Cyclic-NDGA Effectively Inhibits Human γ-Synuclein Fibrillation, Forms Nontoxic Off-Pathway Species, and Disintegrates Preformed Mature Fibrils.

Parkinson's disease arises from protein misfolding, aggregation, and fibrillation and is characterized by LB (Lewy body) deposits, which contain the protein α-synuclein (α-syn) as their major component. Another synuclein, γ-synuclein (γ-syn), coexists with α-syn in Lewy bodies and is also implicated in various types of cancers, especially breast cancer. It is known to seed α-syn fibrillation after its oxidation at methionine residue, thereby contributing in synucleinopathy. Despite its involvement in synucleinopathy, the search for small molecule inhibitors and modulators of γ-syn fibrillation remains largely unexplored. This work reveals the modulatory properties of cyclic-nordihydroguaiaretic acid (cNDGA), a natural polyphenol, on the structural and aggregational properties of human γ-syn employing various biophysical and structural tools, namely, thioflavin T (ThT) fluorescence, Rayleigh light scattering, 8-anilinonaphthalene-1-sulfonic acid binding, far-UV circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR) spectroscopy, atomic force microscopy, ITC, molecular docking, and MTT-toxicity assay. cNDGA was observed to modulate the fibrillation of γ-syn to form off-pathway amorphous species that are nontoxic in nature at as low as 75 µM concentration. The modulation is dependent on oxidizing conditions, with cNDGA weakly interacting (Kd ∼10-5 M) with the residues at the N-terminal of γ-syn protein as investigated by isothermal titration calorimetry and molecular docking, respectively. Increasing cNDGA concentration results in an increased recovery of monomeric γ-syn as shown by sodium dodecyl sulfate and native-polyacrylamide gel electrophoresis. The retention of native structural properties of γ-syn in the presence of cNDGA was further confirmed by far-UV CD and FTIR. In addition, cNDGA is most effective in suppression of fibrillation when added at the beginning of the fibrillation kinetics and is also capable of disintegrating the preformed mature fibrils. These findings could, therefore, pave the ways for further exploring cNDGA as a potential therapeutic against γ-synucleinopathies.

Modulation of the conformation, fibrillation, and fibril morphologies of human brain α-, ß-, and γ-synuclein proteins by the disaccharide chemical chaperone trehalose.

Human α-, ß-, and γ-synuclein (syn) are natively unfolded proteins present in the brain. Deposition of aggregated α-syn in Lewy bodies is associated with Parkinson's disease (PD) and γ-syn is known to be involved in both neurodegeneration and breast cancer. At physiological pH, while α-syn has the highest propensity for fibrillation followed by γ-syn, ß-syn does not form any fibrils. Fibril formation in these proteins could be modulated by protein structure stabilizing osmolytes such as trehalose which has an exceptional stabilizing effect for globular proteins. We present a comprehensive study of the effect of trehalose on the conformation, aggregation, and fibril morphology of α-, ß-, and γ-syn proteins. Rather than stabilizing the intrinsically disordered state of the synucleins, trehalose accelerates the rate of fibril formation by forming aggregation-competent partially folded intermediate structures. Fibril morphologies are also strongly dependent on the concentration of trehalose with ≤ 0.4M favoring the formation of mature fibrils in α-, and γ-syn with no effect on the fibrillation of ß-syn. At ≥ 0.8M, trehalose promotes the formation of smaller aggregates that are more cytotoxic. Live cell imaging of preformed aggregates of a labeled A90C α-syn shows their rapid internalization into neural cells which could be useful in reducing the load of aggregated species of α-syn. The findings throw light on the differential effect of trehalose on the conformation and aggregation of disordered synuclein proteins with respect to globular proteins and could help in understanding the effect of osmolytes on intrinsically disordered proteins under cellular stress conditions.

Excess membrane binding of monomeric alpha-, beta- and gamma-synuclein is invariably associated with inclusion formation and toxicity.

