title: In-house SAD phasing with surface-bound cerium ions.
abstract: The anomalous signal of cerium(III) ions present in a derivative of hen egg-white lysozyme (HEWL) crystals obtained by the addition of 0.025 M cerium chloride to the crystallization medium was used for phasing. X-ray intensity data were collected to 2 Å resolution using an in-house Cu Kα radiation data-collection facility. Phasing of a single-wavelength data set purely based on its f'' led to a clearly interpretable electron-density map. Automated substructure solution by AutoSol in PHENIX resulted in four highest peaks corresponding to cerium(III) ions with data limited to 3 Å resolution, and about 90% of the residues were built automatically by AutoBuild in PHENIX. Cerium(III) ions bound on the surface of the enzyme are found to interact mainly with the main-chain and side-chain carbonyl groups of Asn, Glu, Tyr and Asp and with water molecules. Ce(3+) ions were used as potential anomalous scatterers for the in-house single-wavelength anomalous scattering technique, and this is proposed as a tool for macromolecular phasing and for the study of the interactions of trivalent metal ions with proteins and other macromolecules.
authors.affiliation: CAS in Crystallography and Biophysics, University of Madras, Maraimalai (Guindy) Campus, Chennai, Tamilnadu, India.
authors.forename: K Natesan
authors.initials: KN
authors.lastname: Vennila
authors.forename: Devadasan
authors.initials: D
authors.lastname: Velmurugan
mesh_terms: D002412:Cations / Q000737:chemistry; D002563:Cerium / Q000737:chemistry*; D018360:Crystallography, X-Ray / Q000379:methods*; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000032:analysis* / Q000737:chemistry; D013499:Surface Properties
chemical_list: D002412:Cations; D011506:Proteins; D002563:Cerium