Alpha-synuclein has structural and functional similarities to small heat shock proteins

Saccharomyces cerevisiae as a Model for Studying Human Neurodegenerative Disorders: Viral Capsid Protein Expression

In this article, we briefly describe human neurodegenerative diseases (NDs) and the experimental models used to study them. The main focus is the yeast Saccharomyces cerevisiae as an experimental model used to study neurodegenerative processes. We review recent experimental data on the aggregation of human neurodegenerative disease-related proteins in yeast cells. In addition, we describe the results of studies that were designed to investigate the molecular mechanisms that underlie the aggregation of reporter proteins. The advantages and disadvantages of the experimental approaches that are currently used to study the formation of protein aggregates are described. Special attention is given to the similarity between aggregates that form as a result of protein misfolding and viral factories-special structural formations in which viral particles are formed inside virus-infected cells. A separate part of the review is devoted to our previously published study on the formation of aggregates upon expression of the insect densovirus capsid protein in yeast cells. Based on the reviewed results of studies on NDs and related protein aggregation, as well as viral protein aggregation, a new experimental model system for the study of human NDs is proposed. The core of the proposed system is a comparative transcriptomic analysis of changes in signaling pathways during the expression of viral capsid proteins in yeast cells.

Single point mutations at the S129 residue of α-synuclein and their effect on structure, aggregation, and neurotoxicity

Parkinson's disease is an age-related neurological disorder, and the pathology of the disease is linked to different types of aggregates of α-synuclein or alpha-synuclein (aS), which is an intrinsically disordered protein. The C-terminal domain (residues 96-140) of the protein is highly fluctuating and possesses random/disordered coil conformation. Thus, the region plays a significant role in the protein's solubility and stability by an interaction with other parts of the protein. In the current investigation, we examined the structure and aggregation behavior of two artificial single point mutations at a C-terminal residue at position 129 that represent a serine residue in the wild-type human aS (wt aS). Circular Dichroism (CD) and Raman spectroscopy were performed to analyse the secondary structure of the mutated proteins and compare it to the wt aS. Thioflavin T assay and atomic force microscopy imaging helped in understanding the aggregation kinetics and type of aggregates formed. Finally, the cytotoxicity assay gave an idea about the toxicity of the aggregates formed at different stages of incubation due to mutations. Compared to wt aS, the mutants S129A and S129W imparted structural stability and showed enhanced propensity toward the α-helical secondary structure. CD analysis showed proclivity of the mutant proteins toward α-helical conformation. The enhancement of α-helical propensity lengthened the lag phase of fibril formation. The growth rate of β-sheet-rich fibrillation was also reduced. Cytotoxicity tests on SH-SY5Y neuronal cell lines established that the S129A and S129W mutants and their aggregates were potentially less toxic than wt aS. The average survivability rate was ∼40% for cells treated with oligomers (presumably formed after 24 h of incubation of the freshly prepared monomeric protein solution) produced from wt aS and ∼80% for cells treated with oligomers obtained from mutant proteins. The relative structural stability with α-helical propensity of the mutants could be a plausible reason for their slow rate of oligomerization and fibrillation, and this was also the possible reason for reduced toxicity to neuronal cells.

Differential interactions of α-synuclein conformers affect refolding and activity of proteins

The accumulation of protein aggregates as intracellular inclusions interferes with cellular protein homeostasis leading to protein aggregation diseases. Protein aggregation results in the formation of several protein conformers including oligomers and fibrils, where each conformer has its own structural characteristic and proteotoxic potential. The present study explores the effect of alpha-synuclein (α-syn) conformers on the activity and spontaneous refolding of firefly luciferase. Of the different conformers, α-syn monomers delayed the inactivation of luciferase under thermal stress conditions and enhanced the spontaneous refolding of luciferase. In contrast, the α-syn oligomers and fibrils adversely affected luciferase activity and refolding, where the oligomers inhibited spontaneous refolding, whereas a pronounced effect on the inactivation of native luciferase was observed in the case of fibrils. These results indicate that the oligomers and fibrils of α-syn interfere with the refolding of luciferase and promote its misfolding and aggregation. The study reveals the differential propensities of various conformers of a pathologically relevant protein in causing inactivation, structural modifications and misfolding of other proteins, consequently resulting in altered protein homeostasis.

