Complete Loss of Post-translational Modifications Triggers Fibrillar Aggregation of SOD1 in the Familial Form of Amyotrophic Lateral Sclerosis

Laboratory for Structural Neuropathology, Yamanaka Research Unit, RIKEN Brain Science Institute, Wako, Saitama, Japan.
Journal of Biological Chemistry (Impact Factor: 4.57). 07/2008; 283(35):24167-76. DOI: 10.1074/jbc.M802083200
Source: PubMed


Dominant mutations in Cu,Zn-superoxide dismutase (SOD1) cause a familial form of amyotrophic lateral sclerosis (fALS), and aggregation of mutant SOD1 has been proposed to play a role in neurodegeneration. A growing body of evidence suggests that fALS-causing mutations destabilize the native structure of SOD1, leading to aberrant protein interactions for aggregation. SOD1 becomes stabilized and enzymatically active after copper and zinc binding and intramolecular disulfide formation, but it remains unknown which step(s) in the SOD1 maturation process is important in the pathological aggregation. In this study we have shown that apoSOD1 without disulfide is the most facile state for formation of amyloid-like fibrillar aggregates. fALS mutations impair either zinc binding, disulfide formation, or both, leading to accumulation of the aggregation-prone, apo, and disulfide-reduced SOD1. Moreover, we have found that the copper chaperone for SOD1 (CCS) facilitates maturation of SOD1 and that CCS overexpression ameliorates intracellular aggregation of mutant SOD1 in vivo. Based on our in vivo and in vitro results, we propose that facilitation of post-translational modifications is a promising strategy to reduce SOD1 aggregation in the cell.

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    • "Electrophoretic mobility of SOD1/SOD1-EGFP has been shown to increase upon formation of the intramolecular disulfide bond [8] [23]. As shown in Fig. 4 "
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    ABSTRACT: Dominant mutations in Cu,Zn-superoxide dismutase (SOD1) cause a familial form of amyotrophic lateral sclerosis (ALS). A pathological hallmark of the familial ALS is the formation of mutant SOD1 aggregates, leading to the proposal that SOD1 gains toxicities through protein misfolding triggered by mutations. Nevertheless, molecular requirements for mutant SOD1 to acquire pathogenicity still remain obscure. Here, we show that Cys residues in SOD1 are essential to exerting toxicities of SOD1 in a C. elegans model. Exogenous expression of wild-type as well as pathogenic mutant SOD1 fused with a fluorescent protein in C. elegans resulted in the accumulation of disulfide-reduced SOD1 and retarded the worm's motility. In contrast, little effects of exogenously expressed SOD1 on the motility were observed when all four Cys residues in SOD1 were replaced with Ser. Taken together, we propose that deregulation of Cys chemistry in SOD1 proteins is involved in the pathogenesis of SOD1-related ALS. Copyright © 2015. Published by Elsevier Inc.
    Biochemical and Biophysical Research Communications 06/2015; 463(4). DOI:10.1016/j.bbrc.2015.06.084 · 2.30 Impact Factor
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    • "A few ALS patients (10–15%) have mutations in the SOD1 gene; however, misfolding of wild type SOD1 is implicated in the large majority of cases. From these, most SOD1- linked ALS variants are susceptible to unfolding and loss of posttranslational modifications [21] [22]. Indeed, loss of metal ions makes SOD1 aggregation-prone in vitro and in disease models insoluble SOD1 has a very low metallation [23] [24]. "
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    ABSTRACT: Calcium deregulation is a central feature among neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Calcium accumulates in the spinal and brain stem motor neurons of ALS patients triggering multiple pathophysiological processes which have been recently shown to include direct effects on the aggregation cascade of superoxide dismutase 1 (SOD1). SOD1 is a Cu/Zn enzyme whose demetalated form is implicated in ALS protein deposits, contributing to toxic gain of function phenotypes. Here we undertake a combined experimental and computational study aimed at establishing the molecular details underlying the regulatory effects of Ca2 + over SOD1 aggregation potential. Isothermal titration calorimetry indicates entropy driven low affinity association of Ca2 + ions to apo SOD1, at pH 7.5 and 37 °C. Molecular dynamics simulations denote a noticeable loss of native structure upon Ca2 + association that is especially prominent at the zinc-binding and electrostatic loops, whose decoupling is known to expose the central SOD1 β-barrel triggering aggregation. Structural mapping of the preferential apo SOD1 Ca2 + binding locations reveals that among the most frequent ligands for Ca2 + are negatively-charged gatekeeper residues located in boundary positions with respect to segments highly prone to edge-to-edge aggregation. Calcium interactions thus diminish gatekeeping roles of these residues, by shielding repulsive interactions via stacking between aggregating β-sheets, partly blocking fibril formation and promoting amyloidogenic oligomers such as those found in ALS inclusions. Interestingly, many fALS mutations occur at these positions, disclosing how Ca2 + interactions recreate effects similar to those of genetic defects, a finding with relevance to understand sporadic ALS pathomechanisms.
    Biochimica et Biophysica Acta (BBA) - Proteins & Proteomics 11/2014; 1854(2):118-126. DOI:10.1016/j.bbapap.2014.11.005 · 2.75 Impact Factor
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    • "In contrast, SOD1-positive inclusions with ALS-like symptoms were reproduced in a fALS-model mouse expressing human SOD1 with a pathogenic mutation (Turner and Talbot, 2008) and were found to be stained by Thioflavin S, supporting the formation of amyloid-like, β-sheet-rich fibrils in mouse (Wang et al., 2002; Furukawa et al., 2008). Insoluble SOD1 aggregates were also successfully isolated from the spinal cords of affected fALS-model mice, and quite notably, those SOD1 aggregates exhibited seeding activity toward fibrillation of purified SOD1 proteins in vitro. "
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    ABSTRACT: Abnormal accumulation of protein inclusions in motor neurons has been known as a major pathological change in amyotrophic lateral sclerosis (ALS). Increasing numbers of proteins including mutant Cu, Zn-superoxide dismutase (SOD1) have been identified as constituents of pathological inclusions in a form of insoluble fibrillar aggregates. Notably, protein fibrillar aggregates exhibit a self-perpetuating property, which can convert a soluble native protein into insoluble fibrillar aggregates. Such "seeding reaction" of protein fibrils can accelerate the aggregation significantly and would contribute to the spread of inclusion pathologies from an affected cell to its neighboring cells in neurodegenerative diseases. In ALS, a pathological change first occurs at the site of disease onset and then propagates throughout the affected tissues in a time-dependent manner; therefore, it can be assumed that seeded aggregation may be the key factor of disease progression in ALS. In this mini review, we will briefly summarize recent studies on possible roles of a seeded aggregation of SOD1 in pathomechanism of ALS.
    Frontiers in Cellular Neuroscience 03/2014; 8:83. DOI:10.3389/fncel.2014.00083 · 4.29 Impact Factor
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