Copper(II)-induced self-oligomerization of alpha-synuclein

Tuning the Balance between Fibrillation and Oligomerization of α-Synuclein in the Presence of Dopamine

The aggregates of α-synuclein bear a close connection with Parkinson's disease, which is largely characterized by the loss of the dopaminergic neurons. Dopamine promotes the formation of undesirable sodium dodecyl sulfate (SDS)-resistant oligomers of α-synuclein. In this study, we have shown that the inhibition of fibrillation by an additive may not always be the ultimate deciding factor in the context of its potential as a successful additive. Copper promotes the fibrillation of α-synuclein in buffer alone but inhibits the formation of SDS-resistant oligomers in the presence of dopamine. Glycerol, on the other hand, increases the population of such dopamine-mediated SDS-resistant oligomers. We speculate such an effect to be a manifestation of the distinct oxidation pathway of dopamine in the presence of copper.

Fabrication of Protease-Sensitive and Light-Responsive Microcapsules Encompassed with Single Layer of Gold Nanoparticles by Using Self-Assembly Protein of α-Synuclein

A bioapplicable cargo delivery system requires the following characteristics of biocompatibility, in vivo stability, and selective cargo release at target sites. We introduce herein the microcapsules enclosed with a single-layered shell of gold nanoparticles (AuNPs) mutually connected by an amyloidogenic protein of α-synuclein (αS). The microcapsules were fabricated by producing oil(chloroform)-in-water Pickering emulsions of the αS-encapsulated AuNPs and subsequent molecular engagement of the outlying αS molecules, leading to formidable β-sheet formation in the presence of chloroform. The wrinkled skin of microcapsules obtained after evaporation of the internal chloroform also reflects robustness of the protein-protein interaction, which was experimentally confirmed by their rheological stability. For the emulsions loaded with rhodamine 6G, their dye release was demonstrated to be controlled by proteases. Along with their photothermal activity, the AuNP-containing microcapsules and their proteolyzed fragments were therefore suggested to be capable of eliminating aberrant cells in the protease-activated pathologically affected areas. Orthogonal cargo loading was also achieved by encapsulating both hydrophobic and hydrophilic substances either directly dissolved in chloroform or prepackaged in inverted micelles, respectively. Microcapsule's functionality was further expanded by localizing quantum dots, magnetic nanoparticles, and antibodies inside or on the surface of the microcapsules. Taken together, these multimodal AuNP microcapsules are suggested to be an ideal cargo carrier system, which could be employed in not only biomedical theranostic applications as they exhibit structural robustness, specific targeting, triggered release, and photothermal activity but also sensor development in general.

Peculiarities of copper binding to alpha-synuclein

Heavy metals have been implicated as the causative agents for the pathogenesis of the most prevalent neurodegenerative disease. Various mechanisms have been proposed to explain the toxic effects of metals ranging from metal-induced oxidation of protein to metal-induced changes in the protein conformation. Aggregation of a-synuclein is implicated in Parkinson's disease (PD), and various metals, including copper, constitute a prominent group of alpha-synuclein aggregation enhancers. In this study, we have systematically characterized the a-synuclein-Cu21 binding sites and analyzed the possible role of metal binding in a-synuclein fibrillation using a set of biophysical techniques, such as electron paramagnetic resonance (EPR), electron spin-echo envelope modulation (ESEEM), circular dichroism (CD), and size exclusion chromatography (SEC). Our analyses indicated that a-synuclein possesses at least two binding sites for Cu21. We have been able to locate one of the binding sites in the N-terminal region. Furthermore, based on the EPR studies of model peptides and Beta-synuclein, we concluded that the suspected His residue did not appear to participate in strong Cu21 binding.

