2.1.1.235 enzyme in complex with S-adenosyl-L-homocysteine and dTDP-3-N-methylamino-3,6-dideoxyglucose., X-ray diffraction structure determination and analysis at 1.6 A resolution 735676 2.1.1.235 hanging drop method of vapor diffusion method, high resolution X-ray structures of TylM1, one in which the enzyme contains bound SAM and dTDP-phenol and the second in which the protein is complexed with S-adenosyl-L-homocysteine and dTDP-3-amino-3,6-dideoxyglucose, its natural substrate. Combined, these two structures, solved to 1.35 A and 1.79 A resolution, respectively, show the orientations of SAM and the dTDP-linked sugar substrate within the active site region. Specifically, the C-30 amino group of the hexose is in the correct position for an in-line attack at the reactive methyl group of S-adenosyl-L-methionine. High-resolution X-ray models show that the observed perturbations in the kinetic constants of the mutant enzynes H123A and H123N are not due to major changes in their threedimensional folds. Most likely the proton on the C-3' amino group is transferred to one of the water molecules lining the active site pocket as catalysis proceeds 714271 2.1.1.235 purified enzyme TylM1 mutants Y14F, Y14pAF, and S120A in complex with SAH and dTDP-phenol, X-ray diffraction structure determination and analysis at 1.37-1.78 A resolution 756061