Neurons and Glia Interplay in α-Synucleinopathies

Accumulation of the neuronal presynaptic protein alpha-synuclein within proteinaceous inclusions represents the key histophathological hallmark of a spectrum of neurodegenerative disorders, referred to by the umbrella term a-synucleinopathies. Even though alpha-synuclein is expressed predominantly in neurons, pathological aggregates of the protein are also found in the glial cells of the brain. In Parkinson's disease and dementia with Lewy bodies, alpha-synuclein accumulates mainly in neurons forming the Lewy bodies and Lewy neurites, whereas in multiple system atrophy, the protein aggregates mostly in the glial cytoplasmic inclusions within oligodendrocytes. In addition, astrogliosis and microgliosis are found in the synucleinopathy brains, whereas both astrocytes and microglia internalize alpha-synuclein and contribute to the spread of pathology. The mechanisms underlying the pathological accumulation of alpha-synuclein in glial cells that under physiological conditions express low to non-detectable levels of the protein are an area of intense research. Undoubtedly, the presence of aggregated alpha-synuclein can disrupt glial function in general and can contribute to neurodegeneration through numerous pathways. Herein, we summarize the current knowledge on the role of alpha-synuclein in both neurons and glia, highlighting the contribution of the neuron-glia connectome in the disease initiation and progression, which may represent potential therapeutic target for a-synucleinopathies.

The Role of α-Synuclein in Methamphetamine-Induced Neurotoxicity

Methamphetamine (METH), a highly addictive psychostimulant, is the second most widely used illicit drug. METH produces damage dopamine neurons and apoptosis via multiple inter-regulating mechanisms, including dopamine overload, hyperthermia, oxidative stress, mitochondria dysfunction, endoplasmic reticulum stress, protein degradation system dysfunction, and neuroinflammation. Increasing evidence suggests that chronic METH abuse is associated with neurodegenerative changes in the human brain and an increased risk of Parkinson's disease (PD). METH use and PD may share some common steps in causing neurotoxicity. Accumulation of α-synuclein, a presynaptic protein, is the pathological hallmark of PD. Intriguingly, α-synuclein upregulation and aggregation are also found in dopaminergic neurons in the substantia nigra in chronic METH users. This suggests α-synuclein may play a role in METH-induced neurotoxicity. The mechanism of α-synuclein cytotoxicity in PD has attracted considerable attention; however, how α-synuclein affects METH-induced neurotoxicity has not been reviewed. In this review, we summarize the relationship between METH use and PD, interdependent mechanisms that are involved in METH-induced neurotoxicity and the significance of α-synuclein upregulation in response to METH use. The identification of α-synuclein overexpression and aggregation as a contributor to METH-induced neurotoxicity may provide a novel therapeutic target for the treatment of the deleterious effect of this drug and drug addiction.

Prion and Prion-Like Protein Strains: Deciphering the Molecular Basis of Heterogeneity in Neurodegeneration

Increasing evidence suggests that neurodegenerative disorders share a common pathogenic feature: the presence of deposits of misfolded proteins with altered physicochemical properties in the Central Nervous System. Despite a lack of infectivity, experimental data show that the replication and propagation of neurodegenerative disease-related proteins including amyloid-β (Aβ), tau, α-synuclein and the transactive response DNA-binding protein of 43 kDa (TDP-43) share a similar pathological mechanism with prions. These observations have led to the terminology of “prion-like” to distinguish between conditions with noninfectious characteristics but similarities with the prion replication and propagation process. Prions are considered to adapt their conformation to changes in the context of the environment of replication. This process is known as either prion selection or adaptation, where a distinct conformer present in the initial prion population with higher propensity to propagate in the new environment is able to prevail over the others during the replication process. In the last years, many studies have shown that prion-like proteins share not only the prion replication paradigm but also the specific ability to aggregate in different conformations, i.e., strains, with relevant clinical, diagnostic and therapeutic implications. This review focuses on the molecular basis of the strain phenomenon in prion and prion-like proteins.

Could α-Synuclein Modulation of Insulin and Dopamine Identify a Novel Link Between Parkinson's Disease and Diabetes as Well as Potential Therapies?