Role of zinc and copper ions in the pathogenetic mechanisms of Alzheimer's and Parkinson's diseases

Disbalance of zinc (Zn2+) and copper (Cu2+) ions in the central nervous system is involved in the pathogenesis of numerous neurodegenerative disorders such as multisystem atrophy, amyotrophic lateral sclerosis, Creutzfeldt-Jakob disease, Wilson-Konovalov disease, Alzheimer's disease, and Parkinson's disease. Among these, Alzheimer's disease (AD) and Parkinson's disease (PD) are the most frequent age-related neurodegenerative pathologies with disorders in Zn2+ and Cu2+ homeostasis playing a pivotal role in the mechanisms of pathogenesis. In this review we generalized and systematized current literature data concerning this problem. The interactions of Zn2+ and Cu2+ with amyloid precursor protein (APP), β-amyloid (Abeta), tau-protein, metallothioneins, and GSK3β are considered, as well as the role of these interactions in the generation of free radicals in AD and PD. Analysis of the literature suggests that the main factors of AD and PD pathogenesis (oxidative stress, structural disorders and aggregation of proteins, mitochondrial dysfunction, energy deficiency) that initiate a cascade of events resulting finally in the dysfunction of neuronal networks are mediated by the disbalance of Zn2+ and Cu2+.

Catecholamine autotoxicity. Implications for pharmacology and therapeutics of Parkinson disease and related disorders

Several neurodegenerative diseases involve loss of catecholamine neurons-Parkinson disease is a prototypical example. Catecholamine neurons are rare in the nervous system, and why they are vulnerable in PD and related disorders has been mysterious. Accumulating evidence supports the concept of "autotoxicity"-inherent cytotoxicity of catecholamines and their metabolites in the cells in which they are produced. According to the "catecholaldehyde hypothesis" for the pathogenesis of Parkinson disease, long-term increased build-up of 3,4-dihydroxyphenylacetaldehyde (DOPAL), the catecholaldehyde metabolite of dopamine, causes or contributes to the eventual death of dopaminergic neurons. Lewy bodies, a neuropathologic hallmark of PD, contain precipitated alpha-synuclein. Bases for the tendency of alpha-synuclein to precipitate in the cytoplasm of catecholaminergic neurons have also been mysterious. Since DOPAL potently oligomerizes and aggregates alpha-synuclein, the catecholaldehyde hypothesis provides a link between alpha-synucleinopathy and catecholamine neuron loss in Lewy body diseases. The concept developed here is that DOPAL and alpha-synuclein are nodes in a complex nexus of interacting homeostatic systems. Dysfunctions of several processes, including decreased vesicular sequestration of cytoplasmic catecholamines, decreased aldehyde dehydrogenase activity, and oligomerization of alpha-synuclein, lead to conversion from the stability afforded by negative feedback regulation to the instability, degeneration, and system failure caused by induction of positive feedback loops. These dysfunctions result from diverse combinations of genetic predispositions, environmental exposures, stress, and time. The notion of catecholamine autotoxicity has several implications for treatment, disease modification, and prevention. Conversely, disease modification clinical trials would provide key tests of the catecholaldehyde hypothesis.

Protein phosphorylation in neurodegeneration: friend or foe?

Protein misfolding and aggregation is a common hallmark in neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD), and fronto-temporal dementia (FTD). In these disorders, the misfolding and aggregation of specific proteins occurs alongside neuronal degeneration in somewhat specific brain areas, depending on the disorder and the stage of the disease. However, we still do not fully understand the mechanisms governing protein aggregation, and whether this constitutes a protective or detrimental process. In PD, alpha-synuclein (aSyn) forms protein aggregates, known as Lewy bodies, and is phosphorylated at serine 129. Other residues have also been shown to be phosphorylated, but the significance of phosphorylation in the biology and pathophysiology of the protein is still controversial. In AD and in FTD, hyperphosphorylation of tau protein causes its misfolding and aggregation. Again, our understanding of the precise consequences of tau phosphorylation in the biology and pathophysiology of the protein is still limited. Through the use of a variety of model organisms and technical approaches, we are now gaining stronger insight into the effects of phosphorylation in the behavior of these proteins. In this review, we cover recent findings in the field and discuss how targeting phosphorylation events might be used for therapeutic intervention in these devastating diseases of the nervous system.

Antioxidant gene therapy against neuronal cell death

Oxidative stress is a common hallmark of neuronal cell death associated with neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, as well as brain stroke/ischemia and traumatic brain injury. Increased accumulation of reactive species of both oxygen (ROS) and nitrogen (RNS) has been implicated in mitochondrial dysfunction, energy impairment, alterations in metal homeostasis and accumulation of aggregated proteins observed in neurodegenerative disorders, which lead to the activation/modulation of cell death mechanisms that include apoptotic, necrotic and autophagic pathways. Thus, the design of novel antioxidant strategies to selectively target oxidative stress and redox imbalance might represent important therapeutic approaches against neurological disorders. This work reviews the evidence demonstrating the ability of genetically encoded antioxidant systems to selectively counteract neuronal cell loss in neurodegenerative diseases and ischemic brain damage. Because gene therapy approaches to treat inherited and acquired disorders offer many unique advantages over conventional therapeutic approaches, we discussed basic research/clinical evidence and the potential of virus-mediated gene delivery techniques for antioxidant gene therapy.

