAT in native form and in its complex with ornithine has been determined at 1.7 and 2.4 A resolutions, respectively. Ornithine binding does not alter the structure of Mtb OAT globally. Its presence stabilizes the three C-terminal residues that are disordered and not observed in the native structure. Stabilization of the C-terminal residues by ornithine reduces the size of the active-site pocket volume in the structure of the ORN complex. The interactions of ORN and the protein residues of Mtb OAT unambiguously delineate the active-site residues of this enzyme in Mtb. 2.3.1.35 crystallization of OAT2 in the presence of N-alpha-acetyl-L-glutamate leads to a structure in which residue T181 is acetylated, the carbonyl oxygen of the acyl-enzyme complex is located in an oxyanion hole and positioned to hydrogen bond with the backbone amide-NH of G112 and the alcohol of T111. Presence of two distinct acyl-enzyme complex structures. The two acyl-enzyme complex structures can interconvert by movement of the T111 side-chain alcohol hydrogen away from the oxyanion hole to hydrogen bond with the backbone carbonyl of the acylated residue, T181 2.3.1.35 crystals grown by either the batch or hanging-drop vapour-diffusion method. The crystals belong to space group P4, with unit-cell parameters a = b = 66.98, c = 427.09 A. The use of the counterdiffusion technique is critical for the production of well ordered crystals 2.3.1.35 crystals of OAT2 in complex with L-Glu are generated. Optimization of crystallization conditions lead to a 2.7 A resolution structure for OAT2 acylated at Thr-181 and in complex with L-Glu (referred to as the acetyl-OAT2-glutamate complex) 2.3.1.35 diffraction to 1.7 A resolution, space group P212121 2.3.1.35 purified recombinant native and selenomethionine-labeled enzymes, hanging drop vapour diffusion method, 12 mg/ml protein in 1.1-1.3 M ammonium sulfate, 0.04 M ammonium phosphate, 0.1 M Tris-HCl, pH 8.0, and 5-8% v/v glycerol, and in case of SeMet-enzyme 5 mM DTT, cryoprotection by 25% glycerol and 2.0 M ammonium sulfate, X-ray diffraction structure determination and analysis at 2.8 A resolution