One single method to produce native and Tat-fused recombinant human α-synuclein in Escherichia coli

α-Synuclein is required for sperm exocytosis at a post-fusion stage

The sperm acrosome is a large dense-core granule whose contents are secreted by regulated exocytosis at fertilization through the opening of numerous fusion pores between the acrosomal and plasma membranes. In other cells, the nascent pore generated when the membrane surrounding a secretory vesicle fuses with the plasma membrane may have different fates. In sperm, pore dilation leads to the vesiculation and release of these membranes, together with the granule contents. α-Synuclein is a small cytosolic protein claimed to exhibit different roles in exocytic pathways in neurons and neuroendocrine cells. Here, we scrutinized its function in human sperm. Western blot revealed the presence of α-synuclein and indirect immunofluorescence its localization to the acrosomal domain of human sperm. Despite its small size, the protein was retained following permeabilization of the plasma membrane with streptolysin O. α-Synuclein was required for acrosomal release, as demonstrated by the inability of an inducer to elicit exocytosis when permeabilized human sperm were loaded with inhibitory antibodies to human α-synuclein. The antibodies halted calcium-induced secretion when introduced after the acrosome docked to the cell membrane. Two functional assays, fluorescence and transmission electron microscopies revealed that the stabilization of open fusion pores was responsible for the secretion blockage. Interestingly, synaptobrevin was insensitive to neurotoxin cleavage at this point, an indication of its engagement in cis SNARE complexes. The very existence of such complexes during AE reflects a new paradigm. Recombinant α-synuclein rescued the inhibitory effects of the anti-α-synuclein antibodies and of a chimeric Rab3A-22A protein that also inhibits AE after fusion pore opening. We applied restrained molecular dynamics simulations to compare the energy cost of expanding a nascent fusion pore between two model membranes and found it higher in the absence than in the presence of α-synuclein. Hence, our results suggest that α-synuclein is essential for expanding fusion pores.

Cholesterol-containing lipid nanodiscs promote an α-synuclein binding mode that accelerates oligomerization

Dysregulation of the biosynthesis of cholesterol and other lipids has been implicated in many neurological diseases, including Parkinson's disease. Misfolding of α-synuclein (α-Syn), the main actor in Parkinson's disease, is associated with changes in a lipid environment. However, the exact molecular mechanisms underlying cholesterol effect on α-Syn binding to lipids as well as α-Syn oligomerization and fibrillation remain elusive, as does the relative importance of cholesterol compared to other factors. We probed the interactions and fibrillation behaviour of α-Syn using styrene-maleic acid nanodiscs, containing zwitterionic and anionic lipid model systems with and without cholesterol. Surface plasmon resonance and thioflavin T fluorescence assays were employed to monitor α-Syn binding, as well as fibrillation in the absence and presence of membrane models. 1 H-15 N-correlated NMR was used to monitor the fold of α-Syn in response to nanodisc binding, determining individual residue apparent affinities for the nanodisc-contained bilayers. The addition of cholesterol inhibited α-Syn interaction with lipid bilayers and, however, significantly promoted α-Syn fibrillation, with a more than a 20-fold reduction of lag times before fibrillation onset. When α-Syn bilayer interactions were analysed at an individual residue level by solution-state NMR, we observed two different effects of cholesterol. In nanodiscs made of DOPC, the addition of cholesterol modulated the NAC part of α-Syn, leading to stronger interaction of this region with the lipid bilayer. In contrast, in the nanodiscs comprising DOPC, DOPE and DOPG, the NAC part was mostly unaffected by the presence of cholesterol, while the binding of the N and the C termini was both inhibited.

Peripheral inflammation exacerbates α-synuclein toxicity and neuropathology in Parkinson's models

AIMS

Parkinson's disease and related disorders are devastating neurodegenerative pathologies. Since α-synuclein was identified as a main component of Lewy bodies and neurites, efforts have been made to clarify the pathogenic mechanisms of α-synuclein's detrimental effects. α-synuclein oligomers are the most harmful species and may recruit and activate glial cells. Inflammation is emerging as a bridge between genetic susceptibility and environmental factors co-fostering Parkinson's disease. However, direct evidence linking inflammation to the harmful activities of α-synuclein oligomers or to the Parkinson's disease behavioural phenotype is lacking.