Divalent metal ions enhance DOPAL-induced oligomerization of alpha-synuclein

Parkinson disease (PD) features profound striatal dopamine depletion and Lewy bodies containing abundant precipitated alpha-synuclein. Mechanisms linking alpha-synucleinopathy with the death of dopamine neurons remain incompletely understood. One such link may be 3,4-dihydroxyphenylacetaldehyde (DOPAL). All of the intra-neuronal metabolism of dopamine passes through DOPAL, which is toxic. DOPAL also potently oligomerizes alpha-synuclein and alpha-synuclein oligomers are thought to be pathogenic in PD. Another implicated factor in PD pathogenesis is metal ions, and alpha-synuclein contains binding sites for these ions. In this study we tested whether divalent metal ions augment DOPAL-induced oligomerization of alpha-synuclein in cell-free system and in PC12 cells conditionally over-expressing alpha-synuclein. Incubation with divalent metal ions augmented DOPAL-induced oligomerization of alpha-synuclein (Cu(2+)>Fe(2+)>Mn(2+)), whereas monovalent Cu(1+) and trivalent Fe(3+) were without effect. Other dopamine metabolites, dopamine itself, and metal ions alone or in combination with dopamine, also had no effect. Antioxidant treatment with ascorbic acid and divalent cation chelation with EDTA attenuated the augmentation by Cu(2+) of DOPAL-induced alpha-synuclein oligomerization. Incubation of PC12 cells with L-DOPA markedly increased intracellular DOPAL content and promoted alpha-synuclein dimerization. Co-incubation with Cu(2+) amplified (p=0.01), while monoamine oxidase inhibition prevented, L-DOPA-related dimerization of alpha-synuclein (p=0.01). We conclude that divalent metal ions augment DOPAL-induced oligomerization of alpha-synuclein. Drugs that interfere with this interaction might constitute a novel approach for future treatment or prevention approaches.

Copper and copper proteins in Parkinson's disease

Copper is a transition metal that has been linked to pathological and beneficial effects in neurodegenerative diseases. In Parkinson's disease, free copper is related to increased oxidative stress, alpha-synuclein oligomerization, and Lewy body formation. Decreased copper along with increased iron has been found in substantia nigra and caudate nucleus of Parkinson's disease patients. Copper influences iron content in the brain through ferroxidase ceruloplasmin activity; therefore decreased protein-bound copper in brain may enhance iron accumulation and the associated oxidative stress. The function of other copper-binding proteins such as Cu/Zn-SOD and metallothioneins is also beneficial to prevent neurodegeneration. Copper may regulate neurotransmission since it is released after neuronal stimulus and the metal is able to modulate the function of NMDA and GABA A receptors. Some of the proteins involved in copper transport are the transporters CTR1, ATP7A, and ATP7B and the chaperone ATOX1. There is limited information about the role of those biomolecules in the pathophysiology of Parkinson's disease; for instance, it is known that CTR1 is decreased in substantia nigra pars compacta in Parkinson's disease and that a mutation in ATP7B could be associated with Parkinson's disease. Regarding copper-related therapies, copper supplementation can represent a plausible alternative, while copper chelation may even aggravate the pathology.

Structural differences between native Hen egg white lysozyme and its fibrils under different environmental conditions

The difference in molecular structure of native HEWL and its fibrils, grown at a pH value near physiological pH 7.4 and at a pH value just above the pI, 10.7 in presence and absence of Cu(II) ions, is discussed. We focus on differences between the molecular structure of the native protein and fibrils using principal component analysis of their Raman spectra. The overlap areas of the scores of each species are used to quantify the difference in the structure of the native HEWL and fibrils in different environments. The overall molecular structures are significantly different for fibrils grown at two pH values. However, in presence of Cu(II) ions, the fibrils have similarities in their molecular structures at these pH environments. Spectral variation within each species, as obtained from the standard deviations of the scores in PCA plots, reveals the variability in the structure within a particular species.

