ALS-causing SOD1 mutations promote production of copper-deficient misfolded species

Point mutations scattered throughout the sequence of Cu,Zn superoxide dismutase (SOD1) cause a subset of amyotrophic lateral sclerosis (ALS) cases. SOD1 is a homodimer in which each subunit binds one copper atom and one zinc atom. Inclusions containing misfolded SOD1 are seen in motor neurons of SOD1-associated ALS cases. The mechanism by which these diverse mutations cause misfolding and converge on the same disease is still not well understood. Previously, we developed several time-resolved techniques to monitor structural changes in SOD1 as it unfolds in guanidine hydrochloride. By measuring the rates of Cu and Zn release using an absorbance-based assay, dimer dissociation through chemical cross-linking, and β-barrel conformation changes by tryptophan fluorescence, we established that wild-type SOD1 unfolds by a branched pathway involving a Zn-deficient monomer as the dominant intermediate of the major pathway, and with various metal-loaded and Cu-deficient dimers populated along the minor pathway. We have now compared the unfolding pathway of wild-type SOD1 with those of A4V, G37R, G85R, G93A, and I113T ALS-associated mutant SOD1. The kinetics of unfolding of the mutants were generally much faster than those of wild type. However, all of the mutants utilize the minority pathway to a greater extent than the wild-type protein, leading to greater populations of Cu-deficient intermediates and decreases in Zn-deficient intermediates relative to the wild-type protein. The greater propensity of the mutants to populate Cu-deficient states potentially implicates these species as a pathogenic form of SOD1 in SOD1-associated ALS and provides a novel target for therapeutic intervention.     

Structural and thermodynamic effects of post-translational modifications in mutant and wild type Cu, Zn superoxide dismutase

Aggregation of Cu,Zn superoxide dismutase (SOD1) is implicated in amyotrophic lateral sclerosis. Glutathionylation and phosphorylation of SOD1 is omnipresent in the human body, even in healthy individuals, and has been shown to increase SOD1 dimer dissociation, which is the first step on the pathway toward SOD1 aggregation. We found that post-translational modification of SOD1, especially glutathionylation, promotes dimer dissociation. We discovered an intermediate state in the pathway to dissociation, a conformational change that involves a “loosening” of the β-barrels and a loss or shift of dimer interface interactions. In modified SOD1, this intermediate state is stabilized as compared to unmodified SOD1. The presence of post-translational modifications could explain the environmental factors involved in the speed of disease progression. Because post-translational modifications such as glutathionylation are often induced by oxidative stress, post-translational modification of SOD1 could be a factor in the occurrence of sporadic cases of amyotrophic lateral sclerosis, which represent 90% of all cases of the disease.     

Familial amyotrophic lateral sclerosis-associated mutations decrease the thermal stability of distinctly metallated species of human copper/zinc superoxide dismutase

We report the thermal stability of wild type (WT) and 14 different variants of human copper/zinc superoxide dismutase (SOD1) associated with familial amyotrophic lateral sclerosis (FALS). Multiple endothermic unfolding transitions were observed by differential scanning calorimetry for partially metallated SOD1 enzymes isolated from a baculovirus system. We correlated the metal ion contents of SOD1 variants with the occurrence of distinct melting transitions. Altered thermal stability upon reduction of copper with dithionite identified transitions resulting from the unfolding of copper-containing SOD1 species. We demonstrated that copper or zinc binding to a subset of "WT-like" FALS mutants (A4V, L38V, G41S, G72S, D76Y, D90A, G93A, and E133Delta) conferred a similar degree of incremental stabilization as did metal ion binding to WT SOD1. However, these mutants were all destabilized by approximately 1-6 degrees C compared with the corresponding WT SOD1 species. Most of the "metal binding region" FALS mutants (H46R, G85R, D124V, D125H, and S134N) exhibited transitions that probably resulted from unfolding of metal-free species at approximately 4-12 degrees C below the observed melting of the least stable WT species. We conclude that decreased conformational stability shared by all of these mutant SOD1s may contribute to SOD1 toxicity in FALS.     