α-Synuclein (αS) has been well-documented to play a role in human synucleinopathies such as Parkinson's disease (PD) and dementia with Lewy bodies (DLB). First, the lesions found in PD/DLB brains-Lewy bodies and Lewy neurites-are rich in aggregated αS. Second, genetic evidence links missense mutations and increased αS expression to familial forms of PD/DLB. Third, toxicity and cellular stress can be caused by αS under certain experimental conditions. In contrast, the homologs ß-synuclein (ßS) and γ-synuclein (γS) are not typically found in Lewy bodies/neurites, have not been clearly linked to brain diseases and have been largely non-toxic in experimental settings. In αS, the so-called non-amyloid-ß component of plaques (NAC) domain, constituting amino acids 61-95, has been identified to be critical for aggregation in vitro. This domain is partially absent in ßS and only incompletely conserved in γS, which could explain why both homologs do not cause disease. However, αS in vitro aggregation and cellular toxicity have not been firmly linked experimentally, and it has been proposed that excess αS membrane binding is sufficient to induce neurotoxicity. Indeed, recent characterizations of Lewy bodies have highlighted the accumulation of lipids and membranous organelles, raising the possibility that ßS and γS could also become neurotoxic if they were more prone to membrane/lipid binding. Here, we increased ßS and γS membrane affinity by strategic point mutations and demonstrate that these proteins behave like membrane-associated monomers, are cytotoxic and form round cytoplasmic inclusions that can be prevented by inhibiting stearoyl-CoA desaturase.

Computational Study on the Role of γ-Synuclein in Inhibiting the α-Synuclein Aggregation.

BACKGROUND: α-Synuclein (αS) is the precursor protein present in Lewy Bodies that helps in the formation of highly ordered amyloid fibrils that is associated with the occurrence of Parkinson's disease, a neuro-degenerative disorder. Many reports have now been focused on finding the probable targets to weaken this debilitating disease. Recently γ-synuclein (γS), a presynaptic protein, was highlighted to inhibit the aggregation propensity of αS both in vivo and in vitro. However the nature, location and specificity of molecular interactions existing between the αS and γS is not known in spite of the potential importance of γS as an inhibitor of αS. OBJECTIVE: To understand the inhibition of αS aggregation by γS at the molecular level. METHODS: Umbrella sampling method was used along with molecular dynamics simulation to investigate the conformational dynamics, degree of association and molecular interaction between the monomeric units in the αS/γS hetero-dimer. RESULTS AND DISCUSSION: The dissociation energy barrier for αS/γS hetero-dimer was found to be higher than αS/αS homo-dimer. αS can therefore readily form a hetero-dimer by combining with γS than forming a homo-dimer. We also observed strong transient interactions involving hydrogen bonds, salt-bridges and non-bonded contacts between the monomeric units in αS/γS hetero-dimer. CONCLUSION: Our findings suggest that γS may inhibit the aggregation propensity of αS.

Effect of polyols on the structure and aggregation of recombinant human γ-Synuclein, an intrinsically disordered protein.

Polyol osmolytes accumulated in cells under stress are known to promote stability in globular proteins with respect to their increasing hydroxyl groups but their effect on the structure, stability and aggregation of intrinsically disordered proteins (IDPs) is still elusive. The lack of a natively folded structure in intrinsically disordered proteins under physiological conditions results in their aggregation and fibrillation that gives rise to a number of diseases. We have investigated the effect of a series of polyols, ethylene glycol (EG), glycerol, erythritol, xylitol and sorbitol on the fibrillation pathway of recombinant human γ-Synuclein, used as a model, for an IDP known to form fibrils that play a role in neurodegeneration and cancer. With an increase in the number of -OH groups in polyols except EG, we observe a decrease in lag time for fibrillation at equimolar concentrations, suggesting stronger preferential exclusion of polyols that promotes γ-Syn self-association and oligomerization. The polyols act early during nucleation and their diverse effect on the rate of fibrillation suggests the role of favourable solvent-side chain interactions. With increasing -OH group, polyols stabilize the natively unfolded conformation of γ-Syn under non-fibrillating conditions and delay the structural transition to characteristic ß-sheet structure by forming an α-helical intermediate during fibrillation. The results, overall suggest that the effect of osmolytes on IDPs is much more complex than their effect on globular protein stability and aggregation and a fine balance between the dominant unfavourable osmolyte-peptide backbone and favourable osmolyte-charged side chain interactions would govern their stability and aggregation properties.

