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Density Functional Theory Calculations on the Fe2S2(Arg)(SCys)(SSCys)2 Cluster in HydE: Unique Electronic Structure and Redox Properties

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journal contribution
posted on 17.01.2011, 00:00 authored by Abhishek Dey
A Fe2S2 cluster with unprecedented CysSS (cysteinepersulfide) coordination has been observed crystallographically in the AdoMet-dependent hydrogenase maturase enzyme HydE. Geometry-optimized density functional theory calculations are used to develop an electronic structure description of this unusual cluster. The results indicate that the CysSS ligand is unique because it can act as a donor as well as an acceptor ligand. This is due to the presence of S−S π* (occupied) and S−S σ* (unoccupied) orbitals in this ligand. Extensive back-bonding is observed between the cluster and the S−S σ* orbital. The back-bonding is significantly higher in the reduced state, which is calculated to shift the reduction potential of this Fe2S2 cluster by +400 mV in the gas phase relative to a CysS-coordinated Fe2S2 cluster model of BioB.