α-Synuclein in Parkinson's disease: pathogenic function and translation into animal models

Parkinson's disease is a common neurodegenerative disease characterised by the loss of dopaminergic neurons in the substantia nigra pars compacta and the formation of α-synuclein aggregates found in Lewy bodies throughout the brain. Several α-synuclein transgenic mouse models have been generated, as well as viral-mediated overexpression of wild-type and mutated α-synuclein to mimic the disease and to delineate the pathogenic pathway of α-synuclein-mediated toxicity and neurodegeneration. In this review, we will recapitulate what we have learned about the function of α-synuclein and α-synuclein-mediated toxicity through studies of transgenic animal models, inducible animal models and viral-based models.

α-Synuclein aggregation and modulating factors

Aggregated a-synuclein is the major component of inclusions in Parkinson's disease and other synucleinopathy brains indicating that a-syn aggregation is associated with the pathogenesis of neurodegenerative disorders. Although the mechanisms underlying a-syn aggregation and toxicity are not fully elucidated, it is clear that a-syn undergoes post-translational modifications and interacts with numerous proteins and other macromolecules, metals, hormones, neurotransmitters, drugs and poisons that can all modulate its aggregation propensity. The current and most recent findings regarding the factors modulating a-syn aggregation process are discussed in detail.

Α-synuclein misfolding and Parkinson's disease

Substantial evidence links α-synuclein, a small highly conserved presynaptic protein with unknown function, to both familial and sporadic Parkinson's disease (PD). α-Synuclein has been identified as the major component of Lewy bodies and Lewy neurites, the characteristic proteinaceous deposits that are the hallmarks of PD. α-Synuclein is a typical intrinsically disordered protein, but can adopt a number of different conformational states depending on conditions and cofactors. These include the helical membrane-bound form, a partially-folded state that is a key intermediate in aggregation and fibrillation, various oligomeric species, and fibrillar and amorphous aggregates. The molecular basis of PD appears to be tightly coupled to the aggregation of α-synuclein and the factors that affect its conformation. This review examines the different aggregation states of α-synuclein, the molecular mechanism of its aggregation, and the influence of environmental and genetic factors on this process.

Redox activity of α-synuclein-Cu is silenced by Zn₇-metallothionein-3

The aggregation of α-synuclein (α-Syn), the major component of intracellular Lewy body inclusions in dopaminergic neurons of the substantia nigra, plays a critical role in the etiology of Parkinson disease (PD). Long-term effects of redox-active transition metals (Cu, Fe) and oxidative chemical imbalance underlie the disease progression and neuronal death. In this work, we provide evidence that a brain metalloprotein, Zn₇-metallothionein-3 (Zn₇MT-3), possesses a dynamic role in controlling aberrant protein-copper interactions in PD. We examined the properties of the α-Syn-Cu(II) complex with regard to molecular oxygen, the biological reducing agent ascorbate, and the neurotransmitter dopamine. The results revealed that under aerobic conditions α-Syn-Cu(II) possesses catalytic oxidase activity. The observed metal-centered redox chemistry significantly promotes the production of hydroxyl radicals and α-Syn oxidation and oligomerization, processes considered critical for cellular toxicity. Moreover, we show that Zn₇MT-3, through Cu(II) removal from the α-Syn-Cu(II) complex, efficiently prevents its deleterious redox activity. We demonstrate that the Cu(II) reduction by thiolate ligands of Zn₇MT-3 and the formation of Cu(I)₄Zn₄MT-3, in which an unusual oxygen-stable Cu(I)₄-thiolate cluster is present, comprise the underlying molecular mechanism by which α-Syn and dopamine oxidation, α-Syn oligomerization, and ROS production are abolished. These studies provide new insights into the bioinorganic chemistry of PD.