METHODS

To clarify whether neuroinflammation influences Parkinson's disease pathogenesis, we developed: (i) a 'double-hit' approach in C57BL/6 naive mice where peripherally administered lipopolysaccharides were followed by intracerebroventricular injection of an inactive oligomer dose; (ii) a transgenic 'double-hit' model where lipopolysaccharides were given to A53T α-synuclein transgenic Parkinson's disease mice.

RESULTS

Lipopolysaccharides induced a long-lasting neuroinflammatory response which facilitated the detrimental cognitive activities of oligomers. LPS-activated microglia and astrocytes responded differently to the oligomers with microglia activating further and acquiring a pro-inflammatory M1 phenotype, while astrocytes atrophied. In the transgenic 'double-hit' A53T mouse model, lipopolysaccharides aggravated cognitive deficits and increased microgliosis. Again, astrocytes responded differently to the double challenge. These findings indicate that peripherally induced neuroinflammation potentiates the α-synuclein oligomer's actions and aggravates cognitive deficits in A53T mice.

CONCLUSIONS

The fine management of both peripheral and central inflammation may offer a promising therapeutic approach to prevent or slow down some behavioural aspects in α-synucleinopathies.

A method of purifying alpha-synuclein in E. coli without chromatography

Research has implicated alpha-synuclein (aSyn) in pathological protein aggregation observed in almost all patients with Parkinson's disease and more than 50% of patients with Alzheimer's disease. An easy and inexpensive method of purifying aSyn and developing an in vitro model system of Lewy body formation would enhance basic biomedical research. We report aSyn purification technique that leverages the amyloidogenic property of aSyn suitable for purifying monomeric aSyn without chromatography and denaturing agents. We expressed full-length and untagged aSyn in Rosetta(DE3) pLysS and purified ~60 μg of aSyn from 500 mL culture within 24 h. After IPTG-induced expression of aSyn in E. coli, we disrupted the cells with a sonicator. We centrifuged the cell lysate in a 15 mL tube, which leads to aSyn-induced aggregation of native E. coli proteins. After removing aggregates, centrifugation in a 30 kDa cut-off filter followed by a 10 kDa cut-off filter led to purified water-soluble aSyn. The identity of aSyn was confirmed by Western blot using anti-aSyn antibody and Edman sequencing. Its mass was determined to be 14.6 kDa using a MALDI TOF-MS mass spectrometer. The majority of aSyn led to water-suspended (as opposed to precipitated) aggregation of E. coli proteins with visible fibrous structures. The broad-spectrum binding and amyloidogenic property of aSyn is thus not only useful for inexpensive aSyn production for diverse applications, but it also expands studying its possible roles in human physiology. The aggregate of E. coli proteins induced by aSyn during the purification process may serve as a Lewy body model.

Expression and purification of amyloid β-protein, tau, and α-synuclein in Escherichia coli: a review

Misfolding and accumulation of amyloidogenic proteins into various forms of aggregated intermediates and insoluble amyloid fibrils is associated with more than 50 human diseases. Large amounts of high-quality amyloid proteins are required for better probing of their aggregation and neurotoxicity. Due to their intrinsic hydrophobicity, it is a challenge to obtain amyloid proteins with high yield and purity, and they have attracted the attention of researchers from all over the world. The rapid development of bioengineering technology provides technical support for obtaining large amounts of recombinant amyloidogenic proteins. This review discusses the available expression and purification methods for three amyloid proteins including amyloid β-protein, tau, and α-synuclein in microbial expression systems, especially Escherichia coli, and discusses the advantages and disadvantages of these methods. Importantly, these protocols can also be referred to for the expression and purification of other hydrophobic proteins.

