Abundant fish protein inhibits α-synuclein amyloid formation

Amyloids of α-Synuclein Promote Chemical Transformations of Neuronal Cell Metabolites

The assembly of α-synuclein into cross-β structured amyloid fibers results in Lewy body deposits and neuronal degeneration in Parkinson's disease patients. As the cell environment is highly crowded, interactions between the formed amyloid fibers and a range of biomolecules can occur in cells. Although amyloid fibers are considered chemically inert species, recent in vitro work using model substrates has shown α-synuclein amyloids, but not monomers, to catalyze the hydrolysis of ester and phosphoester bonds. To search for putative catalytic activity of α-synuclein amyloids on biologically relevant metabolites, we here incubated α-synuclein amyloids with neuronal SH-SY5Y cell lysates devoid of proteins. LC-MS-based metabolomic (principal component and univariate) analysis unraveled distinct changes in several metabolite levels upon amyloid (but not monomer) incubation. Of 63 metabolites identified, the amounts of four increased (3-hydroxycapric acid, 2-pyrocatechuic acid, adenosine, and NAD), and the amounts of seventeen decreased (including aromatic and apolar amino acids, metabolites in the TCA cycle, keto acids) in the presence of α-synuclein amyloids. Many of these metabolite changes match what has been reported previously in Parkinson's disease patients and animal-model metabolomics studies. Chemical reactivity of α-synuclein amyloids may be a new gain-of-function that alters the metabolite composition in cells and, thereby, modulates disease progression.

Could the Urease of the Gut Bacterium Proteus mirabilis Play a Role in the Altered Gut-Brain Talk Associated with Parkinson's Disease?

Intestinal dysbiosis seems to play a role in neurodegenerative pathologies. Parkinson's disease (PD) patients have an altered gut microbiota. Moreover, mice treated orally with the gut microbe Proteus mirabilis developed Parkinson's-like symptoms. Here, the possible involvement of P. mirabilis urease (PMU) and its B subunit (PmUreβ) in the pathogenesis of PD was assessed. Purified proteins were given to mice intraperitoneally (20 μg/animal/day) for one week. Behavioral tests were conducted, and brain homogenates of the treated animals were subjected to immunoassays. After treatment with PMU, the levels of TNF-α and IL-1β were measured in Caco2 cells and cellular permeability was assayed in Hek 293. The proteins were incubated in vitro with α-synuclein and examined via transmission electron microscopy. Our results showed that PMU treatment induced depressive-like behavior in mice. No motor deficits were observed. The brain homogenates had an increased content of caspase-9, while the levels of α-synuclein and tyrosine hydroxylase decreased. PMU increased the pro-inflammatory cytokines and altered the cellular permeability in cultured cells. The urease, but not the PmUreβ, altered the morphology of α-synuclein aggregates in vitro, forming fragmented aggregates. We concluded that PMU promotes pro-inflammatory effects in cultured cells. In vivo, PMU induces neuroinflammation and a depressive-like phenotype compatible with the first stages of PD development.

Distinct growth regimes of α-synuclein amyloid elongation

Addition of amyloid seeds to aggregation-prone monomers allows for amyloid fiber growth (elongation) omitting slow nucleation. We here combine Thioflavin T fluorescence (probing formation of amyloids) and solution-state NMR spectroscopy (probing disappearance of monomers) to assess elongation kinetics of the amyloidogenic protein, α-synuclein, for which aggregation is linked to Parkinson's disease. We found that both spectroscopic detection methods give similar kinetic results, which can be fitted by applying double exponential decay functions. When the origin of the two-phase behavior was analyzed by mathematical modeling, parallel paths as well as stop-and-go behavior were excluded as possible explanations. Instead, supported by previous theory, the experimental elongation data reveal distinct kinetic regimes that depend on instantaneous monomer concentration. At low monomer concentrations (toward end of experiments), amyloid growth is limited by conformational changes resulting in β-strand alignments. At the higher monomer concentrations (initial time points of experiments), growth occurs rapidly by incorporating monomers that have not successfully completed the conformational search. The presence of a fast disordered elongation regime at high monomer concentrations agrees with coarse-grained simulations and theory but has not been detected experimentally before. Our results may be related to the wide range of amyloid folds observed.

