Expression and purification of a recombinant peptide from the Alzheimer's beta-amyloid protein for solid-state NMR

An expeditious and facile method of amyloid beta (1-42) purification

For the study of amyloid beta (Aβ) associated toxicity which is supposed to be the main pathological agent in Alzheimer's disease (AD), it is important to secure Aβ peptide with appropriate biological activity. However, commercial and synthetic Aβ often have some pitfalls like less cell toxicity, prompt aggregation and excess price, using recombinant technology, these issues can be resolved though the method also suffered from some problems such as low yield, aggregation and prolong time to purify. Thus, we previously developed an easy, economic and convenient method for Aβ42 purification using highly expressed GroES-Ubiquitin-Aβ42 fusion protein. The method was efficient, but further development was performed to improve the procedure and increase the yield. Focus was on the isolation of the fusion protein (GroES-Ubiquitin) from Aβ42 peptide. After a series of systematic testing with several chemicals, we found that methanol could precipitate efficiently the fusion protein, while the Aβ peptide was recovered in the supernatant. By this method, Aβ peptide was easily purified without tedious chromatographic steps which are main obstacles to purify the peptide in the previous method. This method yielded ~20 mg highly pure Aβ42 peptide from 1-liter bacterial culture. Different biophysical characterizations and bioactivity assays indicate that the peptide purified using this method was competitive with others which have been previously reported whereas considering the simplicity, final yield and time of purification, this method is the optimal solution.

Strategies for Optimizing the Production of Proteins and Peptides with Multiple Disulfide Bonds

Bacteria can produce recombinant proteins quickly and cost effectively. However, their physiological properties limit their use for the production of proteins in their native form, especially polypeptides that are subjected to major post-translational modifications. Proteins that rely on disulfide bridges for their stability are difficult to produce in Escherichia coli. The bacterium offers the least costly, simplest, and fastest method for protein production. However, it is difficult to produce proteins with a very large size. Saccharomyces cerevisiae and Pichia pastoris are the most commonly used yeast species for protein production. At a low expense, yeasts can offer high protein yields, generate proteins with a molecular weight greater than 50 kDa, extract signal sequences, and glycosylate proteins. Both eukaryotic and prokaryotic species maintain reducing conditions in the cytoplasm. Hence, the formation of disulfide bonds is inhibited. These bonds are formed in eukaryotic cells during the export cycle, under the oxidizing conditions of the endoplasmic reticulum. Bacteria do not have an advanced subcellular space, but in the oxidizing periplasm, they exhibit both export systems and enzymatic activities directed at the formation and quality of disulfide bonds. Here, we discuss current techniques used to target eukaryotic and prokaryotic species for the generation of correctly folded proteins with disulfide bonds.

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.

Amyloidogenicity and Cytotoxicity of a Recombinant C-Terminal His6-Tagged Aβ1-42

Aggregation of amyloid β peptide (Aβ) is closely associated with the occurrence and development of Alzheimer's disease (AD). Reproducible and detailed studies on the aggregation kinetics and structure of various aggregates have been conducted using recombinant Aβ peptides. While the His₆-tag is commonly used in the purification of recombinant proteins due to its great simplicity and affinity, there is little information on the aggregation of His₆-tagged Aβ and its corresponding cytotoxicity. Moreover, it is also unclear whether there is an effect of the His₆-tag on the amyloidogenicity and cytotoxicity of recombinant Aβ_1-42. Herein, a method to express and purify a mutant C-terminally His₆-tagged Aβ_1-42 (named as Aβ_1-42-His₆) from Escherichia coli was described. Aβ_1-42-His₆ aggregated into β-sheet-rich fibrils as shown by thioflavin T fluorescence, atomic force microscopy and circular dichroism spectroscopy. Moreover, the fibrillar recombinant Aβ_1-42-His₆ showed strong toxicity toward PC12 cells in vitro. Molecular dynamics simulations revealed that the His₆-tag contributed little to the secondary structure and intermolecular interactions, including hydrophobic interactions, salt bridges, and hydrogen bonding of the fibrillar pentamer of Aβ_1-42. This highlights the biological importance of modification on the molecular structure of Aβ. Thus, the easily purified high-quality Aβ_1-42-His₆ offers great advantages for screening aggregation inhibitors or in vitro confirmation of rationally designed drugs for the treatment of AD.

Expression, purification, and characterization of N-terminal His-tagged proteins with mutations in zinc finger 3 of zinc finger protein ZNF191(243-368)

Zinc finger protein ZNF191(243-368), the zinc finger region of ZNF191, is potentially associated with cell proliferation in hepatocellular carninoma. A His-tag expression system was used to express and purify proteins with mutations in the zinc finger 3 of ZNF191(243-368) for analysis of protein properties, structure, and functions. The purification of the His-tag fusion proteins was simpler and faster than that of the ZNF191(243-368) inclusion bodies. The properties and structures of the His-tag fusion mutant proteins were investigated using spectrographic techniques and DNA hydrolysis experiment. The His₆-tag system could be used to express ZNF191(243-368). The presence of the His₆-tag at the N-terminus of ZNF191(243-368) did not evidently affect its properties and structure. However, the site-directed mutations in zinc finger 3 affected the structure of the protein. The DNA hydrolase activity of His₆-ZF-F3/H4 suggested that four histidines in zinc finger 3 might form a structure similar to that of the active center in a hydrolase. This work reports that continuous histidines need to form a certain structure for specific functions, and provides new insights into the design of an artificial nuclease.

