Crystallographic and FTIR Spectroscopic Evidence of Changes in Fe Coordination Upon Reduction of the Active Site of the Fe-Only Hydrogenase fromDesulfovibriodesulfuricans

Abstract

Fe-only hydrogenases, as well as their NiFe counterparts, display unusual intrinsic high-frequency IR bands that have been assigned to CO and CN(-) ligation to iron in their active sites. FTIR experiments performed on the Fe-only hydrogenase from Desulfovibrio desulfuricans indicate that upon reduction of the active oxidized form, there is a major shift of one of these bands that is provoked, most likely, by the change of a CO ligand from a bridging position to a terminal one. Indeed, the crystal structure of the reduced active site of this enzyme shows that the previously bridging CO is now terminally bound to the iron ion that most likely corresponds to the primary hydrogen binding site (Fe2). The CO binding change may result from changes in the coordination sphere of Fe2 or its reduction. Superposition of this reduced active site with the equivalent region of a NiFe hydrogenase shows a remarkable coincidence between the coordination of Fe2 and that of the Fe ion in the NiFe cluster. Both stereochemical and mechanistic considerations suggest that the small organic molecule found at the Fe-only hydrogenase active site and previously modeled as 1,3-propanedithiolate may, in fact, be di-(thiomethyl)-amine.

The role of the maturase HydG in [FeFe]‐hydrogenase active site synthesis and assembly

“…X-ray crystallography and FTIR spectroscopy have shown that the three enzymes are characterized by complex active sites that have in common a Fe(CO) x unit, and, in the case of [NiFe]-and [FeFe]-hydrogenases, two CN À ligands ( Fig. 1) [5][6][7][8][9]. However, the [NiFe]-and [FeFe]-hydrogenases do not use the same molecular strategy to link the two metal ions of the dinuclear site: whereas two protein-bound cysteines provide the two sulfur bridges in [NiFe]-hydrogenases, this bridge in [FeFe]-hydrogenases is provided by a non-protein dithiolate ligand, whose composition has not been determined experimentally but was proposed, on the basis of X-ray crystallographic data, to be À SCH 2 XCH 2 S À , with X being either nitrogen, oxygen or carbon [10].…”

“…However, the [NiFe]-and [FeFe]-hydrogenases do not use the same molecular strategy to link the two metal ions of the dinuclear site: whereas two protein-bound cysteines provide the two sulfur bridges in [NiFe]-hydrogenases, this bridge in [FeFe]-hydrogenases is provided by a non-protein dithiolate ligand, whose composition has not been determined experimentally but was proposed, on the basis of X-ray crystallographic data, to be À SCH 2 XCH 2 S À , with X being either nitrogen, oxygen or carbon [10]. Because of the potential role of an amine group in proton trafficking, we consider the first hypothesis as the most likely [9].…”

Unsaturated, Mixed‐Valence Diiron Dithiolate Model for the Hox State of the [FeFe] Hydrogenase

“…In general, the [Fe 2 (SR) 2 L 6 ] framework approaches that proposed for the H ox state of the active site. [2,9] Of specific interest, the oxidation has caused the {Fe(CO)(dppv)} center to rotate about the Fe-Fe axis. The apical site on the {Fe(dppv)} center is vacant, and the [BF 4 ] − anion is approximately 5 Å away from this "distal" Fe center.…”

Studies on the Condensation Pathway to and Properties of Diiron Azadithiolate Carbonyls

“…1-5 These efforts are motivated by the following considerations: (i) the possibility that the azadithiolate is the dithiolate cofactor in the Fe-only hydrogenases, 6 (ii) the possibility that such a ligand could play a functional role in the heterolytic activation of H 2 ,7,8 and (iii) the amine is a versatile point of attachment for diverse substituents. 4,5 The functionalization of organometallic sulfides is an active area.…”

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AbstractReaction of Fe 2 (SH) 2 (CO) 6 and HCHO, which gives Fe 2 [(SCH 2 ) 2 NH](CO) 6 in the presence of NH 3

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