Structural Specificity of Polymorphic Forms of α-Synuclein Amyloid

The structural transformation producing amyloids is a phenomenon that sheds new light on the protein folding problem. The analysis of the polymorphic structures of the α-synuclein amyloid available in the PDB database allows analysis of the amyloid-oriented structural transformation itself, but also the protein folding process as such. The polymorphic amyloid structures of α-synuclein analyzed employing the hydrophobicity distribution (fuzzy oil drop model) reveal a differentiation with a dominant distribution consistent with the micelle-like system (hydrophobic core with polar shell). This type of ordering of the hydrophobicity distribution covers the entire spectrum from the example with all three structural units (single chain, proto-fibril, super-fibril) exhibiting micelle-like form, through gradually emerging examples of local disorder, to structures with an extremely different structuring pattern. The water environment directing protein structures towards the generation of ribbon micelle-like structures (concentration of hydrophobic residues in the center of the molecule forming a hydrophobic core with the exposure of polar residues on the surface) also plays a role in the amyloid forms of α-synuclein. The polymorphic forms of α-synuclein reveal local structural differentiation with a common tendency to accept the micelle-like structuralization in certain common fragments of the polypeptide chain of this protein.

Amyloid Fibers of α-Synuclein Catalyze Chemical Reactions

Amyloid fibers of the protein α-synuclein, found in Lewy body deposits, are hallmarks of Parkinson's disease. We here show that α-synuclein amyloids catalyze biologically relevant chemical reactions in vitro. Amyloid fibers, but not monomers, of α-synuclein catalyzed hydrolysis of the model ester para-nitrophenyl acetate and dephosphorylation of the model phosphoester para-nitrophenyl-orthophosphate. When His50 was replaced with Ala in α-synuclein, dephosphorylation but not esterase activity of amyloids was diminished. Truncation of the protein's C-terminus had no effect on fiber catalytic efficiency. Catalytic activity of α-synuclein fibers may be a new gain-of-function that plays a role in Parkinson's disease.

Food protein-derived amyloids do not accelerate amyloid β aggregation

The deposition of proteins in the form of amyloid fibrils is closely associated with several serious diseases. The events that trigger the conversion from soluble functional proteins into insoluble amyloid are not fully understood. Many proteins that are not associated with disease can form amyloid with similar structural characteristics as the disease-associated fibrils, which highlights the potential risk of cross-seeding of disease amyloid by amyloid-like structures encountered in our surrounding. Of particular interest are common food proteins that can be transformed into amyloid under conditions similar to cooking. We here investigate cross-seeding of amyloid-β (Aβ), a peptide known to form amyloid during the development of Alzheimer's disease, by 16 types of amyloid fibrils derived from food proteins or peptides. Kinetic studies using thioflavin T fluorescence as output show that none of the investigated protein fibrils accelerates the aggregation of Aβ. In at least two cases (hen egg lysozyme and oat protein isolate) we observe retardation of the aggregation, which appears to originate from interactions between the food protein seeds and Aβ in aggregated form. The results support the view that food-derived amyloid is not a risk factor for development of Aβ pathology and Alzheimer's disease.

