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apo histidinol-phosphate aminotransferase the internal PLP aldimine adduct and a pyridoxamine 5'-phosphate enzyme complex at resolutions of 2.2 A, 2.1 A and 1.8 A, respectively. The hydrogen bond between the side chain of residue Y21 and the phosphate group of histidinol phosphate is important for recognition of the natural substrate and discrimination against other potential amino donors. Residue N99 does not contribute to the specific recognition of the amino-acid donor. Residues Y123 and Y257 interact with the substrate through van der Waals-interactions
hydrophilic residues in the substrate binding pocket and N-terminal lid allow the entry and binding of its preferential substrate. The pyridoxal phosphate cofactor binds as an internal aldimine via a Schiff ’s base with epsilon-N of Lys232. The inhibitor 2-(N-morpholino)ethanesulfonic acid binds in the active site. The N-terminal lid is restructured upon binding of ligand, leading to a closed conformation of the enzyme necessary for the binding and probable catalysis of the substrate. The closing of the lid upon ligand binding causes Tyr25 to sweep into the active site region and interact with the ligand
wild-type and selenomethionine-labeled enzyme, with or without bound pyridoxal 5'-phosphate or pyridoxamine 5'-phosphate, sitting drop vapour diffusion method, 0.001 ml equal volumes of protein and reservoir solutions, 20°C, 50% v/v ethylene glycol, 5% w/v PEG 1000, sodium acetate, pH 5.1, 2-3 weeks, X-ray diffraction structure determination and analysis at 3.5 A resolution