title: Structural consequences of the familial amyotrophic lateral sclerosis SOD1 mutant His46Arg.
abstract: The His46Arg (H46R) mutant of human copper-zinc superoxide dismutase (SOD1) is associated with an unusual, slowly progressing form of familial amyotrophic lateral sclerosis (FALS). Here we describe in detail the crystal structures of pathogenic H46R SOD1 in the Zn-loaded (Zn-H46R) and metal-free (apo-H46R) forms. The Zn-H46R structure demonstrates a novel zinc coordination that involves only three of the usual four liganding residues, His 63, His 80, and Asp 83 together with a water molecule. In addition, the Asp 124 "secondary bridge" between the copper- and zinc-binding sites is disrupted, and the "electrostatic loop" and "zinc loop" elements are largely disordered. The apo-H46R structure exhibits partial disorder in the electrostatic and zinc loop elements in three of the four dimers in the asymmetric unit, while the fourth has ordered loops due to crystal packing interactions. In both structures, nonnative SOD1-SOD1 interactions lead to the formation of higher-order filamentous arrays. The disordered loop elements may increase the likelihood of protein aggregation in vivo, either with other H46R molecules or with other critical cellular components. Importantly, the binding of zinc is not sufficient to prevent the formation of nonnative interactions between pathogenic H46R molecules. The increased tendency to aggregate, even in the presence of Zn, arising from the loss of the secondary bridge is consistent with the observation of an increased abundance of hyaline inclusions in spinal motor neurons and supporting cells in H46R SOD1 transgenic rats.
authors.affiliation: Molecular Biophysics Group, CCLRC Daresbury Laboratory, Warrington, Cheshire, WA4 4AD, UK.
authors.forename: Svetlana
authors.initials: S
authors.lastname: Antonyuk
authors.forename: Jennifer Stine
authors.initials: JS
authors.lastname: Elam
authors.forename: Michael A
authors.initials: MA
authors.lastname: Hough
authors.forename: Richard W
authors.initials: RW
authors.lastname: Strange
authors.forename: Peter A
authors.initials: PA
authors.lastname: Doucette
authors.forename: Jorge A
authors.initials: JA
authors.lastname: Rodriguez
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Hayward
authors.forename: Joan Selverstone
authors.initials: JS
authors.lastname: Valentine
authors.forename: P John
authors.initials: PJ
authors.lastname: Hart
authors.forename: S Samar
authors.initials: SS
authors.lastname: Hasnain
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000201:enzymology* / Q000235:genetics; D001120:Arginine / Q000235:genetics*; D006639:Histidine / Q000235:genetics*; D006801:Humans; D008958:Models, Molecular; D017354:Point Mutation; D011487:Protein Conformation; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000072105:Superoxide Dismutase-1; D015032:Zinc / Q000378:metabolism*
chemical_list: C000606290:SOD1 protein, human; D006639:Histidine; D001120:Arginine; C000606292:Sod1 protein, rat; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D015032:Zinc