An efficient method for recombinant production of human alpha synuclein in Escherichia coli using thioredoxin as a fusion partner

Herein, we describe a simple and efficient approach to produce recombinant human α-synuclein (hAS) with high purity from Escherichia coli (E. coli). The cDNA for hAS was inserted into plasmid pET32a and expressed in E. coli BL21 (DE3) with an N-terminal tag containing E. coli thioredoxin (trx), followed by a histidine hexapeptide, and a tobacco etch virus (TEV) protease cleavage site (trx-6His-TEV). The fusion protein, trx-hAS, was initially released by osmotic shock treatment from the host cells and subsequently purified using a nickel affinity chromatography. A TEV protease cleavage step was performed to liberate the target protein, hAS, from the fusion partner, trx. Finally, an additional nickel affinity chromatography was performed to further purify the digested product. The yield of this method is ∼25 mg of tag-less protein (with ∼99% purity) per liter of culture volume. Reverse phase HPLC (RP-HPLC) and electrospray ionization (ESI) mass spectrometry confirmed the purity and authenticity of the purified protein. Thioflavin T (ThT) fluorescence assay, transmission electron microscopy (TEM), and circular dichroism (CD) spectroscopy demonstrated that the purified proteins form fibrils. Our protocol not only provides a convenient procedure for preparing highly pure hAS, but also requires very little specialized laboratory techniques.

Alpha-synuclein oligomers impair memory through glial cell activation and via Toll-like receptor 2

Alpha-synuclein oligomers (α-synOs) are emerging as crucial factors in the pathogenesis of synucleinopathies. Although the connection between neuroinflammation and α-syn still remains elusive, increasing evidence suggests that extracellular moieties activate glial cells leading to neuronal damage. Using an acute mouse model, we explored whether α-synOs induce memory impairment in association to neuroinflammation, addressing Toll-like receptors 2 and 4 (TLR2 and TLR4) involvement. We found that α-synOs abolished mouse memory establishment in association to hippocampal glial activation. On brain slices α-synOs inhibited long-term potentiation. Indomethacin and Ibuprofen prevented the α-synOs-mediated detrimental actions. Furthermore, while the TLR2 functional inhibitor antibody prevented the memory deficit, oligomers induced memory deficits in the TLR4 knockout mice. In conclusion, solely α-synOs induce memory impairment likely inhibiting synaptic plasticity. α-synOs lead to hippocampal gliosis that is involved in memory impairment. Moreover, while the oligomer-mediated detrimental actions are TLR2 dependent, the involvement of TLR4 was ruled out.

Investigation of the effects of carbon-based nanomaterials on A53T alpha-synuclein aggregation using a whole-cell recombinant biosensor

The aggregation of alpha-synuclein (αS), natively unstructured presynaptic protein, is a crucial factor leading to the pathogenesis of Parkinson’s disease (PD) and other related disorders. Recent studies have shown prefibrillar and oligomeric intermediates of αS as toxic to the cells. Herein, split-luciferase complementation assay is used to design a “signal-on” biosensor to monitor oligomerization of A53T αS inside the cells. Then, the effect of carbon-based nanomaterials, such as graphene quantum dots (GQDs) and graphene oxide quantum dots (GOQDs), on A53T αS oligomerization in vitro and in living cells is investigated. In this work, for the first time, it was found that GQDs at a concentration of 0.5 μg/mL can promote A53T αS aggregation by shortening the nucleation process, which is the key rate-determining step of fibrillation, thereby making a signal-on biosensor. While these nanomaterials may cross the blood–brain barrier because of their small sizes, the interaction between αS and GQDs may contribute to PD etiology.

