title: Structure of viscotoxin A3: disulfide location from weak SAD data.
abstract: The crystal structure of viscotoxin A3 (VT A3) extracted from European mistletoe (Viscum album L.) has been solved using the anomalous diffraction of the native S atoms measured in-house with Cu Kalpha radiation to a resolution of 2.2 A and truncated to 2.5 A. A 1.75 A resolution synchrotron data set was used for phase expansion and refinement. An innovation in the dual-space substructure-solution program SHELXD enabled the individual S atoms of the disulfide bonds to be located using the Cu Kalpha data; this resulted in a marked improvement in the phasing compared with the use of super-S atoms. The VT A3 monomer consists of 46 amino acids with three disulfide bridges and has an overall fold resembling the canonical architecture of the alpha- and beta-thionins, a capital letter L. The asymmetric unit consists of two monomers related by a local twofold axis and held together by hydrophobic interactions between the monomer units. One phosphate anion (confirmed by 31P-NMR and MS) is associated with each monomer.
authors.affiliation: Lehrstuhl für Strukturchemie, Georg-August Universität, Tammannstrasse 4, Göttingen, Germany.
authors.forename: Judit E
authors.initials: JE
authors.lastname: Debreczeni
authors.forename: Beatrix
authors.initials: B
authors.lastname: Girmann
authors.forename: Axel
authors.initials: A
authors.lastname: Zeeck
authors.forename: Ralph
authors.initials: R
authors.lastname: Krätzner
authors.forename: George M
authors.initials: GM
authors.lastname: Sheldrick
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray / Q000379:methods; D004220:Disulfides / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010710:Phosphates / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D055672:Static Electricity; D017356:Synchrotrons; D028182:Viscum album / Q000737:chemistry
chemical_list: D004220:Disulfides; D010710:Phosphates; D010940:Plant Proteins; C485281:viscotoxin A3, Viscum album; C488038:viscotoxin