title: Azurin as a protein scaffold for a low-coordinate nonheme iron site with a small-molecule binding pocket.
abstract: The apoprotein of Pseudomonas aeruginosa azurin binds iron(II) to give a 1:1 complex, which has been characterized by electronic absorption, Mössbauer, and NMR spectroscopies, as well as X-ray crystallography and quantum-chemical computations. Despite potential competition by water and other coordinating residues, iron(II) binds tightly to the low-coordinate site. The iron(II) complex does not react with chemical redox agents to undergo oxidation or reduction. Spectroscopically calibrated quantum-chemical computations show that the complex has high-spin iron(II) in a pseudotetrahedral coordination environment, which features interactions with side chains of two histidines and a cysteine as well as the C═O of Gly45. In the (5)A(1) ground state, the d(z(2)) orbital is doubly occupied. Mutation of Met121 to Ala leaves the metal site in a similar environment but creates a pocket for reversible binding of small anions to the iron(II) center. Specifically, azide forms a high-spin iron(II) complex and cyanide forms a low-spin iron(II) complex.
authors.affiliation: Department of Chemistry, University of Rochester, Rochester, New York 14618, United States.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: McLaughlin
authors.forename: Marius
authors.initials: M
authors.lastname: Retegan
authors.forename: Eckhard
authors.initials: E
authors.lastname: Bill
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Payne
authors.forename: Hannah S
authors.initials: HS
authors.lastname: Shafaat
authors.forename: Salvador
authors.initials: S
authors.lastname: Peña
authors.forename: Jawahar
authors.initials: J
authors.lastname: Sudhamsu
authors.forename: Amy A
authors.initials: AA
authors.lastname: Ensign
authors.forename: Brian R
authors.initials: BR
authors.lastname: Crane
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.forename: Patrick L
authors.initials: PL
authors.lastname: Holland
mesh_terms: D001386:Azides / Q000737:chemistry; D001400:Azurin / Q000737:chemistry*; D001665:Binding Sites; D056831:Coordination Complexes / Q000737:chemistry; D018360:Crystallography, X-Ray; D003486:Cyanides / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D019159:Nonheme Iron Proteins / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory
chemical_list: D001386:Azides; D056831:Coordination Complexes; D003486:Cyanides; D019159:Nonheme Iron Proteins; D001400:Azurin; D007501:Iron