Characterizing the normal function(s) of the protein α-Synuclein (aSyn) has the potential to illuminate links between Parkinson’s disease (PD) and diabetes and also point the way toward new therapies for these disorders. Here we provide a perspective for consideration based on our discovery that aSyn normally acts to inhibit insulin secretion from pancreatic β-cells by interacting with the Kir6.2 subunit of the ATP-sensitive potassium channel (K-ATP). It is also known that K-ATP channels act to inhibit brain dopamine secretion, and we have also shown that aSyn is a normal inhibitor of dopamine synthesis. The finding, that aSyn modulates Kir6.2 and other proteins involved in dopamine and insulin secretion, suggests that aSyn interacting proteins may be negatively impacted when aSyn aggregates inside cells, whether in brain or pancreas. Furthermore, identifying therapies for PD that can counteract dysfunction found in diabetes, would be highly beneficial. One such compound may be the multiple sclerosis drug, FTY720, which like aSyn can stimulate the activity of the catalytic subunit of protein phosphatase 2A (PP2Ac) as well as insulin secretion. In aging aSyn transgenic mice given long term oral FTY720, the mice had reduced aSyn pathology and increased levels of the protective molecule, brain derived neurotrophic factor (BDNF) (Vidal-Martinez et al., 2016). In collaboration with medicinal chemists, we made two non-immunosuppressive FTY720s that also enhance PP2Ac activity, and BDNF expression (Vargas-Medrano et al., 2014; Enoru et al., 2016; Segura-Ulate et al., 2017a). FTY720 and our novel FTY720-based-derivatives, may thus have therapeutic potential for both diabetes and PD.

Cell Biology and Pathophysiology of α-Synuclein

α-Synuclein is an abundant neuronal protein that is highly enriched in presynaptic nerve terminals. Genetics and neuropathology studies link α-synuclein to Parkinson's disease (PD) and other neurodegenerative disorders. Accumulation of misfolded oligomers and larger aggregates of α-synuclein defines multiple neurodegenerative diseases called synucleinopathies, but the mechanisms by which α-synuclein acts in neurodegeneration are unknown. Moreover, the normal cellular function of α-synuclein remains debated. In this perspective, we review the structural characteristics of α-synuclein, its developmental expression pattern, its cellular and subcellular localization, and its function in neurons. We also discuss recent progress on secretion of α-synuclein, which may contribute to its interneuronal spread in a prion-like fashion, and describe the neurotoxic effects of α-synuclein that are thought to be responsible for its role in neurodegeneration.

An intrinsically disordered domain in Polaribacter irgensii KOPRI 22228 CspB confers extraordinary freeze-tolerance

Organisms living in extremely cold environments possess mechanisms to survive low temperatures. Among the known cold-induced genes, cold-shock proteins (Csps) are the most prominent. A csp-homologous gene, cspB_Pi, has been cloned from the Arctic bacterium Polaribacter irgensii KOPRI 22228, and overexpression of this gene greatly increased the freezing tolerance of its host. This protein consists of a unique N-terminal domain and a well conserved C-terminal cold shock domain. To elucidate the detailed mechanisms involved in the extraordinary freeze-tolerance conferred by CspB_Pi, we identified the responsible domain by mutational analysis. Changes of residues in the cold shock domain that are crucial for binding RNA or single-stranded DNA did not impair the ability of the host to survive freezing stress. All domain-shuffled CspB_Pi variants containing the N-terminal domain retained the ability to confer superior freeze-tolerance. Slow electrophoretic mobility and far-UV circular dichroism spectra of the N-terminal domain suggested an intrinsically disordered structure for this region. The N-terminal domain also bound to lipid vesicles in vitro. This lipid vesicle binding characteristic is shared with other intrinsically disordered proteins, such as α-synuclein and plant dehydrins, known to confer cold-tolerance when overexpressed, suggesting a mechanism for cold-survival through membrane binding.

Age-Related Changes of 14-3-3 Isoforms in Midbrain of A53T-SNCA Overexpressing Mice

BACKGROUND

Parkinson's disease (PD) is characterized by loss of midbrain dopaminergic neurons, which are affected by cytoplasmic inclusions, named Lewy pathology. The main component is alpha-synuclein (SNCA), a protein modulating SNARE-complex dependent neurotransmission. SNCA mutations trigger dominantly inherited PD variants and sporadic cases of PD via aggregation and transmission. SNCA and isoforms of the 14-3-3 family show sequence homology, protein interaction and joint aggregation, so 14-3-3 s may be key molecules of pathogenesis.

