title: Calcium ions promote superoxide dismutase 1 (SOD1) aggregation into non-fibrillar amyloid: a link to toxic effects of calcium overload in amyotrophic lateral sclerosis (ALS)?
abstract: Imbalance in metal ion homeostasis is a hallmark in neurodegenerative conditions involving protein deposition, and amyotrophic lateral sclerosis (ALS) is no exception. In particular, Ca(2+) dysregulation has been shown to correlate with superoxide dismutase-1 (SOD1) aggregation in a cellular model of ALS. Here we present evidence that SOD1 aggregation is enhanced and modulated by Ca(2+). We show that at physiological pH, Ca(2+) induces conformational changes that increase SOD1 β-sheet content, as probed by far UV CD and attenuated total reflectance-FTIR, and enhances SOD1 hydrophobicity, as probed by ANS fluorescence emission. Moreover, dynamic light scattering analysis showed that Ca(2+) boosts the onset of SOD1 aggregation. In agreement, Ca(2+) decreases SOD1 critical concentration and nucleation time during aggregation kinetics, as evidenced by thioflavin T fluorescence emission. Attenuated total reflectance FTIR analysis showed that Ca(2+) induced aggregates consisting preferentially of antiparallel β-sheets, thus suggesting a modulation effect on the aggregation pathway. Transmission electron microscopy and analysis with conformational anti-fibril and anti-oligomer antibodies showed that oligomers and amyloidogenic aggregates constitute the prevalent morphology of Ca(2+)-induced aggregates, thus indicating that Ca(2+) diverts SOD1 aggregation from fibrils toward amorphous aggregates. Interestingly, the same heterogeneity of conformations is found in ALS-derived protein inclusions. We thus hypothesize that transient variations and dysregulation of cellular Ca(2+) levels contribute to the formation of SOD1 aggregates in ALS patients. In this scenario, Ca(2+) may be considered as a pathogenic effector in the formation of ALS proteinaceous inclusions.
authors.affiliation: From the Instituto Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. República 127, 2780-756 Oeiras, Portugal.
authors.forename: Sónia S
authors.initials: SS
authors.lastname: Leal
authors.affiliation: the Molecular Neurobiology Unit, Instituto Biologia Molecular e Celular, 4150-180 Porto, Portugal, and.
authors.forename: Isabel
authors.initials: I
authors.lastname: Cardoso
authors.affiliation: the Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095.
authors.forename: Joan S
authors.initials: JS
authors.lastname: Valentine
authors.affiliation: From the Instituto Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. República 127, 2780-756 Oeiras, Portugal,. Electronic address: gomes@itqb.unl.pt.
authors.forename: Cláudio M
authors.initials: CM
authors.lastname: Gomes
mesh_terms: D000690:Amyotrophic Lateral Sclerosis; D002118:Calcium; D002942:Circular Dichroism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000072105:Superoxide Dismutase-1
chemical_list: D046912:Multiprotein Complexes; C000606290:SOD1 protein, human; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D002118:Calcium
keywords: Amyloid; Amyotrophic Lateral Sclerosis (Lou Gehrig's Disease); Biophysics; Calcium; Circular Dichroism (CD); Electron Microscopy (EM); Infrared Spectroscopy; Neurodegenerative Diseases; Protein Aggregation; Superoxide Dismutase (SOD)