Density Functional Theory Calculations on the Fe2S2(Arg)(SCys)(SSCys)2 Cluster in HydE: Unique Electronic Structure and Redox Properties
journal contributionposted on 17.01.2011, 00:00 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.