title: Use of complementary cation and anion heavy-atom salt derivatives to solve the structure of cytochrome P450 46A1.
abstract: Human cytochrome P450 46A1 (CYP46A1) is one of the key enzymes in cholesterol homeostasis in the brain. The crystallization and heavy-atom structure solution of an active truncated CYP46A1 in complex with the high-affinity substrate analogue cholesterol-3-sulfate (CH-3S) is reported. The 2.6 angstroms structure of CYP46A1-CH-3S was solved using both anion and cation heavy-atom salts. In addition to the native anomalous signal from the haem iron, an NaI anion halide salt derivative and a complementary CsCl alkali-metal cation salt derivative were used. The general implications of the use of halide and alkali-metal quick soaks are discussed. The importance of using isoionic strength buffers, the titration of heavy-atom salts into different ionic species and the role of concentration are considered. It was observed that cation/anion-binding sites will occasionally overlap, which could negatively impact upon mixed RbBr soaks used for multiple anomalous scatterer MAD (MMAD). The use of complementary cation and anion heavy-atom salt derivatives is a convenient and powerful tool for MIR(AS) structure solution.
authors.affiliation: Sealy Center for Structural and Molecular Biophysics, UTMB Galveston, TX 77555, USA. white@xray.utmb.edu
authors.forename: Mark Andrew
authors.initials: MA
authors.lastname: White
authors.forename: Natalia
authors.initials: N
authors.lastname: Mast
authors.forename: Ingemar
authors.initials: I
authors.lastname: Bjorkhem
authors.forename: Eric F
authors.initials: EF
authors.lastname: Johnson
authors.forename: C David
authors.initials: CD
authors.lastname: Stout
authors.forename: Irina A
authors.initials: IA
authors.lastname: Pikuleva
mesh_terms: D000838:Anions / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D018360:Crystallography, X-Ray / Q000379:methods; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D008958:Models, Molecular
chemical_list: D000838:Anions; D002412:Cations; D003577:Cytochrome P-450 Enzyme System