Protective Effects of Fish (Alaska Pollock) Protein Intake against Short-Term Memory Decline in Senescence-Accelerated Mice

Dietary fish intake has proven to have health benefits in humans. n-3 polyunsaturated fatty acids (PUFAs) in fish oil (FO), especially, may provide protection against age-related cognitive disorders. Owing to the unique benefits of n-3 PUFAs, other nutrients, such as fish protein (FP), have not been well studied. To clarify the effects of FO and FP on brain function, we investigated whether FO or FP feeding can prevent age-related cognitive dysfunction in senescence-accelerated mouse-prone 10 (SAMP10) mice. The FP group maintained a better working memory compared to the control and FO groups in the Y-maze test, but not episodic memory in the novel object recognition test. To evaluate demyelination levels, we measured neurofilament H (NfH) and myelin basic protein (MBP) immunoreactivity in the hippocampus (Hipp). Axon morphology was maintained in the FP group, but not in the control and FO groups. Additionally, the percentage of positive area for double-staining with NfH/MPB was significantly higher in the Hipp of FP-fed mice than in the control (p < 0.05). These results suggest that FP intake prevents age-related cognitive dysfunction by maintaining axonal morphology in the Hipp of SAMP10 mice.

Microbiome Impact on Amyloidogenesis

Our life is closely linked to microorganisms, either through a parasitic or symbiotic relationship. The microbiome contains more than 1,000 different bacterial species and outnumbers human genes by 150 times. Worryingly, during the last 10 years, it has been observed a relationship between alterations in microbiota and neurodegeneration. Several publications support the hypothesis that amyloid structures formed by microorganisms may trigger host proteins aggregation. In this review, we collect pieces of evidence supporting that the crosstalk between human and microbiota amyloid proteins could be feasible and, probably, a more common event than expected before. The combination of their outnumbers, the long periods of time that stay in our bodies, and the widespread presence of amyloid proteins in the bacteria Domain outline a worrying scenario. However, the identification of the exact microorganisms and the mechanisms through with they can influence human disease also opens the door to developing a new and diverse set of therapeutic strategies.

Impact of air pollution exposure on the risk of Alzheimer's disease in China: A community-based cohort study

Alzheimer's disease (AD) is the most common type of dementia. Impact of air pollution (AP) on the risk of AD is unclear. It is unknown which air pollutants are independently associated with AD and whether fish consumption mitigated the association. We carried out a community-based cohort of 6115 participants aged ≥60 years in China to examine the association of PM_2.5, PM₁₀, CO, NO₂, SO₂ and O₃ exposure with AD, and differences in the association between people with low and high consumption of fish. The participants were randomly recruited from six counties in Zhejiang province for health survey to document socio-demographic and disease risk factors in 2014, and were followed up to diagnose AD in 2019. A total of 986 cohort members were diagnosed with AD. Based on the daily mean air pollutants monitored in 2013-2015 in the counties, participants were divided into low, middle and high AP exposure groups for subsequent analysis. The multiple adjusted odds ratio (OR) of AD in participants living with the middle and high levels of PM_2.5 exposure versus the low exposure were 1.50 (95% CI 0.90-2.50) and 3.92 (2.09-7.37). The increased ORs were also with PM₁₀ (1.74, 0.65-4.64; 3.00, 1.22-7.41) and CO (2.86, 1.32-6.20; 1.19, 0.45-3.18), but not with NO₂ (0.63, 0.17-2.27; 0.95, 0.28-3.19), SO₂ (0.44, 0.19-1.001; 1.21, 0.56-2.62), and O₃ (0.38, 0.20-0.74; 0.50, 0.21-1.21). There were no significant interaction effects of AP with fish consumption on AD. However, participants with low consumption of fish appeared to have higher ORs in PM_2.5 exposure (1.80, 1.39-2.33; 5.18, 3.93-6.82) than those high consumption (1.38, 0.78-2.47; 2.89, 1.50-5.59). Our findings of PM_2.5, PM₁₀ and CO exposure significantly increased the risk of AD and the potential mitigating effect of fish consumption on the association provide evidence for developing effective strategies for AD reduction and air pollution control.