Effects of phosphatidylcholine membrane fluidity on the conformation and aggregation of N-terminally acetylated α-synuclein.

Membrane association of α-synuclein (α-syn), a neuronal protein associated with Parkinson's disease (PD), is involved in α-syn function and pathology. Most previous studies on α-syn-membrane interactions have not used the physiologically relevant N-terminally acetylated (N-acetyl) α-syn form nor the most naturally abundant cellular lipid, i.e. phosphatidylcholine (PC). Here, we report on how PC membrane fluidity affects the conformation and aggregation propensity of N-acetyl α-syn. It is well established that upon membrane binding, α-syn adopts an α-helical structure. Using CD spectroscopy, we show that N-acetyl α-syn transitions from α-helical to disordered at the lipid melting temperature (Tm ). We found that this fluidity sensing is a robust characteristic, unaffected by acyl chain length (Tm = 34-55 °C) and preserved in its homologs ß- and γ-syn. Interestingly, both N-acetyl α-syn membrane binding and amyloid formation trended with lipid order (1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) > 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/sphingomyelin/cholesterol (2:2:1) ≥ DOPC), with gel-phase vesicles shortening aggregation kinetics and promoting fibril formation compared to fluid membranes. Furthermore, we found that acetylation enhances binding to PC micelles and small unilamellar vesicles with high curvature (r ∼16-20 nm) and that DPPC binding is reduced in the presence of cholesterol. These results confirmed that the exposure of hydrocarbon chains (i.e. packing defects) is essential for binding to zwitterionic gel membranes. Collectively, our in vitro results suggest that N-acetyl α-syn localizes to highly curved, ordered membranes inside a cell. We propose that age-related changes in membrane fluidity can promote the formation of amyloid fibrils, insoluble materials associated with PD.

Comparative Analysis of the Conformation, Aggregation, Interaction, and Fibril Morphologies of Human α-, ß-, and γ-Synuclein Proteins.

The human synuclein (syn) family is comprised of α-, ß-, and γ-syn proteins. α-syn has the highest propensity for aggregation, and its aggregated forms accumulate in Lewy bodies (LB) and Lewy neurites, which are involved in Parkinson's disease (PD). ß- and γ-syn are absent in LB, and their exact role is still enigmatic. ß-syn does not form aggregates under physiological conditions (pH 7.4), while γ-syn is associated with neural and non-neural diseases like breast cancer. Because of their similar regional distribution in the brain, natively unfolded structure, and high degree of sequence homology, studying the effect of the environment on their conformation, interactions, fibrillation, and fibril morphologies has become important. Our studies show that high temperatures, low pH values, and high concentrations increase the rate of fibrillation of α- and γ-syn, while ß-syn forms fibrils only at low pH. Fibril morphologies are strongly dependent on the immediate environment of the proteins. The high molar ratio of ß-syn inhibits the fibrillation in α- and γ-syn. However, preformed seed fibrils of ß- and γ-syn do not affect fibrillation of α-syn. Surface plasmon resonance data show that interactions between α- and ß-syn, ß- and γ-syn, and α- and γ-syn are weak to moderate in nature and can be physiologically significant in counteracting several adverse conditions in the cells that trigger their aggregation. These studies could be helpful in understanding collective human synuclein behavior in various protein environments and in the modulation of the homeostasis between ß-syn and healthy versus corrupt α- and γ-syn that can potentially affect PD pathology.