Zinc binding modulates the entire folding free energy surface of human Cu,Zn superoxide dismutase

Over 100 amino acid replacements in human Cu,Zn superoxide dismutase (SOD) are known to cause amyotrophic lateral sclerosis, a gain-of-function neurodegenerative disease that destroys motor neurons. Supposing that aggregates of partially folded states are primarily responsible for toxicity, we determined the role of the structurally important zinc ion in defining the folding free energy surface of dimeric SOD by comparing the thermodynamic and kinetic folding properties of the zinc-free and zinc-bound forms of the protein. The presence of zinc was found to decrease the free energies of a peptide model of the unfolded monomer, a stable variant of the folded monomeric intermediate, and the folded dimeric species. The unfolded state binds zinc weakly with a micromolar dissociation constant, and the folded monomeric intermediate and the native dimeric form both bind zinc tightly, with subnanomolar dissociation constants. Coupled with the strong driving force for the subunit association reaction, the shift in the populations toward more well-folded states in the presence of zinc decreases the steady-state populations of higher-energy states in SOD under expected in vivo zinc concentrations (approximately nanomolar). The significant decrease in the population of partially folded states is expected to diminish their potential for aggregation and account for the known protective effect of zinc. The ∼ 100-fold increase in the rate of folding of SOD in the presence of micromolar concentrations of zinc demonstrates a significant role for a preorganized zinc-binding loop in the transition-state ensemble for the rate-limiting monomer folding reaction in this β-barrel protein.     

Mapping the folding free energy surface for metal-free human Cu,Zn superoxide dismutase

Mutations at many different sites in the gene encoding human Cu,Zn superoxide dismutase (SOD) are known to be causative agents in amyotrophic lateral sclerosis (ALS). One explanation for the molecular basis of this pathology is the aggregation of marginally soluble, partially structured states whose populations are enhanced in the protein variants. As a benchmark for testing this hypothesis, the equilibrium and kinetic properties of the reversible folding reaction of a metal-free variant of SOD were investigated. Reversibility was achieved by replacing the two non-essential cysteine residues with non-oxidizable analogs, C6A/C111S, to produce apo-AS-SOD. The metal-free pseudo-wild-type protein is folded and dimeric in the absence of chemical denaturants, and its equilibrium folding behavior is well described by an apparent two-state mechanism involving the unfolded monomer and the native dimer. The apparent free energy of folding in the absence of denaturant and at standard state is -20.37(+/- 1.04) kcal (mol dimer)(-1). A global analysis of circular dichroism kinetic traces for both unfolding and refolding reactions, combined with results from small angle X-ray scattering and time-resolved fluorescence anisotropy measurements, supports a sequential mechanism involving the unfolded monomer, a folded monomeric intermediate, and the native dimer. The rate-limiting monomer folding reaction is followed by a near diffusion-limited self-association reaction to form the native dimer. The relative population of the folded monomeric intermediate is predicted not to exceed 0.5% at micromolar concentrations of protein under equilibrium and both strongly unfolding and refolding conditions for metal-free pseudo-wild-type SOD.     

Solvent sensitivity of protein aggregation in Cu,Zn superoxide dismutase: a molecular dynamics simulation study

Misfolding and aggregation of Cu, Zn Superoxide Dismutase (SOD1) is often found in amyotrophic lateral sclerosis (ALS) patients. The central apo SOD1 barrel was involved in protein maturation and pathological aggregation in ALS. In this work, we employed atomistic molecular dynamics (MD) simulations to study the conformational dynamics of SOD1^barrel monomer in different concentrations of trifluoroethanol (TFE). We find concentration dependence unusual structural and dynamical features, characterized by the local unfolding of SOD1^barrel. This partially unfolded structure is characterized by the exposure of hydrophobic core, is highly dynamic in nature, and is the precursor of aggregation seen in SOD1^barrel. Our computational studies supports the hypothesis of the formation of aggregation ‘building blocks’ by means of local unfolding of apo monomer as the mechanism of SOD1 fibrillar aggregation. The non-monotonic TFE concentration dependence of protein conformational changes was explored through simulation studies. Our results suggest that altered protein conformation and dynamics within its structure may underlie the aggregation of SOD1 in ALS.     

肌萎缩性侧索硬化症相关的Cu,Zn-SOD

超氧化物歧化酶（superoxide dismutase,SOD）被称为生物体内自由基的清洁剂,其主要形式Cu,Zn-SOD称SOD1. SOD1突变体可引起致死性运动神经元疾病肌萎缩性侧索硬化症(ALS).但是,SOD1的毒性机理尚未完全清楚.本文概述了SOD1、Cu分子伴侣（copper chaperone for SOD1,CCS）的分子结构和CCS活化SOD1的机理,重点分析了突变体SOD1构象变化的原因及其在ALS中的可能致病机制的最新研究进展.     