OBJECTIVE

We aimed to identify the relevant isoforms in midbrain and to distinguish for the first time the changes that occur very early versus those that progress with pathology.

METHODS

We assessed expression of the 14-3-3 family with quantitative RT-PCR and immunoblots of differential solubility fractions in mice with A53T-SNCA overexpression longitudinally at different ages.

RESULTS

Transcript levels showed reductions at age 3 months with increases at later ages for the beta, eta and zeta isoforms. Protein levels at age 3 months exhibited a concordant reduction only for beta, while increased insolubility was observed for epsilon and zeta. At age 18 months only the reduction of 14-3-3 beta protein remained significant. Thus, the toxic gain-of-function of alpha-synuclein leads to early transitory alterations of several 14-3-3 isoforms. When the levels of soluble 14-3-3 proteins become apparently normal during later life, increasing amounts of beta, eta and zeta mRNA are produced, possibly to compensate for protein insolubility and aggregation in a SNCA/14-3-3 complex.

CONCLUSIONS

These data may contribute to identify key molecular events that reflect Parkinson's disease risk and progression.

Alpha-synuclein structure, functions, and interactions

At present, when a clinical diagnosis of Parkinson's disease (PD) is made, serious damage has already been done to nerve cells of the substantia nigra pars compacta. The diagnosis of PD in its earlier stages, before this irreversible damage, would be of enormous benefit for future treatment strategies designed to slow or halt the progression of this disease that possibly prevents accumulation of toxic aggregates. As a molecular biomarker for the detection of PD in its earlier stages, alpha-synuclein (α-syn), which is a key component of Lewy bodies, in which it is found in an aggregated and fibrillar form, has attracted considerable attention. Here, α-syn is reviewed in details.

The Synaptic Function of α-Synuclein

α-Synuclein is an abundant neuronal protein which localizes predominantly to presynaptic terminals, and is strongly linked genetically and pathologically to Parkinson's disease and other neurodegenerative diseases. While the accumulation of α-synuclein in the form of misfolded oligomers and large aggregates defines multiple neurodegenerative diseases called "synucleinopathies", its cellular function has remained largely unclear, and is the subject of intense investigation. In this review, I focus on the structural characteristics of α-synuclein, its cellular and subcellular localization, and discuss how this relates to its function in neurons, in particular at the neuronal synapse.

The crystal structure of Giardia duodenalis 14-3-3 in the apo form: when protein post-translational modifications make the difference

The 14-3-3s are a family of dimeric evolutionary conserved pSer/pThr binding proteins that play a key role in multiple biological processes by interacting with a plethora of client proteins. Giardia duodenalis is a flagellated protozoan that affects millions of people worldwide causing an acute and chronic diarrheal disease. The single giardial 14-3-3 isoform (g14-3-3), unique in the 14-3-3 family, needs the constitutive phosphorylation of Thr214 and the polyglycylation of its C-terminus to be fully functional in vivo. Alteration of the phosphorylation and polyglycylation status affects the parasite differentiation into the cyst stage. To further investigate the role of these post-translational modifications, the crystal structure of the g14-3-3 was solved in the unmodified apo form. Oligomers of g14-3-3 were observed due to domain swapping events at the protein C-terminus. The formation of filaments was supported by TEM. Mutational analysis, in combination with native PAGE and chemical cross-linking, proved that polyglycylation prevents oligomerization. In silico phosphorylation and molecular dynamics simulations supported a structural role for the phosphorylation of Thr214 in promoting target binding. Our findings highlight unique structural features of g14-3-3 opening novel perspectives on the evolutionary history of this protein family and envisaging the possibility to develop anti-giardial drugs targeting g14-3-3.