Structural insights into tumor-specific chaperoning activity of gamma synuclein in protecting estrogen receptor alpha 36 and its role in tamoxifen resistance in breast cancer.

Gamma synuclein (γSyn), a tumor-specific molecular chaperone, protects Hsp90 client proteins like ERα36 and stimulates rapid membrane-initiated estrogen signalling in breast cancer cells. However, the structural perspectives of this tumor-specific chaperone function of γSyn remains unclear. Hence, in this present work, we studied the conformational dynamics of ERα36 in the absence and presence of Hsp90 and γSyn. Results indicate that in a chaperone-free state, ERα36 undergoes an inter-domain movement and exposes the hydrophobic patch of residues that are responsible for binding with ubiquitin. However, independent of Hsp90, γSyn, by establishing transient interactions, prevents interdomain movement, unveils the co-activator binding groove, masks the ubiquitin-binding residues and maintains 'open' pocket conformation of LBD. By doing so, γSyn effectively protects ERα36 from degradation and maintains its functional state like Hsp90 based chaperoning machinery but independent of ATP. Our studies also show that the γSyn protected conformation of ERα36 can effectively bind with both estradiol (E2) and 4-hydroxy tamoxifen (4-OHT). Although they exhibit unique binding modes, they maintained the functionally active conformation of ERα36. Interestingly, the molecular dynamics simulation studies showed that 4-OHT, like γSyn, prevented the interdomain movements, primes the co-activator binding groove of ERα36 for complexation with downstream signalling proteins and this mechanism explains its agonist activity and associated anti-estrogen resistance observed in the presence of ERα36. The observed differences in the chaperoning mechanism of γSyn sheds light on its selectivity over Hsp90 in cancer cells, for promoting rapid protection of crucial oncogenic proteins. Based on our findings, we speculate that the compounds, which can hamper association of γSyn with ERα36 and/or can arrest ERα36 in an ubiquitin binding state, would be promising alternatives for treating ERα36 expressed breast carcinomas.

Dimerization propensities of Synucleins are not predictive for Synuclein aggregation.

Aggregation and fibril formation of human alpha-Synuclein (αS) are neuropathological hallmarks of Parkinson's disease and other synucleinopathies. The molecular mechanisms of αS aggregation and fibrillogenesis are largely unknown. Several studies suggested a sequence of events from αS dimerization via oligomerization and pre-fibrillar aggregation to αS fibril formation. In contrast to αS, little evidence suggests that γS can form protein aggregates in the brain, and for ßS its neurotoxic properties and aggregation propensities are controversially discussed. These apparent differences in aggregation behavior prompted us to investigate the first step in Synuclein aggregation, i.e. the formation of dimers or oligomers, by Bimolecular Fluorescence Complementation in cells. This assay showed some Synuclein-specific limitations, questioning its performance on a single cell level. Nevertheless, we unequivocally demonstrate that all Synucleins can interact with each other in a very similar way. Given the divergent aggregation properties of the three Synucleins this suggests that formation of dimers is not predictive for the aggregation of αS, ßS or γS in the aged or diseased brain.

Synuclein γ protects Akt and mTOR and renders tumor resistance to Hsp90 disruption.

Heat shock protein (Hsp)90 regulates many key pathways in oncogenesis, including Akt and mammalian target of rapamycin (mTOR). The strengths of disruption of Hsp90 in cancer therapy include their versatility in inhibiting a wide range of oncogenic pathways. The present study demonstrated that synuclein γ (SNCG) protects the functions of Akt and mTOR in the condition when the function of Hsp90 is blocked. Disruption of Hsp90 abolished Akt activity and mTOR signaling. However, expression of SNCG restored Akt activity and mTOR signaling. SNCG bound to Akt and mTOR in the presence and absence of Hsp90. Specifically, the C-terminal (Gln106-Asp127) of SNCG bound to the loop connecting αC helix and ß4 sheet of the kinase domain of Akt. SNCG renders resistance to 17-AAG-induced apoptosis both in vitro and in tumor xenograft. A clinical follow-up study indicates that patients with an SNCG-positive breast cancer have a significantly shorter disease-free survival and overall survival than patients with SNCG-negative tumors. The present study indicates that SNCG protects Hsp90 client proteins of Akt and mTOR, and renders drug resistance to Hsp90 disruption.