Crystal structure of the second domain of the human copper chaperone for superoxide dismutase

The human copper chaperone for superoxide dismutase (hCCS) delivers the essential copper ion cofactor to copper,zinc superoxide dismutase (SOD1), a key enzyme in antioxidant defense. Mutations in SOD1 are linked to familial amyotrophic lateral sclerosis (FALS), a fatal neurodegenerative disorder. The molecular mechanisms by which SOD1 is recognized and activated by hCCS are not understood. To better understand this biochemical pathway, we have determined the X-ray structure of the largest domain of hCCS (hCCS Domain II) to 2. 75 A resolution. The overall structure is closely related to that of its target enzyme SOD1, consisting of an eight-stranded beta-barrel and a zinc-binding site formed by two extended loops. The first of these loops provides the ligands to a bound zinc ion, and is analogous to the zinc subloop in SOD1. The second structurally resembles the SOD1 electrostatic channel loop, but lacks many of the residues important for catalysis. Like SOD1 and yCCS, hCCS forms a dimer using a highly conserved interface. In contrast to SOD1, however, the hCCS structure does not contain a copper ion bound in the catalytic site. Notably, the structure reveals a single loop proximal to the dimer interface which is unique to the CCS chaperones.     

Lipid‐associated aggregate formation of superoxide dismutase‐1 is initiated by membrane‐targeting loops

Copper‐Zinc superoxide dismutase 1 (SOD1) is a homodimeric enzyme that protects cells from oxidative damage. Hereditary and sporadic amyotrophic lateral sclerosis may be linked to SOD1 when the enzyme is destabilized through mutation or environmental stress. The cytotoxicity of demetallated or apo‐SOD1 aggregates may be due to their ability to cause defects within cell membranes by co‐aggregating with phospholipids. SOD1 monomers may associate with the inner cell membrane to receive copper ions from membrane‐bound copper chaperones. But how apo‐SOD1 interacts with lipids is unclear. We have used atomistic molecular dynamics simulations to reveal that flexible electrostatic and zinc‐binding loops in apo‐SOD1 dimers play a critical role in the binding of 1‐octanol clusters and phospholipid bilayer, without any significant unfolding of the protein. The apo‐SOD1 monomer also associates with phospholipid bilayer via its zinc‐binding loop rather than its exposed hydrophobic dimerization interface. Our observed orientation of the monomer on the bilayer would facilitate its association with a membrane‐bound copper chaperone. The orientation also suggests how membrane‐bound monomers could act as seeds for membrane‐associated SOD1 aggregation. Proteins 2014; 82:3194–3209. © 2014 Wiley Periodicals, Inc.     

Unfolding and folding kinetics of amyotrophic lateral sclerosis-associated mutant Cu,Zn superoxide dismutases

More than 110 mutations in dimeric, Cu,Zn superoxide dismutase (SOD) have been linked to the fatal neurodegenerative disease, amyotrophic lateral sclerosis (ALS). In both human patients and mouse model studies, protein misfolding has been implicated in disease pathogenesis. A central step in understanding the misfolding/aggregation mechanism of this protein is the elucidation of the folding pathway of SOD. Here we report a systematic analyses of unfolding and folding kinetics using single- and double-jump experiments as well as measurements as a function of guanidium chloride, protein, and metal concentration for fully metallated (holo) pseudo wild-type and ALS-associated mutant (E100G, G93R, G93A, and metal binding mutants G85R and H46R) SODs. The kinetic mechanism for holo SODs involves native dimer, monomer intermediate, and unfolded monomer, with variable metal dissociation from the monomeric states depending on solution conditions. The effects of the ALS mutations on the kinetics of the holoproteins in guanidium chloride are markedly different from those observed previously for acid-induced unfolding and for the unmetallated (apo) forms of the proteins. The mutations decrease the stability of holo SOD mainly by increasing unfolding rates, which is particularly pronounced for the metal-binding mutants, and have relatively smaller effects on the observed folding kinetics. Mutations also seem to favour increased formation of a Zn-free monomer intermediate, which has been implicated in the formation of toxic aggregates. The results reveal the kinetic basis for the extremely high stability of wild-type holo SOD and the possible consequences of kinetic changes for disease.     