The copper chaperone CCS facilitates copper binding to MEK1/2 to promote kinase activation

Normal physiology relies on the precise coordination of intracellular signal transduction pathways that respond to nutrient availability to balance cell growth and cell death. The canonical MAPK pathway consists of the RAF-MEK-ERK signaling cascade and represents one of the most well-defined axes within eukaryotic cells to promote cell proliferation, which underscores its frequent mutational activation in the majority of human cancers. Our recent studies illuminated a function for the redox-active micronutrient copper (Cu) as an intracellular mediator of signaling by connecting Cu to the amplitude of MAPK signaling via a direct interaction between Cu and the kinases MEK1 and MEK2. Given the large quantities of molecules like glutathione and metallothionein that limit cellular toxicity from free Cu ions, evolutionarily conserved Cu chaperones facilitate the efficient delivery of Cu to cuproenzymes. Thus, a dedicated cellular delivery mechanism of Cu to MEK1/2 is likely to exist. Using surface plasmon resonance and proximity-dependent biotin ligase studies, we report here that the Cu chaperone CCS selectively bound to and facilitated Cu transfer to MEK1. Mutations in CCS that disrupt Cu(I) acquisition and exchange or a CCS small molecule inhibitor were employed and resulted in reduced Cu-stimulated MEK1 kinase activity. Our findings indicate that the Cu chaperone CCS provides fidelity within a complex biological system to achieve appropriate installation of Cu within the MEK1 kinase active site that in turn modulates kinase activity and support the development of novel MEK1/2 inhibitors that target the Cu structural interface or blunt dedicated Cu delivery mechanisms via CCS.

Gut power: Modulation of human amyloid formation by amyloidogenic proteins in the gastrointestinal tract

Protein assembly into amyloid fibers underlies many neurodegenerative disorders. In Parkinson's disease, amyloid formation of α-synuclein is linked to brain cell death. The gut-brain axis plays a key role in Parkinson's disease, and initial α-synuclein amyloid formation may occur distant from the brain. Because different amyloidogenic proteins can cross-seed, and α-synuclein is expressed outside the brain, amyloids present in the gut (from food products and secreted by microbiota) may modulate α-synuclein amyloid formation via direct interactions. I here describe existing such data that only began to appear in the literature in the last few years. The striking, but limited, data set-spanning from acceleration to inhibition-calls for additional investigations that may unravel disease mechanisms as well as new treatments.

Macromolecular crowding modulates α-synuclein amyloid fiber growth

The crowdedness of living cells, hundreds of milligrams per milliliter of macromolecules, may affect protein folding, function, and misfolding. Still, such processes are most often studied in dilute solutions in vitro. To assess consequences of the in vivo milieu, we here investigated the effects of macromolecular crowding on the amyloid fiber formation reaction of α-synuclein, the amyloidogenic protein in Parkinson's disease. For this, we performed spectroscopic experiments probing individual steps of the reaction as a function of the macromolecular crowding agent Ficoll70, which is an inert sucrose-based polymer that provides excluded-volume effects. The experiments were performed at neutral pH at quiescent conditions to avoid artifacts due to shaking and glass beads (typical conditions for α-synuclein), using amyloid fiber seeds to initiate reactions. We find that both primary nucleation and fiber elongation steps during α-synuclein amyloid formation are accelerated by the presence of 140 and 280 mg/mL Ficoll70. Moreover, in the presence of Ficoll70 at neutral pH, secondary nucleation appears favored, resulting in faster overall α-synuclein amyloid formation. In contrast, sucrose, a small-molecule osmolyte and building block of Ficoll70, slowed down α-synuclein amyloid formation. The ability of cell environments to modulate reaction kinetics to a large extent, such as severalfold faster individual steps in α-synuclein amyloid formation, is an important consideration for biochemical reactions in living systems.

