1cc1
From Proteopedia
|
CRYSTAL STRUCTURE OF A REDUCED, ACTIVE FORM OF THE NI-FE-SE HYDROGENASE FROM DESULFOMICROBIUM BACULATUM
Overview
BACKGROUND: [NiFeSe] hydrogenases are metalloenzymes that catalyze the, reaction H2<-->2H+ + 2e-. They are generally heterodimeric, contain three, iron-sulfur clusters in their small subunit and a nickel-iron-containing, active site in their large subunit that includes a selenocysteine (SeCys), ligand. RESULTS: We report here the X-ray structure at 2.15 A resolution, of the periplasmic [NiFeSe] hydrogenase from Desulfomicrobium baculatum in, its reduced, active form. A comparison of active sites of the oxidized, as-prepared, Desulfovibrio gigas and the reduced D. baculatum hydrogenases, shows that in the reduced enzyme the nickel-iron distance is 0.4 A shorter, than in the oxidized enzyme. In addition, the putative oxo ligand, detected in the as-prepared D. gigas enzyme, is absent from the D., baculatum hydrogenase. We also observe higher-than-average temperature, factors for both the active site nickel-selenocysteine ligand and the, neighboring Glu18 residue, suggesting that both these moieties are, involved in proton transfer between the active site and the molecular, surface. Other differences between [NiFeSe] and [NiFe] hydrogenases are, the presence of a third [4Fe4S] cluster replacing the [3Fe4S] cluster, found in the D. gigas enzyme, and a putative iron center that substitutes, the magnesium ion that has already been described at the C terminus of the, large subunit of two [NiFe] hydrogenases. CONCLUSIONS: The heterolytic, cleavage of molecular hydrogen seems to be mediated by the nickel center, and the selenocysteine residue. Beside modifying the catalytic properties, of the enzyme, the selenium ligand might protect the nickel atom from, oxidation. We conclude that the putative oxo ligand is a signature of, inactive 'unready' [NiFe] hydrogenases.
About this Structure
1CC1 is a Protein complex structure of sequences from Desulfomicrobium baculatum with NI, FE2, SF4, FCO and H2S as ligands. Active as Ferredoxin hydrogenase, with EC number 1.12.7.2 Full crystallographic information is available from OCA.
Reference
The crystal structure of a reduced [NiFeSe] hydrogenase provides an image of the activated catalytic center., Garcin E, Vernede X, Hatchikian EC, Volbeda A, Frey M, Fontecilla-Camps JC, Structure. 1999 May;7(5):557-66. PMID:10378275
Page seeded by OCA on Tue Nov 20 12:19:54 2007