Evolutionary aspects of the synuclein super-family and sub-families based on large-scale phylogenetic and group-discrimination analysis

Over the last decade, many genetic studies have suggested that the synucleins, which are small, natively unfolded proteins, are closely related to Parkinson's disease and cancer. Less is known about the molecular basis of this role. A comprehensive analysis of the evolutionary path of the synuclein protein family may reveal the relationship between evolutionarily conserved residues and protein function or structure. The phylogeny of 252 unique synuclein sequences from 73 organisms suggests that gamma-synuclein is the common ancestor of alpha- and beta-synuclein. Although all three sub-families remain highly conserved, especially at the N-terminal, nearly 15% of the residues in each sub family clearly diverged during evolution, providing crucial guidance for investigations of the different properties of the members of the superfamily. His50 is found to be an alpha-specific conserved residue (91%) and, based on mutagenesis, evolutionarily developed a secondary copper binding site in the alpha synuclein family. Surprisingly, this site is located between two well-known polymorphisms of alpha-synuclein, E46K and A53T, which are linked to early-onset Parkinson's disease, suggesting that the mutation-induced impairment of copper binding could be a mechanism responsible for alpha-synuclein aggregation.

Α-synuclein and β-synuclein enhance secretion protein production in baculovirus expression vector system

The baculovirus expression vector system (BEVS) is widely used as a tool for expressing of recombinant proteins in insect cells or larvae. However, the expression level of secretion pathway proteins is often lower than that of cytosolic and nucleus proteins. Thus, we attempted to improve production of secreted proteins by using a secretory alkaline phosphatase-EGFP fusion protein (SEFP)-based bi-cistronic baculovirus vector to identify chaperones that have potential on boosting secreted protein production. As co-expressed SEFP with a chaperone, calreticulin (CALR), it was found that the secreted SEFP enzyme activity can be boosted up to twofold. This result demonstrated the SEFP-based bi-cistronic approach can be used to identify the genes that can enhance secretion protein production in BEVS. Thus, the chaperone activity of α-synuclein (α-syn) and β-synuclein (β-syn) was evaluated in cells co-expressed with SEFP and compared that with CALR by analyzing localization, alkaline phosphatase enzyme activity, and mRNA expression levels of SEFP. Our results showed that SEFP enzyme activity from cells co-expressed with both synuclein proteins can be enhanced up to 2.3-fold and this increment was better than that caused by CALR. Moreover, this enhancement might arise from the transcription enhancement or higher RNA stability. By this novel approach, we provided evidences that α- and β-syn can enhance secretion proteins production in BEVS.

Increased expression of α-synuclein by SNCA duplication is associated with resistance to toxic stimuli

Duplication of alpha-synuclein gene (SNCA) is a recognized cause of Parkinson's disease (PD). However, the penetrance in families with SNCA duplication is as low as 30%, indicating that factors other than the SNCA gene dosage have an important role in neuronal death. In this study, using lymphoblastoid cell lines (LCLs) derived from a parkinsonian kindred with SNCA duplication, we examined whether there is difference in (1) the level of SNCA mRNA and protein expression and cell viability and (2) the vulnerability to various insults relevant to PD between a patient, asymptomatic carrier, and unaffected control. Expression of SNCA mRNA and protein increased in the LCLs from subjects with SNCA gene duplication, irrespective of the disease status. In the absence of treatment, LCLs from the patient and carrier showed decreased viability compared with the LCL from the control. The LCL from the patient also showed decreased viability compared to the carrier. When susceptibility to various insults including lactacystin, dexamethasone, 3-methyladenine, H(2)O(2), and rotenone was examined, surprisingly, the LCL from the patient was more resistant than the LCL from the control to all agents except for lactacystin. This study shows that both intrinsic and extrinsic factors and their interaction have important roles in cell death and in the development of PD and further indicates that the relationship between cell death and the level of alpha-synuclein may be more complicated than previously thought.

14-3-3 proteins and regulation of cytoskeleton

The proteins of the 14-3-3 family are universal adapters participating in multiple processes running in the cell. We describe the structure, isoform composition, and distribution of 14-3-3 proteins in different tissues. Different elements of 14-3-3 structure important for dimer formation and recognition of protein targets are analyzed in detail. Special attention is paid to analysis of posttranslational modifications playing important roles in regulation of 14-3-3 function. The data of the literature concerning participation of 14-3-3 in regulation of intercellular contacts and different elements of cytoskeleton formed by microfilaments are analyzed. We also describe participation of 14-3-3 in regulation of small G-proteins and protein kinases important for proper functioning of cytoskeleton. The data on the interaction of 14-3-3 with different components of microtubules are presented, and the probable role of 14-3-3 in developing of certain neurodegenerative diseases is discussed. The data of the literature concerning the role of 14-3-3 in formation and normal functioning of intermediate filaments are also reviewed. It is concluded that due to its adapter properties 14-3-3 plays an important role in cytoskeleton regulation. The cytoskeletal proteins that are abundant in the cell might compete with the other protein targets of 14-3-3 and therefore can indirectly regulate many intracellular processes that are dependent on 14-3-3.