Structure and properties of a complex of α-synuclein and a single-domain camelid antibody

The aggregation of the intrinsically disordered protein α-synuclein to form fibrillar amyloid structures is intimately associated with a variety of neurological disorders, most notably Parkinson's disease. The molecular mechanism of α-synuclein aggregation and toxicity is not yet understood in any detail, not least because of the paucity of structural probes through which to study the behavior of such a disordered system. Here, we describe an investigation involving a single-domain camelid antibody, NbSyn2, selected by phage display techniques to bind to α-synuclein, including the exploration of its effects on the in vitro aggregation of the protein under a variety of conditions. We show using isothermal calorimetric methods that NbSyn2 binds specifically to monomeric α-synuclein with nanomolar affinity and by means of NMR spectroscopy that it interacts with the four C-terminal residues of the protein. This latter finding is confirmed by the determination of a crystal structure of NbSyn2 bound to a peptide encompassing the nine C-terminal residues of α-synuclein. The NbSyn2:α-synuclein interaction is mediated mainly by side-chain interactions while water molecules cross-link the main-chain atoms of α-synuclein to atoms of NbSyn2, a feature we believe could be important in intrinsically disordered protein interactions more generally. The aggregation behavior of α-synuclein at physiological pH, including the morphology of the resulting fibrillar structures, is remarkably unaffected by the presence of NbSyn2 and indeed we show that NbSyn2 binds strongly to the aggregated as well as to the soluble forms of α-synuclein. These results give strong support to the conjecture that the C-terminal region of the protein is not directly involved in the mechanism of aggregation and suggest that binding of NbSyn2 could be a useful probe for the identification of α-synuclein aggregation in vitro and possibly in vivo.

Role of post-translational modifications in modulating the structure, function and toxicity of alpha-synuclein: implications for Parkinson's disease pathogenesis and therapies

A better understanding of the molecular and cellular determinants that influence the pathology of Parkinson's disease (PD) is essential for developing effective diagnostic, preventative and therapeutic strategies to treat this devastating disease. A number of post-translational modifications to alpha-syn are present within the Lewy bodies in the brains of affected patients and transgenic models of PD and related disorders. However, whether disease-associated alpha-syn post-translational modifications promote or inhibit alpha-syn aggregation and neurotoxicity in vivo remains unknown. Herein, we summarize and discuss the major disease-associated post-translational modifications (phosphorylation, truncation and ubiquitination) and present our current understanding of the effect of these modifications on alpha-syn aggregation and toxicity. Elucidating the molecular mechanisms underlying post-translation modifications of alpha-syn and the consequences of such modifications on the biochemical, structural, aggregation and toxic properties of the protein is essential for unravelling the molecular basis of its function(s) in health and disease. Furthermore, the identification of the natural enzymes involved in regulating the post-translational modifications of alpha-synuclein will yield novel and more tractable therapeutic targets to treat PD and related synucleinopathies.

Protein-metal interactions of calmodulin and alpha-synuclein monitored by selective noncovalent adduct protein probing mass spectrometry

The metal binding properties of proteins are biologically significant, particularly in relationship to the molecular origins of disease and the discovery of therapeutic pharmaceutical treatments. Herein, we demonstrate that selective noncovalent adduct protein probing mass spectrometry (SNAPP-MS) is a sensitive technique to investigate the structural effects of protein-metal interactions. We utilize specific, noncovalent interactions between 18-crown-6 ether (18C6) and lysine to probe protein structure in the presence and absence of metal ions. Application of SNAPP-MS to the calmodulin-Ca2+ system demonstrates that changes in protein structure are reflected in a substantial change in the number and intensity of 18C6s, which bind to the protein as observed by MS. In this manner, SNAPP is demonstrated to be a sensitive technique for monitoring ligand-induced conformational rearrangements in proteins. In addition, SNAPP is well-suited to examine the properties of natively unfolded proteins, where structural changes are more difficult to detect by other methods. For example, alpha-synuclein is a protein associated in the pathology of Parkinson's disease, which is known to aggregate more rapidly in the presence of Al3+ and Cu2+. The 18C6 SNAPP distributions for alpha-synuclein change dramatically in the presence of 3 microM Al3+, revealing that Al3+ binding causes a significant change in the conformational dynamics of the monomeric form of this disordered protein. In contrast, binding of Cu2+ does not induce a significant shift in 18C6 binding, suggesting that noteworthy structural reorganizations at the monomeric level are minimal. These results are consistent with the idea that the metal-induced aggregation caused by Al3+ and Cu2+ proceed by independent pathways.