The intestinal luminal sources of α-synuclein: a gastroenterologist perspective

Parkinson's disease is characterized by nonmotor/motor dysfunction, midbrain dopaminergic neuronal death, and α-synuclein (aSN) deposits. The current hypothesis is that aSN accumulates in the enteric nervous system to reach the brain. However, invertebrate, vertebrate, and nutritional sources of aSN reach the luminal compartment. Submitted to local amyloidogenic forces, the oligomerized proteins' cargo can be sensed and sampled by a specialized mucosal cell to be transmitted to the adjacent enteric nervous system, starting their upward journey to the brain. The present narrative review extends the current mucosal origin of Parkinson's disease, presenting the possibility that the disease starts in the intestinal lumen. If substantiated, eliminating the nutritional sources of aSN (eg, applying a vegetarian diet) might revolutionize the currently used dopaminergic pharmacologic therapy.

Response to crowded conditions reveals compact nucleus for amyloid formation of folded protein

Although the consequences of the crowded cell environments may affect protein folding, function and misfolding reactions, these processes are often studied in dilute solutions in vitro. We here used biophysical experiments to investigate the amyloid fibril formation process of the fish protein apo-β-parvalbumin in solvent conditions that mimic steric and solvation aspects of the in vivo milieu. Apo-β-parvalbumin is a folded protein that readily adopts an amyloid state via a nucleation–elongation mechanism. Aggregation experiments in the presence of macromolecular crowding agents (probing excluded volume, entropic effects) as well as small molecule osmolytes (probing solvation, enthalpic effects) revealed that both types of agents accelerate overall amyloid formation, but the elongation step was faster with macromolecular crowding agents but slower in the presence of osmolytes. The observations can be explained by the steric effects of excluded volume favoring assembled states and that amyloid nucleation does not involve monomer unfolding. In contrast, the solvation effects due to osmolyte presence promote nucleation but not elongation. Therefore, the amyloid-competent nuclei must be compact with less osmolytes excluded from the surface than either the folded monomers or amyloid fibers. We conclude that, in contrast to other amyloidogenic folded proteins, amyloid formation of apo-β-parvalbumin is accelerated by crowded cell-like conditions due to a nucleation process that does not involve large-scale protein unfolding.

Amyloid formation of fish β-parvalbumin involves primary nucleation triggered by disulfide-bridged protein dimers

Amyloid fibrils are generally related to neurodegenerative diseases, but they can also be part of normal protein function. Amyloid formation involves numerous steps and intermediate species. In this study, we investigated a fish protein, beta-parvalbumin, which readily forms amyloid on ligand removal. Using biophysical experiments, we provide evidence that the underlying mechanism of amyloid formation includes primary nucleation and elongation processes; we also reveal a key role for a disulfide-bridged dimer in the nucleation step. Little is known about intermolecular disulfides in amyloid formation, but covalent dimers and dimer-induced aggregation may be of clinical relevance, because oxidative stress, which can trigger covalent bond formation, is often a hallmark of human neurodegenerative diseases.

Amyloid formation involves the conversion of soluble protein species to an aggregated state. Amyloid fibrils of β-parvalbumin, a protein abundant in fish, act as an allergen but also inhibit the in vitro assembly of the Parkinson protein α-synuclein. However, the intrinsic aggregation mechanism of β-parvalbumin has not yet been elucidated. We performed biophysical experiments in combination with mathematical modeling of aggregation kinetics and discovered that the aggregation of β-parvalbumin is initiated by the formation of dimers stabilized by disulfide bonds and then proceeds via primary nucleation and fibril elongation processes. Dimer formation is accelerated by H₂O₂ and hindered by reducing agents, resulting in faster and slower aggregation rates, respectively. Purified β-parvalbumin dimers readily assemble into amyloid fibrils with similar morphology as those formed when starting from monomer solutions. Furthermore, addition of preformed dimers accelerates the aggregation reaction of monomers. Aggregation of purified β-parvalbumin dimers follows the same kinetic mechanism as that of monomers, implying that the rate-limiting primary nucleus is larger than a dimer and/or involves structural conversion. Our findings demonstrate a folded protein system in which spontaneously formed intermolecular disulfide bonds initiate amyloid fibril formation by recruitment of monomers. This dimer-induced aggregation mechanism may be of relevance for human amyloid diseases in which oxidative stress is often an associated hallmark.