Investigation of intramolecular dynamics and conformations of α-, ß- and γ-synuclein.

The synucleins are a family of natively unstructured proteins consisting of α-, ß-, and γ-synuclein which are primarily expressed in neurons. They have been linked to a wide variety of pathologies, including neurological disorders, such as Parkinson's disease (α-synuclein) and dementia with Lewy bodies (α- and ß-synuclein), as well as various types of cancers (γ-synuclein). Self-association is a key pathological feature of many of these disorders, with α-synuclein having the highest propensity to form aggregates, while ß-synuclein is the least prone. Here, we used a combination of fluorescence correlation spectroscopy and single molecule Förster resonance energy transfer to compare the intrinsic dynamics of different regions of all three synuclein proteins to investigate any correlation with putative functional or dysfunctional interactions. Despite a relatively high degree of sequence homology, we find that individual regions sample a broad range of diffusion coefficients, differing by almost a factor of four. At low pH, a condition that accelerates aggregation of α-synuclein, on average smaller diffusion coefficients are measured, supporting a hypothesis that slower intrachain dynamics may be correlated with self-association. Moreover, there is a surprising inverse correlation between dynamics and bulkiness of the segments. Aside from this observation, we could not discern any clear relationship between the physico-chemical properties of the constructs and their intrinsic dynamics. This work suggests that while protein dynamics may play a role in modulating self-association or interactions with other binding partners, other factors, particularly the local cellular environment, may be more important.

Defining the oligomerization state of γ-synuclein in solution and in cells.

γ-Synuclein is expressed at high levels in neuronal cells and in multiple invasive cancers. Like its family member α-synuclein, γ-synuclein is thought to be natively unfolded but does not readily form fibrils. The function of γ-synuclein is unknown, but we have found that it interacts strongly with the enzyme phospholipase Cß (PLCß), altering its interaction with G proteins. As a first step in determining its role, we have characterized its oligomerization using fluorescence homotransfer, photon-counting histogram analysis, and native gel electrophoresis. We found that when its expressed in Escherichia coli and purified, γ-synuclein appears monomeric on chromatographs under denaturing conditions, but under native conditions, it appears as oligomers of varying sizes. We followed the monomer-to-tetramer association by labeling the protein with fluorescein and following the concentration-dependent loss in fluorescence anisotropy resulting from fluorescence homotransfer. We also performed photon-counting histogram analysis at increasing concentrations of fluorescein-labeled γ-synuclein and found concentration-dependent oligomerization. Addition of PLCß2, a strong γ-synuclein binding partner whose cellular expression is correlated with γ-synuclein, results in disruption of γ-synuclein oligomers. Similarly, its binding to lipid membranes promotes the monomer form. When we exogenously express γ-synuclein or microinject purified protein into cells, the protein appears monomeric. Our studies show that even though purified γ-synuclein form oligomers, when binding partners are present, as in cells, it dissociates to a monomer to bind these partners, which in turn may modify protein function and integrity.

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.

Molecular dynamic simulations of the tubulin-human gamma synuclein complex: structural insight into the regulatory mechanism involved in inducing resistance against Taxol.