Mathematical approach to understand the kinetics of alpha-synuclein aggregation: relevance to Parkinson's disease

alpha-Synuclein aggregation is a hallmark pathological feature in Parkinson's disease (PD). The conversion of alpha-synuclein from soluble monomer to insoluble aggregates through the toxic oligomeric intermediates underlie the neurodegeneration associated with PD. Redox active metal ions such as iron (Fe) and copper (Cu) are known to enhance alpha-synuclein fibrillogenesis. In the present study, we have implemented mathematical approach to monitor the kinetics of aggregation of alpha-synuclein nucleation and elongation constants based on fluorescence studies. In this pretext, we have implemented mathematical simulations like self and absolute analysis. The mathematical model discussed in this paper is the first of its kind and might prove useful for predicting the drug intervention time to prevent alpha-synuclein aggregation and has future clinical application.

alpha-Synuclein enhances secretion and toxicity of amyloid beta peptides in PC12 cells

alpha-Synuclein is the fundamental component of Lewy bodies which occur in the brain of 60% of sporadic and familial Alzheimer's disease patients. Moreover, a proteolytic fragment of alpha-synuclein, the so-called non-amyloid component of Alzheimer's disease amyloid, was found to be an integral part of Alzheimer's dementia related plaques. However, the role of alpha-synuclein in pathomechanism of Alzheimer's disease remains elusive. In particular, the relationship between alpha-synuclein and amyloid beta is unknown. In the present study we showed the involvement of alpha-synuclein in amyloid beta secretion and in the mechanism of amyloid beta evoked mitochondria dysfunction and cell death. Rat pheochromocytoma PC12 cells transfected with amyloid beta precursor protein bearing Swedish double mutation (APPsw) and control PC12 cells transfected with empty vector were used in this study. alpha-Synuclein (10microM) was found to increase by twofold amyloid beta secretion from control and APPsw PC12 cells. Moreover, alpha-synuclein decreased the viability of PC12 cells by about 50% and potentiated amyloid beta toxicity leading to mitochondrial dysfunction and caspase-dependent programmed cell death. Inhibitor of caspase-3 (Z-DEVD-FMK, 100microM), and a mitochondrial permeability transition pore blocker, cyclosporine A (2microM) protected PC12 cells against alpha-synuclein or amyloid beta evoked cell death. In contrast Z-DEVD-FMK and cyclosporine A were ineffective in APPsw cells containing elevated amount of amyloid beta treated with alpha-synuclein. It was found that the inhibition of neuronal and inducible nitric oxide synthase reversed the toxic effect of alpha-synuclein in control but not in APPsw cells. Our results indicate that alpha-synuclein enhances the release and toxicity of amyloid beta leading to nitric oxide mediated irreversible mitochondria dysfunction and caspase-dependent programmed cell death.

Copper- and iron-induced differential fibril formation in α-synuclein: TEM study

alpha-Synuclein filaments are the central component of intracytoplasmic inclusion bodies characteristic of Parkinson's disease (PD) and related disorders. Metals are the significant etiological factors in PD, and their interaction with alpha-synuclein affect dramatically the kinetics of fibrillation. Currently, we have investigated the influence of Cu(II) and Fe(III) on alpha-synuclein fibril formation. Cu(II) and Fe(III) selectively and differentially induced the formation of discrete alpha-synuclein fibrillar species. Transmission electron microscopy was used to monitor the aggregation state of alpha-synuclein (wild-type, A30P, A53T, and E46K) after 60h with stirring at 37 degrees C in the presence and absence of metal ions. Cu(II) has induced thin long network-like fibrils with the wild-type of alpha-synuclein, while the mutant, showed amorphous aggregates with no fibrillar forms. Fe(III) induced short and thick fibrils with both wild and mutant forms and were similar to alpha-synuclein fibrils incubated without metal ion. The present study illustrates the metal-specific fibril morphology, and has relevance in understanding the role of metals in neurodegeneration.

Neuropathology, biochemistry, and biophysics of alpha-synuclein aggregation

Aggregation of alpha-synuclein, an abundant and conserved pre-synaptic brain protein, is implicated as a critical factor in several neurodegenerative diseases. These diseases, known as synucleinopathies, include Parkinson's disease, dementia with Lewy bodies (LBs), diffuse LB disease, the LB variant of Alzheimer's disease, multiple system atrophy, and neurodegeneration with brain iron accumulation type I. Although the precise nature of in vivoalpha-synuclein function remains elusive, considerable knowledge has been accumulated about its structural properties and conformational behavior. alpha-Synuclein is a typical natively unfolded protein. It is characterized by the lack of rigid, well-defined, 3-D structure and possesses remarkable conformational plasticity. The structure of this protein depends dramatically on its environment and it accommodates a number of unrelated conformations. This paper provides an overview of the biochemistry, biophysics, and neuropathology of alpha-synuclein aggregation.

