title: Phasing power at the K absorption edge of organic arsenic.
abstract: Single/multiple-wavelength anomalous dispersion (SAD/MAD) experiments were performed on a crystal of an organic arsenic derivative of hen egg-white lysozyme. A para-arsanilate compound used as a crystallizing reagent was incorporated into the ordered solvent region of the lysozyme molecule. Diffraction data were collected to high resolution (</=2.0 A) at three wavelengths around the K edge (1.04 A) of arsenic at beamline BM30A, ESRF synchrotron. Anomalous Patterson maps clearly showed the main arsanilate site to be between three symmetry-related lysozyme molecules, at a location previously occupied by a para-toluenesulfonate anion. MAD phases at 2 A derived using the program SHARP led to an electron-density map of sufficient quality to start manual building of the protein model. Amplitudes from a second crystal measured to a resolution of 1.8 A at the peak wavelength revealed two additional heavy-atom sites, which reinforced the anomalous subset model and therefore dramatically improved the phasing power of the arsenic derivative. The subsequent solvent-flattened map was of such high accuracy that the program ARP/wARP was able to build a nearly complete model automatically. This work emphasizes the great potential of arsenic for de novo structure determination using anomalous dispersion methods.
authors.affiliation: Laboratoire LURE, Centre Universitaire Paris-Sud, Bâtiment 209D, BP 34, 91898 Orsay CEDEX, France. retailleau@lure.u-psud.fr
authors.forename: Pascal
authors.initials: P
authors.lastname: Retailleau
authors.forename: Thierry
authors.initials: T
authors.lastname: Prangé
mesh_terms: D000818:Animals; D001151:Arsenic / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D002645:Chickens; D003460:Crystallization / Q000379:methods; D003461:Crystallography; D018360:Crystallography, X-Ray / Q000379:methods*; D004527:Egg Proteins / Q000737:chemistry / Q000378:metabolism; D009113:Muramidase / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D012984:Software; D013050:Spectrometry, Fluorescence; D055672:Static Electricity; D017356:Synchrotrons
chemical_list: D004527:Egg Proteins; C421864:hen egg lysozyme; D009113:Muramidase; D001151:Arsenic