Geometric and electrostatic study of the [4Fe-4S] cluster of adenosine-5′-phosphosulfate reductase from broken symmetry density functional calculations and extended X-ray absorption fine structure spectroscopy.
Adenosine-5′-phosphosulfate reductase (APSR) is an iron-sulfur protein that catalyzes the reduction of adenosine-5′-phosphosulfate (APS) to sulfite. APSR coordinates to a [4Fe-4S] cluster via a conserved CC-X ∼80-CXXC motif, and the cluster is essential for catalysis. Despite extensive functional, structural, and spectroscopic studies, the exact role of the iron-sulfur cluster in APS reduction remains unknown. To gain an understanding into the role of the cluster, density functional theory (DFT) analysis and extended X-ray fine structure spectroscopy (EXAFS) have been performed to reveal insights into the coordination, geometry, and electrostatics of the [4Fe-4S] cluster. X-ray absorption near-edge structure (XANES) data confirms that the cluster is in the [4Fe-4S]2+ state in both native and substrate-bound APSR while EXAFS data recorded at ∼0.1 Å resolution indicates that there is no significant change in the structure of the [4Fe-4S] cluster between the native and substrate-bound forms of the protein. On the other hand, DFT calculations provide an insight into the subtle differences between the geometry of the cluster in the native and APS-bound forms of APSR. A comparison between models with and without the tandem cysteine pair coordination of the cluster suggests a role for the unique coordination in facilitating a compact geometric structure and "fine-tuning" the electronic structure to prevent reduction of the cluster. Further, calculations using models in which residue Lys144 is mutated to Ala confirm the finding that Lys144 serves as a crucial link in the interactions involving the [4Fe-4S] cluster and APS.
American Chemical Society
Digital Object Identifier (DOI)
Bhave, D.P., Han, W.-G., Pazicni, S., Penner-Hahn, J.E., Carroll, K.S., Noodleman, L. Geometric and electrostatic study of the [4Fe-4S] cluster of adenosine-5′-phosphosulfate reductase from broken symmetry density functional calculations and extended X-ray absorption fine structure spectroscopy. (2011) Inorganic Chemistry, 50 (14), pp. 6610-6625. doi: 10.1021/ic200446c
© 2011 American Chemical Society