Interactions between metals and alpha-synuclein--function or artefact?

alpha-synuclein is one of a family of proteins whose function remains unknown. This protein has become linked to a number of neurodegenerative disease although its potential causative role in these diseases remains mysterious. In diseases such as Parkinson's disease and Lewy body dementias, alpha-synuclein becomes deposited in aggregates termed Lewy bodies. Also, some inherited forms of Parkinson's diseases are linked to mutations in the gene for alpha-synuclein. Studies have mostly focussed on what causes the aggregation of the protein but, like many amyloidogenic proteins associated with a neurodegenerative disorder, this protein has now been suggested to bind copper. This finding is currently controversial. This review examines the evidence that alpha-synuclein is a copper binding protein and discusses whether this has any significance in determining the function of the protein or whether copper binding is at all necessary for aggregation.

Mechanisms of cholinesterase inhibition by inorganic mercury

The poorly known mechanism of inhibition of cholinesterases by inorganic mercury (HgCl2) has been studied with a view to using these enzymes as biomarkers or as biological components of biosensors to survey polluted areas. The inhibition of a variety of cholinesterases by HgCl2 was investigated by kinetic studies, X-ray crystallography, and dynamic light scattering. Our results show that when a free sensitive sulfhydryl group is present in the enzyme, as in Torpedo californica acetylcholinesterase, inhibition is irreversible and follows pseudo-first-order kinetics that are completed within 1 h in the micromolar range. When the free sulfhydryl group is not sensitive to mercury (Drosophila melanogaster acetylcholinesterase and human butyrylcholinesterase) or is otherwise absent (Electrophorus electricus acetylcholinesterase), then inhibition occurs in the millimolar range. Inhibition follows a slow binding model, with successive binding of two mercury ions to the enzyme surface. Binding of mercury ions has several consequences: reversible inhibition, enzyme denaturation, and protein aggregation, protecting the enzyme from denaturation. Mercury-induced inactivation of cholinesterases is thus a rather complex process. Our results indicate that among the various cholinesterases that we have studied, only Torpedo californica acetylcholinesterase is suitable for mercury detection using biosensors, and that a careful study of cholinesterase inhibition in a species is a prerequisite before using it as a biomarker to survey mercury in the environment.

Copper ions disrupt dopamine metabolism via inhibition of V-H+-ATPase: a possible contributing factor to neurotoxicity

The involvement of copper in the pathophysiology of neurodegeneration has been well documented but is not fully understood. Commonly, the effects are attributed to increased reactive oxygen species (ROS) production due to inherent redox properties of copper ions. Here we show copper can have physiological effects distinct from direct ROS production. First, we show that extragranular free copper inhibits the vesicular H(+)-ATPase of resealed chromaffin granule ghosts. Extragranular ascorbate potentiates this inhibition. The inhibition is mixed type with K(is) = 6.8 +/- 2.8 micromol/L and K(ii) = 3.8 +/- 0.6 micromol/L, with respect to ATP. Second, extracellular copper causes an inhibition of the generation of a pH-gradient and rapid dissipation of pre-generated pH and catecholamine gradients. Copper chelators and the ss-amyloid peptide 1-42 were found to effectively prevent the inhibition. The inhibition is reversible and time-independent suggesting the effects of extracellular copper on H(+)-ATPase is direct, and not due to ROS. The physiological significance of these observations was shown by the demonstration that extracellular copper causes a dramatic perturbation of dopamine metabolism in SH-SY5Y cells. Thus, we propose that the direct inhibition of the vesicular H(+)-ATPase may also contribute to the neurotoxic effects of copper.

