title: S-SAD, Se-SAD and S/Se-SIRAS using Cu Kalpha radiation: why wait for synchrotron time?
abstract: The structure of Escherichia coli argininosuccinate synthetase (EAS) has been determined using S-SAD, Se-SAD and S/Se-SIRAS data measured with Cu Kalpha radiation. EAS contains 16 methionines and three cysteines in 455 amino acids. At a wavelength of 1.54 A (Cu Kalpha), the native (S-Met) and derivative (Se-Met) proteins yield anomalous signals of approximately 0.86 and 1.6%, respectively. Highly redundant data were measured to 2.0 A from native and derivative EAS crystals. All three structure determinations were carried out in a highly automated manner using SnB and SOLVE/RESOLVE. Despite the minute Bijvoet differences at 1.54 A, the signal was sufficient to determine the heavy-atom substructure and produce high-quality electron-density maps in all three cases. These maps were readily interpretable by the RESOLVE automated building algorithm, which modeled greater than 75% of all three structures. The success of these methods has profound implications for crystallographers experiencing difficulty with heavy-atom incorporation or with limited access to a synchrotron source.
authors.affiliation: Structural Biology and Biochemistry, Research Institute, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, M5G 1X8, Canada.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Lemke
authors.forename: G David
authors.initials: GD
authors.lastname: Smith
authors.forename: P Lynne
authors.initials: PL
authors.lastname: Howell
mesh_terms: D001124:Argininosuccinate Synthase / Q000737:chemistry* / Q000302:isolation & purification; D004926:Escherichia coli / Q000201:enzymology*; D011487:Protein Conformation; D017356:Synchrotrons
chemical_list: D001124:Argininosuccinate Synthase