Members of the synuclein family (α, ß and γ synucleins) are intrinsically disordered in nature and play a crucial role in the progression of various neurodegenerative disorders and cancers. The association of γSyn with both BubR1 as well as microtubule subunits renders resistance against various anti-cancer drugs. However, the structural aspects underlying drug resistance have not been explored. In this study, the mechanism involved in the association between γSyn and microtubule subunits (αßTub) was investigated and the results reveal a strong interaction between γSyn and the tail regions of αßTub. Complexation of γSyn induces conformational rearrangements in the nucleotide binding loops (NBL), interdomain and tail regions of both α and ßTub. Moreover, in ßTub, the massive displacement observed in M and S loops significantly alters the binding site of microtubule targeting drugs like Taxol. The resulting weak association between Taxol and ßTub of the γSyn-αßTub complex was confirmed by molecular dynamic simulation studies. In addition, the effect of Taxol on NBL, M and S loops of αßTub, is reversed in the presence of γSyn. These results clearly indicate that the presence of γSyn annulled the allosteric regulation imposed by Taxol on the αßTub complex as well as preventing the binding of microtubule targeting drugs, which eventually leads to the development of resistance against these drugs in cancer cells.

Monomeric synucleins generate membrane curvature.

Synucleins are a family of presynaptic membrane binding proteins. α-Synuclein, the principal member of this family, is mutated in familial Parkinson disease. To gain insight into the molecular functions of synucleins, we performed an unbiased proteomic screen and identified synaptic protein changes in αßγ-synuclein knock-out brains. We observed increases in the levels of select membrane curvature sensing/generating proteins. One of the most prominent changes was for the N-BAR protein endophilin A1. Here we demonstrate that the levels of synucleins and endophilin A1 are reciprocally regulated and that they are functionally related. We show that all synucleins can robustly generate membrane curvature similar to endophilins. However, only monomeric but not tetrameric α-synuclein can bend membranes. Further, A30P α-synuclein, a Parkinson disease mutant that disrupts protein folding, is also deficient in this activity. This suggests that synucleins generate membrane curvature through the asymmetric insertion of their N-terminal amphipathic helix. Based on our findings, we propose to include synucleins in the class of amphipathic helix-containing proteins that sense and generate membrane curvature. These results advance our understanding of the physiological function of synucleins.

Contrasting effects of α-synuclein and γ-synuclein on the phenotype of cysteine string protein α (CSPα) null mutant mice suggest distinct function of these proteins in neuronal synapses.

In neuronal synapses, neurotransmitter-loaded vesicles fuse with presynaptic plasma membrane in a complex sequence of tightly regulated events. The assembly of specialized SNARE complexes plays a pivotal role in this process. The function of the chaperone cysteine string protein α (CSPα) is important for synaptic SNARE complex formation, and mice lacking this protein develop severe synaptic dysfunction and neurodegeneration that lead to their death within 3 months after birth. Another presynaptic protein, α-synuclein, also potentiates SNARE complex formation, and its overexpression rescues the phenotype of CSPα null mutant mice, although these two proteins use different mechanisms to achieve this effect. α-Synuclein is a member of a family of three related proteins whose structural similarity suggests functional redundancy. Here, we assessed whether γ-synuclein shares the ability of α-synuclein to bind synaptic vesicles and ameliorate neurodegeneration caused by CSPα deficiency in vivo. Although the N-terminal lipid-binding domains of the two synucleins showed similar affinity for purified synaptic vesicles, the C-terminal domain of γ-synuclein was not able to interact with synaptobrevin-2/VAMP2. Consequently, overexpression of γ-synuclein did not have any noticeable effect on the phenotype of CSPα null mutant mice. Our data suggest that the functions of α- and γ-synucleins in presynaptic terminals are not fully redundant.

Quantifying interactions of ß-synuclein and γ-synuclein with model membranes.

