title: 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.
abstract: 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.
authors.affiliation: Chemical Biology Graduate Program, University of Michigan, Ann Arbor, Michigan 48109-2216, USA.
authors.forename: Devayani P
authors.initials: DP
authors.lastname: Bhave
authors.forename: Wen-Ge
authors.initials: WG
authors.lastname: Han
authors.forename: Samuel
authors.initials: S
authors.lastname: Pazicni
authors.forename: James E
authors.initials: JE
authors.lastname: Penner-Hahn
authors.forename: Kate S
authors.initials: KS
authors.lastname: Carroll
authors.forename: Louis
authors.initials: L
authors.lastname: Noodleman
mesh_terms: D018360:Crystallography, X-Ray; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000737:chemistry* / Q000378:metabolism; D011789:Quantum Theory; D055672:Static Electricity; D056928:X-Ray Absorption Spectroscopy
chemical_list: D007506:Iron-Sulfur Proteins; D050862:Oxidoreductases Acting on Sulfur Group Donors; C019618:adenylylsulfate reductase