Mitochondrial Dysfunction: The Road to Alpha-Synuclein Oligomerization in PD

While the etiology of Parkinson's disease remains largely elusive, there is accumulating evidence suggesting that mitochondrial dysfunction occurs prior to the onset of symptoms in Parkinson's disease. Mitochondria are remarkably primed to play a vital role in neuronal cell survival since they are key regulators of energy metabolism (as ATP producers), of intracellular calcium homeostasis, of NAD(+)/NADH ratio, and of endogenous reactive oxygen species production and programmed cell death. In this paper, we focus on mitochondrial dysfunction-mediated alpha-synuclein aggregation. We highlight some of the findings that provide proof of evidence for a mitochondrial metabolism control in Parkinson's disease, namely, mitochondrial regulation of microtubule-dependent cellular traffic and autophagic lysosomal pathway. The knowledge that microtubule alterations may lead to autophagic deficiency and may compromise the cellular degradation mechanisms that culminate in the progressive accumulation of aberrant protein aggregates shields new insights to the way we address Parkinson's disease. In line with this knowledge, an innovative window for new therapeutic strategies aimed to restore microtubule network may be unlocked.

Synphilin-1 enhances α-synuclein aggregation in yeast and contributes to cellular stress and cell death in a Sir2-dependent manner

Background

Parkinson's disease is characterized by the presence of cytoplasmic inclusions, known as Lewy bodies, containing both aggregated α-synuclein and its interaction partner, synphilin-1. While synphilin-1 is known to accelerate inclusion formation by α-synuclein in mammalian cells, its effect on cytotoxicity remains elusive.

Methodology/Principal Findings

We expressed wild-type synphilin-1 or its R621C mutant either alone or in combination with α-synuclein in the yeast Saccharomyces cerevisiae and monitored the intracellular localization and inclusion formation of the proteins as well as the repercussions on growth, oxidative stress and cell death. We found that wild-type and mutant synphilin-1 formed inclusions and accelerated inclusion formation by α-synuclein in yeast cells, the latter being correlated to enhanced phosphorylation of serine-129. Synphilin-1 inclusions co-localized with lipid droplets and endomembranes. Consistently, we found that wild-type and mutant synphilin-1 interacts with detergent-resistant membrane domains, known as lipid rafts. The expression of synphilin-1 did not incite a marked growth defect in exponential cultures, which is likely due to the formation of aggresomes and the retrograde transport of inclusions from the daughter cells back to the mother cells. However, when the cultures approached stationary phase and during subsequent ageing of the yeast cells, both wild-type and mutant synphilin-1 reduced survival and triggered apoptotic and necrotic cell death, albeit to a different extent. Most interestingly, synphilin-1 did not trigger cytotoxicity in ageing cells lacking the sirtuin Sir2. This indicates that the expression of synphilin-1 in wild-type cells causes the deregulation of Sir2-dependent processes, such as the maintenance of the autophagic flux in response to nutrient starvation.

Conclusions/Significance

Our findings demonstrate that wild-type and mutant synphilin-1 are lipid raft interacting proteins that form inclusions and accelerate inclusion formation of α-synuclein when expressed in yeast. Synphilin-1 thereby induces cytotoxicity, an effect most pronounced for the wild-type protein and mediated via Sir2-dependent processes.

α - synuclein and Parkinson's disease: the first roadblock

α-synuclein gene mutations are major underlying genetic defects known in familial juvenile onset Parkinson’s disease (PD), and α-synuclein is a major constituent of Lewy Bodies, the pathological hallmark of PD. The normal cellular function of α-synuclein has been elusive, and its exact etiological mechanism in causing dopaminergic neuronal death in PD is also not clearly understood. Very recent reports now indicate that mutant or simply over-expressed α-synuclein could cause damage by interfering with particular steps of neuronal membrane traffic. α-synuclein selectively blocks endoplamic reticulum-to-Golgi transport, thus causing ER stress. A screen in a yeast revealed that α-synuclein toxicity could be suppressed by over-expression of the small GTPase Ypt1/Rab1, and that over-expression of the latter rescues neuron loss in invertebrate and mammalian models of α-synuclein-induced neurodegeneration. α-synuclein may also serve a chaperone function for the proper folding of synaptic SNAREs that are important for neurotransmitter release. We discuss these recent results and the emerging pathophysiological interaction of α-synuclein with components of neuronal membrane traffic.

