Structural Study of Hydrogenase

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The main purpose of this project is to solve the three-dimensional structure of Ni-Fe hydrogenase from one of the sulfate-reducing bacterium by X-ray structure analysis method, and clarify the relationship between the structure and function of it. The structure of the hydrogenase was solved at 3.0 resolution, and has been refined at 1.8 resolution with R-value of 22.9%. The structure reveals an unusual ligands in the Ni-Fe active center. The Fe atom, which was able to be assined in the Ni-Fe center by anoumalous dispersion technique has four non-protein ligands. They have been assigned as three diatomic molecules, and one atom like sulfur. From the stereochemical geometry and atomic parameters of the refined structure, the most probable candidates for the four ligands are S=O,C=N,C=O and one sulfur. The assignment is supported by the data obtained by infrared spectroscopy and pyrolysis-mass spectroscopy. One additional Mg site has been found in the carboxy-terminal region of the large subunit, which is approximately 13 distant from the Ni-Fe active center.