Tat-enhanced delivery of the C terminus of HDAg-L inhibits assembly and secretion of hepatitis D virus

Hepatitis D virus (HDV) contains a single-stranded circular RNA genome that encodes two forms of hepatitis delta antigen (HDAg), the small delta antigen (HDAg-S) and the large delta antigen (HDAg-L). The two proteins have an identical amino acid sequence, except that HDAg-L has a 19-amino-acid extension at the C terminus. The domain spanning amino acid residues 198-210 of the HDAg-L (HDAg-L(198-210)) contains a nuclear export signal (NES), which is important for the nuclear export of HDV ribonucleoprotein to the cytoplasm. In this study, we established a cell permeable TAT-HA-HDAg-L(198-210) fusion protein using an E. coli protein expression system, to determine its function during HDV infection. The cytotoxicity of the TAT-HA-HDAg-L(198-210) fusion protein was investigated using an MTT assay, while a GST pull-down assay revealed that the TAT-HA-HDAg-L(198-210) fusion protein interfered with the interaction between HDAg-L and clathrin heavy chain (CHC). In addition, the cellular distribution of HDAg-L, in the presence of HBsAg, was observed by immunofluorescence staining and the TAT-HA-HDAg-L(198-210) fusion protein was found to impede the nuclear export of HDAg-L. Furthermore, assembly of HDV virus-like particles (VLPs) was decreased by the expression of the TAT-HDAg-L(198-210) fusion protein. The TAT-HA-HDAg-L(198-210) fusion protein also inhibited virus particle assembly and HDV secretion in a mouse model. These results suggest that the TAT-HA-HDAg-L(198-210) fusion protein inhibits the nuclear export of HDAg-L and competes with the C terminus of HDAg-L for interaction with CHC, and may have potential as a therapeutic agent for HDV infection.

TiO2 Nanoparticles as Potential Promoting Agents of Fibrillation of α-Synuclein, a Parkinson's Disease-Related Protein

Background: In recent years, nanomaterials have been widely used in large quantities which make people be more frequently exposed to the chemically synthesized nanoparticles (NPs). When NPs are introduced into an organism, they may interact with a variety of cellular components with yet largely unknown pathological consequences. Objective: It was found that NPs enhance the rate of protein fibrillation in the brain by decreasing the lag time for nucleation. Protein fibrillation is implicated in the pathogenesis of the several neurodegenerative diseases such as Parkinson's disease (PD). α-Synuclein (αS) is natively an unfolded protein which is involved in the pathogenesis of PD. In the present study, we have analyzed the effects of three different NPs on αS fibrillation. Materials and Methods: αS protein expression and purifi cation was done and fibrils formation was induced in the absence or presence of the three types of NPs (i. e., TiO2, SiO2, and SnO2). The enhancement of the fluorescence emission of Thiofl avin T (ThT) and transmission electron microscopy (TEM) were used to monitor the appearance and growth of the fibrils. The adsorption of αS monomers on the surface of NPs was investigated by tyrosine fluorescence emission measurements. Results: We found that TiO2-NPs enhances αS fibril formation even at a concentration of 5 μg.mL^-1, while the two other NPs show no significant effect on the kinetics of the fibrillation. Intrinsic tyrosine emission measurement has confirmed that the TiO2-NPs interact with αS fibrillation products. It is suggested that TiO2- NPs may enhance the nucleation of αS protein that leads to protein fibril formation. Conclusion: The fibrillization process of αS protein is profoundly affected by the presence of TiO2-NPs. This finding unveils the neurotoxicity potential of the TiO2-NPs, which may be considered as a probable risk for PD.

Applications and Challenges for Use of Cell-Penetrating Peptides as Delivery Vectors for Peptide and Protein Cargos

