The 2.0 Å Crystal Structure of Cyanide Metmyoglobin Reconstituted with 5,10,15,20-Tetrapropylhemin

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Abstract
Sperm whale metmyoglobin reconstituted with 5,10,15,20-tetrapropylhemin was crystallized in the space group P212121, which was different from the space group P21 of the native. The crystal structure of the reconstituted metmyoglobin was determined by the molecular replacement method. The atomic coordinates were refined to R=0.209 at 2.0 Å resolution. The overall structure is essentially the same as that of the native. The pronounced structural change is observed in the side-chain orientation of Arg 45 moving to the surface of the molecule. This conformational change may reflect a side-chain fluctuation that allows the small ligands to approach the heme pocket from the outside of the protein. The porphyrin ring does not rotate freely about the Fe–Nε (His 93) bond in the crystalline state, although temperature-dependent NMR spectra suggest its free rotation in solution.