The synucleins are a family of proteins involved in numerous neurodegenerative pathologies [α-synuclein and ß-synuclein (ßS)], as well as in various types of cancers [γ-synuclein (γS)]. While the connection between α-synuclein and Parkinson's disease is well established, recent evidence links point mutants of ßS to dementia with Lewy bodies. Overexpression of γS has been associated with enhanced metastasis and cancer drug resistance. Despite their prevalence in such a variety of diseases, the native functions of the synucleins remain unclear. They have a lipid-binding motif in their N-terminal region, which suggests interactions with biological membranes in vivo. In this study, we used fluorescence correlation spectroscopy to monitor the binding properties of ßS and γS to model membranes and to determine the free energy of the interactions. Our results show that the interactions are most strongly affected by the presence of both anionic lipids and bilayer curvature, while membrane fluidity plays a very minor role. Quantifying the lipid-binding properties of ßS and γS provides additional insights into the underlying factors governing the protein-membrane interactions. Such insights not only are relevant to the native functions of these proteins but also highlight their contributions to pathological conditions that are either mediated or characterized by perturbations of these interactions.

Insight into residues involved in the structure and function of the breast cancer associated protein human gamma synuclein.

Aberrantly expressed human gamma synuclein (SNCG) interacts with BubR1 and heat shock protein 70 (Hsp70) in late stages of breast and ovarian cancer. This interaction is essential for progression, development and survival of cancer cells. A short, synthetically designed ankyrin-repeat-containing peptide (ANK peptide) was proven to inhibit the activity of SNCG. However, the potential binding site residues of SNCG responsible for its oncogenic function have not been reported so far. The objectives of this study were to generate a three-dimensional model of SNCG and to identify the key residues involved in interaction with BubR1, ANK peptide and Hsp70. Our study is the first attempt to report the specific binding of SNCG with the TPR motif of BubR1 and the 18kDa region of Hsp70. Our findings provide novel insights into the mechanism of interaction of SNCG, and can act as a basis for the ongoing drug design and discovery process aimed at treating breast and ovarian cancer.

The synucleins are a family of redox-active copper binding proteins.

Thermodynamic studies in conjunction with EPR confirm that α-synuclein, ß-synuclein, and γ-synuclein bind copper(II) in a high affinity 1:1 stoichiometry. γ-Synuclein demonstrates the highest affinity, in the picomolar range, while α-synuclein and ß-synuclein both bind copper(II) with nanomolar affinity. The copper center on all three proteins demonstrates reversible or partly reversible redox cycling. Various mutations show that the primary coordinating ligand for copper(II) is located within the N-terminal regions between residues 2-9. There is also a contribution from the C-terminus in conjunction with the histidine at position 50 in α-synuclein and position 65 in ß-synuclein, although these regions appear to have little effect on overall coordination stability. These histidines and the C-terminus, however, appear to be critical to the redox engine of the proteins.

Porcine gamma-synuclein: molecular cloning, expression analysis, chromosomal localization and functional expression.

The gamma-synuclein protein is involved in breast carcinogenesis and has also been implicated in other forms of cancer and in ocular diseases. Furthermore, gamma-synuclein is believed to have a role in certain neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. This work reports the cloning and characterization of the porcine (Sus scrofa) gamma-synuclein cDNA (SNCG). The SNCG cDNA was amplified by reverse transcriptase polymerase chain reaction (RT-PCR) using oligonucleotide primers derived from in silico sequences. The porcine SNCG cDNA codes for a protein of 126 amino acids which shows a high similarity to bovine (90%), human (87%) and mouse (83%) gamma-synuclein. A genomic clone containing the entire porcine SNCG gene was isolated and its genomic organization determined. The gene is composed of five exons, the general structure being observed to be very similar to that of the human SNCG gene. Expression analysis by quantitative real-time RT-PCR revealed the presence of SNCG transcripts in all examined organs and tissues. Differential expression was observed, with very high levels of SNCG mRNA in fat tissue and high expression levels in spleen, cerebellum, frontal cortex and pituitary gland. Expression analysis also showed that porcine SNCG transcripts could be detected in different brain regions during early stages of embryo development. The porcine SNCG orthologue was mapped to chromosome 14q25-q29. The distribution of recombinant porcine gamma-synuclein was studied in three different transfected cell lines and the protein was found to be predominantly localized in the cytoplasm.