Structural characterization of zinc-deficient human superoxide dismutase and implications for ALS

Over 130 mutations to copper, zinc superoxide dismutase (SOD) are implicated in the selective death of motor neurons found in 25% of patients with familial amyotrophic lateral sclerosis (ALS). Despite their widespread distribution, ALS mutations appear positioned to cause structural and misfolding defects. Such defects decrease SOD's affinity for zinc, and loss of zinc from SOD is sufficient to induce apoptosis in motor neurons in vitro. To examine the importance of the zinc site in the structure and pathogenesis of human SOD, we determined the 2.0-A-resolution crystal structure of a designed zinc-deficient human SOD, in which two zinc-binding ligands have been mutated to hydrogen-bonding serine residues. This structure revealed a 9 degrees twist of the subunits, which opens the SOD dimer interface and represents the largest intersubunit rotational shift observed for a human SOD variant. Furthermore, the electrostatic loop and zinc-binding subloop were partly disordered, the catalytically important Arg143 was rotated away from the active site, and the normally rigid intramolecular Cys57-Cys146 disulfide bridge assumed two conformations. Together, these changes allow small molecules greater access to the catalytic copper, consistent with the observed increased redox activity of zinc-deficient SOD. Moreover, the dimer interface is weakened and the Cys57-Cys146 disulfide is more labile, as demonstrated by the increased aggregation of zinc-deficient SOD in the presence of a thiol reductant. However, equimolar Cu,Zn SOD rapidly forms heterodimers with zinc-deficient SOD (t1/2 approximately 15 min) and prevents aggregation. The stabilization of zinc-deficient SOD as a heterodimer with Cu,Zn SOD may contribute to the dominant inheritance of ALS mutations. These results have general implications for the importance of framework stability on normal metalloenzyme function and specific implications for the role of zinc ion in the fatal neuropathology associated with SOD mutations.     

Dysregulation of intracellular copper trafficking pathway in a mouse model of mutant copper/zinc superoxide dismutase-linked familial amyotrophic lateral sclerosis

Mutations in copper/zinc superoxide dismutase (SOD1) are responsible for 20% of familial amyotrophic lateral sclerosis through a gain-of-toxic function. We have recently shown that ammonium tetrathiomolybdate, an intracellular copper-chelating reagent, has an excellent therapeutic benefit in a mouse model for amyotrophic lateral sclerosis. This finding suggests that mutant SOD1 might disrupt intracellular copper homeostasis. In this study, we investigated the effects of mutant SOD1 on the components of the copper trafficking pathway, which regulate intracellular copper homeostasis. We found that mutant, but not wild-type, SOD1 shifts intracellular copper homeostasis toward copper accumulation in the spinal cord during disease progression: copper influx increases, copper chaperones are up-regulated, and copper efflux decreases. This dysregulation was observed within spinal motor neurons and was proportionally associated with an age-dependent increase in spinal copper ion levels. We also found that a subset of the copper trafficking pathway constituents co-aggregated with mutant SOD1. These results indicate that the nature of mutant SOD1 toxicity might involve the dysregulation of the copper trafficking pathway, resulting in the disruption of intracellular copper homeostasis.     

Dissociation and unfolding of cold-active alkaline phosphatase from atlantic cod in the presence of guanidinium chloride.

Cold-adaptation of enzymes involves improvements in catalytic efficiency. This paper describes studies on the conformational stability of a cold-active alkaline phosphatase (AP) from Atlantic cod, with the aim of understanding more clearly its structural stability in terms of subunit dissociation and unfolding of monomers. AP is a homodimeric enzyme that is only active in the dimeric state. Tryptophan fluorescence, size-exclusion chromatography and enzyme activity were used to monitor alterations in conformational state induced by guanidinium chloride or urea. In cod AP, a clear distinction could be made between dissociation of dimers into monomers and subsequent unfolding of monomers (fits a three-state model). In contrast, dimer dissociation of calf AP coincided with the monophasic unfolding curve observed by tryptophan fluorescence (fits a two-state model). The DeltaG for dimer dissociation of cod AP was 8.3 kcal.mol-1, and the monomer stabilization free energy was 2.2 kcal.mol-1, giving a total of 12.7 kcal.mol-1, whereas the total free energy of calf intestinal AP was 17.3 kcal.mol-1. Thus, dimer formation provided a major contribution to the overall stability of the cod enzyme. Phosphate, the reaction product, had the effect of promoting dimer dissociation and stabilizing the monomers. Cod AP has reduced affinity for inorganic phosphate, the release of which is the rate-limiting step of the reaction mechanism. More flexible links at the interface between the dimer subunits may ease structural rearrangements that facilitate more rapid release of phosphate, and thus catalytic turnover.     