Graphene oxide sheets and quantum dots inhibit α-synuclein amyloid formation by different mechanisms

Aggregation and amyloid formation of the 140-residue presynaptic and intrinsically disordered protein α-synuclein (α-syn) is a pathological hallmark of Parkinson's disease (PD). Understanding how α-syn forms amyloid fibrils, and investigations of agents that can prevent their formation is therefore important. We demonstrate herein that two types of graphene oxide nanoparticles (sheets and quantum dots) inhibit α-syn amyloid formation by different mechanisms mediated via differential interactions with both monomers and fibrils. We have used thioflavin-T fluorescence assays and kinetic analysis, circular dichroism, dynamic light scattering, fluorescence spectroscopy and atomic force microscopy to asses the kinetic nature and efficiency of this inhibitory effect. We show that the two types of graphene oxide nanoparticles alter the morphology of α-syn fibrils, disrupting their interfilament assembly and the resulting aggregates therefore consist of single protofilaments. Our results further show that graphene oxide sheets reduce the aggregation rate of α-syn primarily by sequestering of monomers, thereby preventing primary nucleation and elongation. Graphene quantum dots, on the other hand, interact less avidly with both monomers and fibrils. Their aggregation inhibitory effect is primarily related to adsorption of aggregated species and reduction of secondary processes, and they can thus not fully prevent aggregation. This fine-tuned and differential effect of graphene nanoparticles on amyloid formation shows that rational design of these nanomaterials has great potential in engineering materials that interact with specific molecular events in the amyloid fibril formation process. The findings also provide new insight into the molecular interplay between amyloidogenic proteins and graphene-based nanomaterials in general, and opens up their potential use as agents to manipulate fibril formation.

Brain foods - the role of diet in brain performance and health

The performance of the human brain is based on an interplay between the inherited genotype and external environmental factors, including diet. Food and nutrition, essential in maintenance of brain performance, also aid in prevention and treatment of mental disorders. Both the overall composition of the human diet and specific dietary components have been shown to have an impact on brain function in various experimental models and epidemiological studies. This narrative review provides an overview of the role of diet in 5 key areas of brain function related to mental health and performance, including: (1) brain development, (2) signaling networks and neurotransmitters in the brain, (3) cognition and memory, (4) the balance between protein formation and degradation, and (5) deteriorative effects due to chronic inflammatory processes. Finally, the role of diet in epigenetic regulation of brain physiology is discussed.

Differential effects of Cu2+ and Fe3+ ions on in vitro amyloid formation of biologically-relevant α-synuclein variants

Alterations in metal ion homeostasis appear coupled to neurodegenerative disorders but mechanisms are unknown. Amyloid formation of the protein α-synuclein in brain cells is a hallmark of Parkinson's disease. α-Synuclein can bind several metal ions in vitro and such interactions may affect the assembly process. Here we used biophysical methods to study the effects of micromolar concentrations of Cu²⁺ and Fe³⁺ ions on amyloid formation of selected α-synuclein variants (wild-type and A53T α-synuclein, in normal and N-terminally acetylated forms). As shown previously, Cu²⁺ speeds up aggregation of normal wild-type α-synuclein, but not the acetylated form. However, Cu²⁺ has a minimal effect on (the faster) aggregation of normal A53T α-synuclein, despite that Cu²⁺ binds to this variant. Like Cu²⁺, Fe³⁺ speeds up aggregation of non-acetylated wild-type α-synuclein, but with acetylation, Fe³⁺ instead slows down aggregation. In contrast, for A53T α-synuclein, regardless of acetylation, Fe³⁺ slows down aggregation with the effect being most dramatic for acetylated A53T α-synuclein. The results presented here suggest a correlation between metal-ion modulation effect and intrinsic aggregation speed of the various α-synuclein variants.