α - synuclein and Parkinson's disease: the first roadblock

alpha-synuclein gene mutations are major underlying genetic defects known in familial juvenile onset Parkinson's disease (PD), and alpha-synuclein is a major constituent of Lewy Bodies, the pathological hallmark of PD. The normal cellular function of alpha-synuclein has been elusive, and its exact etiological mechanism in causing dopaminergic neuronal death in PD is also not clearly understood. Very recent reports now indicate that mutant or simply over-expressed alpha- synuclein could cause damage by interfering with particular steps of neuronal membrane traffic. alpha-synuclein selectively blocks endoplamic reticulum-to-Golgi transport, thus causing ER stress. A screen in a yeast revealed that alpha- synuclein toxicity could be suppressed by over-expression of the small GTPase Ypt1/Rab1, and that over-expression of the latter rescues neuron loss in invertebrate and mammalian models of alpha-synuclein-induced neurodegeneration. alpha-synuclein may also serve a chaperone function for the proper folding of synaptic SNAREs that are important for neurotransmitter release. We discuss these recent results and the emerging pathophysiological interaction of alpha-synuclein with components of neuronal membrane traffic.

alpha-Synuclein protects SH-SY5Y cells from dopamine toxicity

Dopaminergic human neuroblastoma SH-SY5Y cells were stably transformed to increase expression of alpha-synuclein, a Parkinson's disease-related protein. Transformed cells were more resistant to oxidative insults, showing a cytoprotective role of alpha-synuclein. The expression of redox chaperonins (DJ-1, HSP70, and 14-3-3) was evaluated by Western blotting. Expression of alpha-synuclein reduced HSP70 levels even in the presence of dopamine, with a twofold increase of DJ-1 in the absence of oxidants. DJ-1 is significantly reduced by dopamine, and even more by dopamine and Cu(II). Increased alpha-synuclein expression did not affect 14-3-3, although dopamine increased its level by 60% in wild-type cells. alpha-Synuclein not only upregulated DJ-1, but also shifted all DJ-1 forms to a single spot at pI=5.7 not observed in wild-type cells. Dopamine gradually restored the distribution of DJ-1 forms to a situation similar to wild-type cells, with the form at pI=6.1 progressively enriched under oxidative conditions.

Chaperone-like activities of alpha-synuclein: alpha-synuclein assists enzyme activities of esterases

Alpha-synuclein, a major constituent of Lewy bodies (LBs), has been implicated to play a critical role in the pathogenesis of Parkinson's disease (PD), although the physiological function of alpha-synuclein has not yet been known. Here we have shown that alpha-synuclein, which has no well-defined secondary or tertiary structure, can protect the enzyme activity of microbial esterases against stress conditions such as heat, pH, and organic solvents. In particular, the flexibility of alpha-synuclein and its C-terminal region seems to be important for complex formation, but the structural integrity of the C-terminal region may not be required for stabilization of enzyme activity. In addition, atomic force microscopy (AFM) and in vivo enzyme assays showed highly specific interactions of esterases with alpha-synuclein. Our results indicate that alpha-synuclein not only protects the enzyme activity of microbial esterases in vitro, but also can stabilize the active conformation of microbial esterases in vivo.

Protein phosphatase inhibitor-1 (PPI-1) has protective activities in stress conditions in E. coli

Protein phosphatase inhibitor-1 (PPI-1) is a major inhibitor of protein phosphatase 1 (PP1), which regulates signal transduction in many eukaryotic cellular processes. Biophysical studies have shown that PPI-1 has a large Stokes radius and is heat stable, suggesting that it lacks extensive secondary structures. The unfolded structure of PPI-1 may enable it to interact with many proteins or ligands during stress conditions. Here we show that PPI-1 can act as a protective molecule, inhibiting protein aggregation and guarding E. coli cells against various stresses. Therefore, PPI-1 seems to have a physiological function as a protective molecule as well as regulator of protein serine/threonine phosphatases.