The Mössbauer Parameters of the Proximal Cluster of Membrane-Bound Hydrogenase Revisited: A Density Functional Theory Study

Abstract

An unprecedented [4Fe-3S] cluster proximal to the regular [NiFe] active site has recently been found to be responsible for the ability of membrane-bound hydrogenases (MBHs) to oxidize dihydrogen in the presence of ambient levels of oxygen. Starting from proximal cluster models of a recent DFT study on the redox-dependent structural transformation of the [4Fe-3S] cluster, 57Fe Mössbauer parameters (electric field gradients, isomer shifts, and nuclear hyperfine couplings) were calculated using DFT. Our results revise the previously reported correspondence of Mössbauer signals and iron centers in the [4Fe-3S]3+ reduced-state proximal cluster. Similar conflicting assignments are also resolved for the [4Fe-3S]5+ superoxidized state with particular regard to spin-coupling in the broken-symmetry DFT calculations. Calculated 57Fe hyperfine coupling (HFC) tensors expose discrepancies in the experimental set of HFC tensors and substantiate the need for additional experimental work on the magnetic properties of the MBH proximal cluster in its reduced and superoxidized redox states.

Successes, challenges, and opportunities for quantum chemistry in understanding metalloenzymes for solar fuels research

“…The calculated isomer shifts and quadrupole splitting helped in discriminating between different interpretation of the data and a clear assignment of both the spin coupling scheme and the redox states within the iron-sulphur cluster was made possible. 273 Combined with theoretical calculations, this spectroscopic technique has been also employed to study diverse [FeFe] hydrogenase intermediates. The putative structures of these intermediates were obtained from QM/MM calculations and the comparison between calculated and experimental isomer shifts could be used to discriminate between different intermediates following a proper calibration based on iron-based model systems.…”

Electronic landscape of the P-cluster of nitrogenase as revealed through many-electron quantum wavefunction simulations

“…In both the S = 1/2 and S = 5/2 ground-states, the charge is localized, with oxidation mainly on Fe4, which coordinates to the oxygen in Ser-188 in conjunction with the structural opening. Additionally, the irons in the right cubane are overall more reduced than the hydrogenases (30)(31)(32)(33). Unlike in the P N cluster, there is no simple classical picture of the spincoupling in P OX ; each state is spin-canted (34) and involves a linear combination of multiple spin coupling schemes.…”

“…4c, 4d). The opening of the left cubane resembles that seen in isolated cubanes under oxidation, such as the conforma-tional change of the [Fe 4 S 3 ] cluster upon oxidation in oxygen-tolerant membrane-bound [NiFe] hydrogenases (30)(31)(32)(33). Unlike in the P N cluster, there is no simple classical picture of the spincoupling in P OX ; each state is spin-canted (34) and involves a linear combination of multiple spin coupling schemes.…”

Mutation effects on charge transport through the p58c iron–sulfur protein

“…The other layer is a ferric pair with formal charge +3 on each ion and S 2 ¼ 4. [20][21][22] A 2D NMR study of the high potential iron-sulfur protein from Chromatium vinosum assigned the rst two Cys ligands in the sequence (Cys 43 and Cys 46) to the more oxidized layer and the other two Cys ligands (Cys 61 and Cys 75) to the less oxidized layer. 23 However, this assignment cannot be generalized to other iron-sulfur proteins.…”