Correlation between Cellular Uptake and Cytotoxicity of Fragmented α-Synuclein Amyloid Fibrils Suggests Intracellular Basis for Toxicity

Aggregation and intracellular deposition of the protein α-synuclein is an underlying characteristic of Parkinson's disease. α-Synuclein assemblies also undergo cell-cell spreading, facilitating propagation of their cellular pathology. Understanding how cellular interactions and uptake of extracellular α-synuclein assemblies depend on their physical attributes is therefore important. We prepared fragmented fluorescently labeled α-synuclein amyloid fibrils of different average lengths (∼80 nm to >1 μm) and compared their interactions with SH-SY5Y cells. We report that fibrils of all lengths, but not monomers, bind avidly to the cell surface. Their uptake is inversely dependent on their average size, occurs via a heparan sulfate dependent endocytic route, and appears to have a size cutoff of ∼400 nm. The uptake of α-synuclein fibrils, but not monomers, correlates with their cytotoxicity as measured by reduction in metabolic activity, strongly suggesting an intracellular basis for α-synuclein fibril toxicity, likely involving endolysosomes.

Crosstalk Between Alpha-Synuclein and Other Human and Non-Human Amyloidogenic Proteins: Consequences for Amyloid Formation in Parkinson's Disease

It was recently shown (Sampson et al., Elife9, 2020) that an amyloidogenic protein, CsgA, present in E. coli biofilms in the gut can trigger Parkinson's disease in mice. This study emphasizes the possible role of the gut microbiome in modulation (and even initiation) of human neurodegenerative disorders, such as Parkinson's disease. As the CsgA protein was found to accelerate alpha-synuclein (the key amyloidogenic protein in Parkinson's disease) amyloid formation in vitro, this result suggests that also other amyloidogenic proteins from gut bacteria, and even from the diet (such as stable allergenic proteins), may be able to affect human protein conformations and thereby modulate amyloid-related diseases. In this review, we summarize what has been reported in terms of in vitro cross-reactivity studies between alpha-synuclein and other amyloidogenic human and non-human proteins. It becomes clear from the limited data that exist that there is a fine line between acceleration and inhibition, but that cross-reactivity is widespread, and it is more common for other proteins (among the studied cases) to accelerate alpha-synuclein amyloid formation than to block it. It is of high importance to expand investigations of cross-reactivity between amyloidogenic proteins to both reveal underlying mechanisms and links between human diseases, as well as to develop new treatments that may be based on an altered gut microbiome.

Interaction between Copper Chaperone Atox1 and Parkinson's Disease Protein α-Synuclein Includes Metal-Binding Sites and Occurs in Living Cells

Alterations in copper ion homeostasis appear coupled to neurodegenerative disorders, but mechanisms are unknown. The cytoplasmic copper chaperone Atox1 was recently found to inhibit amyloid formation in vitro of α-synuclein, the amyloidogenic protein in Parkinson's disease. As α-synuclein may have copper-dependent functions, and free copper ions promote α-synuclein amyloid formation, it is important to characterize the Atox1 interaction with α-synuclein on a molecular level. Here we applied solution-state nuclear magnetic resonance spectroscopy, with isotopically labeled α-synuclein and Atox1, to define interaction regions in both proteins. The α-synuclein interaction interface includes the whole N-terminal part up to Gln24; in Atox1, residues around the copper-binding cysteines (positions 11-16) are mostly perturbed, but additional effects are also found for residues elsewhere in both proteins. Because α-synuclein is N-terminally acetylated in vivo, we established that Atox1 also inhibits amyloid formation of this variant in vitro, and proximity ligation in human cell lines demonstrated α-synuclein-Atox1 interactions in situ. Thus, this interaction may provide the direct link between copper homeostasis and amyloid formation in vivo.