The hydrophilic nature of peptides and proteins renders them impermeable to cell membranes. Thus, in order to successfully deliver peptide and protein-based therapeutics across the plasma membrane or epithelial and endothelial barriers, a permeation enhancing strategy must be employed. Cell-penetrating peptides (CPPs) constitute a promising tool and have shown applications for peptide and protein delivery into cells as well as across various epithelia and the blood-brain barrier (BBB). CPP-mediated delivery of peptides and proteins may be pursued via covalent conjugation of the CPP to the cargo peptide or protein or via physical complexation obtained by simple bulk-mixing of the CPP with its cargo. Both approaches have their pros and cons, and which is the better choice likely relates to the physicochemical properties of the CPP and its cargo as well as the route of administration, the specific barrier and the target cell. Besides the physical barrier, a metabolic barrier must be taken into consideration when applying peptide-based delivery vectors, such as the CPPs, and stability-enhancing strategies are commonly employed to prolong the CPP half-life. The mechanisms by which CPPs translocate cell membranes are believed to involve both endocytosis and direct translocation, but are still widely investigated and discussed. The fact that multiple factors influence the mechanisms responsible for cellular CPP internalization and the lack of sensitive methods for detection of the CPP, and in some cases the cargo, further complicates the design and conduction of conclusive mechanistic studies.

Cell-Penetrating Peptides as Carriers for Oral Delivery of Biopharmaceuticals

Oral delivery of biopharmaceuticals, for example peptides and proteins, constitutes a great challenge in drug delivery due to their low chemical stability and poor permeation across the intestinal mucosa, to a large extent limiting the mode of administration to injections, which is not favouring patient compliance. Nevertheless, cell-penetrating peptides (CPPs) have shown promising potential as carriers to overcome the epithelium, and this minireview highlights recent knowledge gained within the field of CPP-mediated transepithelial delivery of therapeutic peptides and proteins from the intestine. Two approaches may be pursued: co-administration of the carrier and therapeutic peptide in the form of complexes obtained by simple bulk mixing, or administration of covalent conjugates demanding more advanced production methodologies. These formulation approaches have their pros and cons, and which is to be preferred depends on the physicochemical properties of both the specific CPP and the specific cargo. In addition to the physical epithelial barrier, a metabolic barrier must be overcome in order to obtain CPP-mediated delivery of a cargo drug from the intestine, and a number of strategies have been employed to delay enzymatic degradation of the CPP. The mechanisms by which CPPs translocate across membranes are not fully understood, but possibly involve endocytosis as well as direct translocation, and the CPP-mediated transepithelial delivery of cargo drugs thus likely involves similar mechanisms for the initial membrane interaction and translocation. However, the mechanisms responsible for transcytosis of the cargo drug, if taken up by an endocytic mechanism, or direct translocation across the epithelium are so far not known.

Conjugation of cell-penetrating peptides to parathyroid hormone affects its structure, potency, and transepithelial permeation

Delivery of therapeutic peptides and proteins by the use of cell-penetrating peptides (CPPs) as carriers has been suggested as a feasible strategy. The aim of the present study was to investigate the effect of conjugating a series of well-known CPPs to the biologically active part of parathyroid hormone, i.e., PTH(1-34), and to evaluate the effect with regard to secondary structure, potency in Saos-2 cells, immunogenicity, safety, as well as the transepithelial permeation across monolayers by using the Caco-2 cell culture model. Further, co-administration of CPP and PTH(1-34) as an alternative to covalent conjugation was compared with regard to the transepithelial permeation. CPP-conjugated PTH(1-34) fusion peptides were successfully expressed in Escherichia coli and purified from inclusion bodies. No clear correlation between the degree of secondary structure of the CPP-conjugated PTH(1-34) fusion peptides and their potency was found, albeit a general decrease in permeation was observed for both N- and C-terminally CPP-conjugated PTH(1-34) as compared to native PTH(1-34). However, attachment of CPP to the N-terminus significantly increased permeation across Caco-2 cell monolayers as compared to the corresponding C-terminally CPP-conjugated PTH(1-34). In addition, the nonaarginine sequence proved to be the only CPP capable of increasing permeation when conjugated to PTH(1-34) as compared to co-administration of CPP and PTH(1-34). This enhancement effect was, however, associated with an unacceptably low level of cell viability. In conclusion, covalent conjugation of CPPs to PTH(1-34) influenced the secondary structure, potency, and transepithelial permeation efficiency of the resulting conjugate, and hence this approach appears not to be favorable as compared to co-administration when optimizing CPP-mediated permeation of PTH(1-34) across an intestinal epithelium.