title: Evidence for the formation of disulfide radicals in protein crystals upon X-ray irradiation.
abstract: Irradiation of proteins with intense X-ray radiation produced by third-generation synchrotron sources generates specific structural and chemical alterations, including breakage of disulfide bonds and decarboxylation. In this paper, disulfide bond lengths in irradiated crystals of the enzyme Torpedo californica acetylcholinesterase are examined based on quantum simulations and on experimental data published previously. The experimental data suggest that one disulfide bond elongates by approximately 0.7 A upon X-ray irradiation as seen in a series of nine data sets collected on a single crystal. Simulation of the same bond suggests elongation by a similar value if a disulfide-radical anion is formed by trapping an electron. The absorption spectrum of a crystal irradiated under similar conditions shows a peak at approximately 400 nm, which in aqueous solution has been attributed to disulfide radicals. The results suggest that the formation of disulfide radicals in protein crystals owing to X-ray irradiation can be observed experimentally, both by structural means and by absorption spectroscopy.
authors.affiliation: Institut de Biologie Structurale, Laboratoire de Biophysique Moléculaire, 38027 Grenoble, France. weik@ibs.fr
authors.forename: Martin
authors.initials: M
authors.lastname: Weik
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Bergès
authors.forename: Maria L
authors.initials: ML
authors.lastname: Raves
authors.forename: Piet
authors.initials: P
authors.lastname: Gros
authors.forename: Sean
authors.initials: S
authors.lastname: McSweeney
authors.forename: Israel
authors.initials: I
authors.lastname: Silman
authors.forename: Joel L
authors.initials: JL
authors.lastname: Sussman
authors.forename: Chantal
authors.initials: C
authors.lastname: Houée-Levin
authors.forename: Raimond B G
authors.initials: RB
authors.lastname: Ravelli
mesh_terms: D003460:Crystallization; D004220:Disulfides / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D004583:Electrons; D005609:Free Radicals / Q000528:radiation effects; D006801:Humans; D008958:Models, Molecular; D011487:Protein Conformation / Q000528:radiation effects*; D011506:Proteins / Q000737:chemistry / Q000528:radiation effects*; D014961:X-Ray Diffraction
chemical_list: D004220:Disulfides; D005609:Free Radicals; D011506:Proteins