Copper and zinc metallation status of copper-zinc superoxide dismutase from amyotrophic lateral sclerosis transgenic mice

Mutations in the metalloenzyme copper-zinc superoxide dismutase (SOD1) cause one form of familial amyotrophic lateral sclerosis (ALS), and metals are suspected to play a pivotal role in ALS pathology. To learn more about metals in ALS, we determined the metallation states of human wild-type or mutant (G37R, G93A, and H46R/H48Q) SOD1 proteins from SOD1-ALS transgenic mice spinal cords. SOD1 was gently extracted from spinal cord and separated into insoluble (aggregated) and soluble (supernatant) fractions, and then metallation states were determined by HPLC inductively coupled plasma MS. Insoluble SOD1-rich fractions were not enriched in copper and zinc. However, the soluble mutant and WT SOD1s were highly metallated except for the metal-binding-region mutant H46R/H48Q, which did not bind any copper. Due to the stability conferred by high metallation of G37R and G93A, it is unlikely that these soluble SOD1s are prone to aggregation in vivo, supporting the hypothesis that immature nascent SOD1 is the substrate for aggregation. We also investigated the effect of SOD1 overexpression and disease on metal homeostasis in spinal cord cross-sections of SOD1-ALS mice using synchrotron-based x-ray fluorescence microscopy. In each mouse genotype, except for the H46R/H48Q mouse, we found a redistribution of copper between gray and white matters correlated to areas of high SOD1. Interestingly, a disease-specific increase of zinc was observed in the white matter for all mutant SOD1 mice. Together these data provide a picture of copper and zinc in the cell as well as highlight the importance of these metals in understanding SOD1-ALS pathology.     

Equilibrium thermodynamic analysis of amyotrophic lateral sclerosis-associated mutant apo Cu,Zn superoxide dismutases

The folding and thermodynamic properties of metal free (apo) superoxide dismutases (SODs) are systematically analyzed using equilibrium guanidinium chloride (GdmCl) curves and differential scanning calorimetry (DSC). Chemically and structurally diverse amyotrophic lateral sclerosis (ALS)-associated mutations (G85R, G93R, E100G, I113T) are introduced into a pseudo-wild-type background that has no free cysteines, resulting in highly reversible unfolding. Analysis of the protein concentration dependence of GdmCl curves reveals formation of a monomer intermediate in equilibrium with native dimer and unfolded monomer. Global fitting of the data enables quantitative measurement of free energy changes for both dimer dissociation and monomer intermediate stability. All the mutations decrease protein stability, mainly by destabilizing the monomer intermediate, but also by tending to weaken dimerization, even for mutations far from the dimer interface. Thus, the effects of mutations seem to propagate through the apo protein, and result in increased population of both intermediate and unfolded monomers. This may underlie increased formation of toxic aggregates by mutants in ALS. Analysis of DSC data for apo SODs is consistent with stability measurements from GdmCl curves and provides further evidence for increased aggregation by mutant proteins through increased ratios of van't Hoff to calorimetric enthalpies of unfolding.     

The coupling between disulphide status, metallation and dimer interface strength in Cu/Zn superoxide dismutase

The gain of neurotoxic function in amyotrophic lateral sclerosis (ALS) has been linked to misfolding of the homodimeric enzyme Cu/Zn superoxide dismutase (SOD). Here, we present the crystal structure of fully cysteine-depleted human SOD (SOD(CallA)), representing a reduced, marginally stable intermediate on the folding pathway in vivo that has also been implicated as neurotoxic precursor state. A hallmark of this species is that it fails to dimerize and becomes trapped as a monomer in the absence of the active-site metals. The crystallographic data show that removal of the C57-C146 disulphide bond sets free the interface loop IV in the apo protein, whereas the same loop remains unaffected in the holo protein. Thus, the low dimerisation propensity of disulphide-reduced apoSOD seems to be of entropic origin due to increased loop flexibility in the monomeric state: in the disulphide-reduced holo protein this gain in configurational entropy upon splitting of the dimer interface is reduced by the metal coordination.     