Alpha-synuclein in Lewy body disease and Alzheimer's disease

Alzheimer's disease (AD) and Lewy body disease (LBD) are the most common causes of dementia in the elderly population. Previous studies have shown that cognitive alterations in these disorders are associated with synaptic loss. Injury and loss of synapses might be associated with altered function of synaptic proteins. Among them, recent studies have shown that abnormal aggregation and accumulation of synaptic proteins, such as alpha-synuclein, might be associated with plaque formation in AD and Lewy body formation in LBD. Further reinforcing the hypothesis that alpha-synuclein plays a major role in the pathogenesis of these disorders, recent work has shown that mutations that alter the conformation of this molecule are associated with familial forms of Parkinson's disease. The mechanisms by which altered function or aggregation of alpha-synuclein might lead to neurodegeneration are not completely clear; however, new evidence points to a potential role for this molecule in synaptic damage and neurotoxicity via amyloid-like fibril formation and mitochondrial dysfunction. In this manuscript we review the data linking alpha-synuclein to the pathogenesis of AD and LBD.

Free radical-mediated neurotoxicity may be caused by inhibition of mitochondrial dehydrogenases in vitro and in vivo

We previously demonstrated that copper facilitated the formation of reactive oxygen species, and inhibited pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase in vitro and in animal models of Wilson's disease in vivo. However, direct Cu(2+) toxicity has only been demonstrated for Wilson's disease. We now hypothesize that inhibition of these mitochondrial dehydrogenases might also contribute to many other injuries and disorders that are reactive oxygen species-mediated. We have modeled reactive oxygen species-mediated injuries using inducers of reactive oxygen species such as hydrogen peroxide, ethacrynic acid or menadione, or another redox active metal (Cd(2+)). Here we demonstrated that these toxic exposures were accompanied by an early marked reduction in both pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase activities, followed by a decrease in neuronal mitochondrial transmembrane potential and ATP, prior to murine cortical neuronal death. Thiamine (6 mM), and dihydrolipoic acid (50 microM), required cofactors for pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase (thiamine as thiamine pyrophosphate), attenuated the reactive oxygen species-induced reductions in these enzyme activities, as well as subsequent loss of mitochondrial transmembrane potential and ATP, and neuronal death. We next tested the effect of thiamine supplementation on an in vivo model of reactive oxygen species-mediated injury, transient middle cerebral artery occlusion, and reperfusion in rats. Oral or i.p. thiamine administration reduced the middle cerebral artery occlusion-induced infarct. These data suggest that reactive oxygen species-induced neuronal death may be caused in part by reactive oxygen species-mediated inhibition of pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase in vitro and in vivo, and that thiamine or dihydrolipoic acid may constitute potential therapeutic agents not just against Cu(2+) neurotoxicity, but may reduce neuronal degeneration in the broader range of diseases mediated by free radical stress.

Preparation of alpha-synuclein fibrils for solid-state NMR: expression, purification, and incubation of wild-type and mutant forms

We report the expression and purification of alpha-synuclein, a protein implicated in Parkinson's disease, from isotopically (13C, 15N) labeled bacterial growth media, as required for solid-state NMR structural studies. Expression from Escherichia coli (BL21(DE3)) was performed with a protocol optimized for time efficiency and yield. Chemical lysis, crude purification by ammonium sulfate precipitation, and two chromatography steps (hydrophobic interaction and size exclusion) yield 30-35 mg/L of growth medium. Purity is confirmed by gel electrophoresis and mass spectrometry. Furthermore, we demonstrate reproducible fibril growth by control of environmental incubation conditions. Highly resolved multidimensional solid-state NMR spectra indicate microscopic order throughout the majority of the AS fibril structure. The number of signals and intensities of well-resolved residue types (Thr, Ser, Ala, Gly, Val, and Ile) are consistent with a single conformation, which is reproducibly prepared by seeding consecutive preparations. Variations in the fibril growth rates and structural polymorphisms exhibited in the solid-state NMR spectra are minimized by careful control of incubation conditions.

NMR mapping of copper binding sites in alpha-synuclein

Copper binding to the Parkinson disease-linked protein alpha-synuclein (aS) has been shown to accelerate its oligomerization in vitro and may therefore play a role in aS-mediated pathology in vivo. We use NMR spectroscopy to identify a number of independent copper binding sites in both the lipid-binding N-terminal domain and the highly acidic C-terminal domain of aS. Most of the sites appear to involve negatively charged amino acid side chains, but binding is also observed to the sole histidine residue located at position 50 and to the N-terminal amino group. Both the N-terminal and the histidine sites, as well as the sites in the C-terminal tail, can also bind copper in the more highly structured conformation adopted by aS upon binding to detergent micelles or lipid vesicles. There is no evidence for the formation of any sites requiring long-range order in the protein.