An intersubunit disulfide bond prevents in vitro aggregation of a superoxide dismutase-1 mutant linked to familial amytrophic lateral sclerosis

Familial amyotrophic lateral sclerosis (FALS) is linked to over 90 point mutations in superoxide dismutase-1 (SOD1), a dimeric metalloenzyme. The postmortem FALS brain is characterized by SOD1 inclusions in the motor neurons of regions in which neuronal loss is most significant. These findings, together with animal modeling studies, suggest that aggregation of mutant SOD1 produces a pathogenic species. We demonstrate here that a mutant form of SOD1 (A4V) that is linked to a particularly aggressive form of FALS aggregates in vitro, while wild-type SOD1 (WT) is stable. Some A4V aggregates resemble amyloid pores formed by other disease-associated proteins. The WT dimer is significantly more stable than the A4V dimer, suggesting that dimer dissociation may be the required first step of aggregation. To test this hypothesis, an intersubunit disulfide bond between symmetry-related residues at the A4V dimer interface was introduced. The resultant disulfide bond (V148C-V148C') eliminated the concentration-dependent loss of enzymatic activity of A4V, stabilized the A4V dimer, and completely abolished aggregation. A drug-like molecule that could stabilize the A4V dimer could slow the onset and progression of FALS.     

Capillary electrophoresis study on the dimeric SOD enzyme in the presence of ascorbic acid

A Notable decrease of the peak intensity of the capillary electrophoregram due to the dimeric SOD molecule was observed when a solution containing copper(II) chloride and ascorbic acid was added to the SOD solution, indicating that the capillary electrophoresis method is useful to detect the dissociation of the dimeric SOD molecule in solution, and that dissociation of the dimeric SOD molecule is induced by the presence of hydrogen peroxide. The present results may give reasonable countermeasures towards the sporadic amyotrophic lateral sclerosis in future.     

Misfolded superoxide dismutase-1 in CSF from amyotrophic lateral sclerosis patients

Several of the superoxide dismutase-1 (SOD1) mutations linked to amyotrophic lateral sclerosis (ALS) lead to synthesis of structurally defective molecules, suggesting that any cytotoxic conformational species common for all mutations should be misfolded. SOD1 can be secreted and evidence from ALS model systems suggests that extracellular SOD1 may be involved in cytotoxicity. Three ELISAs specifically reacting with different sequence segments in misfolded SOD1 species were used for analysis of CSF from 38 neurological controls and from 96 ALS patients, 57 of whom were sporadic cases and 39 familial, including 22 patients carrying SOD1 mutations. Misfolded SOD1 was found in all samples. There were, however, no significant differences between patients with and without mutations, and between all the ALS patients and the controls. The estimated concentration of misfolded SOD1 in the interstitium of the CNS is a 1000 times lower than that required for appreciable cytotoxicity in model systems. The results argue against a direct cytotoxic role of extracellular misfolded SOD1 in ALS. Misfolded SOD1 in CSF cannot be used as a biomarker of ALS in patients with and without mutations in the enzyme.     

Different immunoreactivity against monoclonal antibodies between wild-type and mutant copper/zinc superoxide dismutase linked to amyotrophic lateral sclerosis

Although more than 100 mutations have been identified in the copper/zinc superoxide dismutase (Cu/Zn-SOD) in familial amyotrophic lateral sclerosis (FALS), the mechanism responsible for FALS remains unclear. The finding of the present study shows that FALS-causing mutant Cu/Zn-SOD proteins (FALS mutant SODs), but not wild-type SOD, are barely detected by three monoclonal antibodies (mAbs) in Western blot analyses. The enzyme-linked immunosorbent assay for denatured FALS mutant SODs by dithiothreitol, SDS, or heat treatment also showed a lowered immunoreactivity against the mAbs compared with wild-type SOD. Because all the epitopes of these mAbs are mapped within the Greek key loop (residues 102-115 in human Cu/Zn-SOD), these data suggest that different conformational changes occur in the loop between wild-type and FALS mutant SODs during the unfolding process. Circular dichroism measurements revealed that the FALS mutant SODs are sensitive to denaturation by dithiothreitol, SDS, or heat treatment, but these results do not completely explain the different recognition by the mAbs between wild-type and FALS mutant SODs under the denatured conditions. The study on the conformational changes in local areas monitoring with mAbs may provide a new insight into the etiology of FALS.