Highly efficient soluble expression, purification and characterization of recombinant Aβ42 fromEscherichia coli

Aggregation of amyloid-β protein (Aβ) is hypothesized to be a seminal neuropathological event in Alzheimer's disease (AD). Recombinant expression and purification of Aβ represents a common basis for investigating the molecular mechanisms of amyloid formation and toxicity. Herein, we report a novel high-yield expression and purification method for Aβ42 based on fusion with maltose binding protein (MBP) followed by the soluble polypeptide linker (NANP)₃ and a modified tobacco etch virus (TEV) cleavage site before the Aβ42. We obtained a final yield of ∼18 mg L⁻¹ of recombinant Aβ42 that was confirmed by SDS-PAGE, protein immunoblotting and MALDI-TOF. Finally, thioflavin T fluorescence and atomic force microscopy revealed that the recombinant Aβ42 aggregated into long, branched fibrils. Furthermore, the aggregates of the recombinant peptide had a strong cytotoxic effect on PC12 cells. The method described here can therefore be used to efficiently express the soluble fusion protein MBP-Aβ42 and obtain high-purity Aβ42 peptide, which can be used to understand the molecular mechanism of Aβ42 fibrillization and screen new candidate drugs for AD.

A novel high-yield expression and purification method for Aβ42 based on a fusion with maltose binding protein followed by the soluble polypeptide linker (NANP)₃ and a modified tobacco etch virus cleavage site before the Aβ42 was developed.

Effect of His-Tag on Expression, Purification, and Structure of Zinc Finger Protein, ZNF191(243-368)

Zinc finger proteins are associated with hereditary diseases and cancers. To obtain an adequate amount of zinc finger proteins for studying their properties, structure, and functions, many protein expression systems are used. ZNF191(243-368) is a zinc finger protein and can be fused with His-tag to generate fusion proteins such as His6-ZNF191(243-368) and ZNF191(243-368)-His8. The purification of His-tag protein using Ni-NTA resin can overcome the difficulty of ZNF191(243-368) separation caused by inclusion body formation. The influences of His-tag on ZNF191(243-368) properties and structure were investigated using spectrographic techniques and hydrolase experiment. Our findings suggest that insertion of a His-tag at the N-terminal or C-terminal end of ZNF191(243-368) has different effects on the protein. Therefore, an expression system should be considered based on the properties and structure of the protein. Furthermore, the hydrolase activity of ZNF191(243-368)-His8 has provided new insights into the design of biological functional molecules.

Intracellular selection of peptide inhibitors that target disulphide-bridged Aβ42 oligomers

The β-amyloid (Aβ) peptide aggregates into a number of soluble and insoluble forms, with soluble oligomers thought to be the primary factor implicated in Alzheimer's disease pathology. As a result, a wide range of potential aggregation inhibitors have been developed. However, in addition to problems with solubility and protease susceptibility, many have inadvertently raised the concentration of these soluble neurotoxic species. Sandberg et al. previously reported a β-hairpin stabilized variant of Aβ42 that results from an intramolecular disulphide bridge (A21C/A31C; Aβ42cc), which generates highly toxic oligomeric species incapable of converting into mature fibrils. Using an intracellular protein-fragment complementation (PCA) approach, we have screened peptide libraries using E. coli that harbor an oxidizing environment to permit cytoplasmic disulphide bond formation. Peptides designed to target either the first or second β-strand have been demonstrated to bind to Aβ42cc, lower amyloid cytotoxicity, and confer bacterial cell survival. Peptides have consequently been tested using wild-type Aβ42 via ThT binding assays, circular dichroism, MTT cytotoxicity assays, fluorescence microscopy, and atomic force microscopy. Results demonstrate that amyloid-PCA selected peptides function by both removing amyloid oligomers as well as inhibiting their formation. These data further support the use of semirational design combined with intracellular PCA methodology to develop Aβ antagonists as candidates for modification into drugs capable of slowing or even preventing the onset of AD.

Design and implementation of a high yield production system for recombinant expression of peptides

Background

Making peptide pharmaceuticals involves challenging processes where many barriers, which include production and manufacture, need to be overcome. A non common but interesting research area is related to peptides with intracellular targets, which opens up new possibilities, allowing the modulation of processes occurring within the cell or interference with signaling pathways. However, if the bioactive sequence requires fusion to a carrier peptide to allow access into the cell, the resulting peptide could be such a length that traditional production could be difficult. The goal of the present study was the development of a flexible recombinant expression and purification system for peptides, as a contribution to the discovery and development of these potentially new drugs.

Results

In this work, a high throughput recombinant expression and purification system for production of cell penetrating peptides in Escherichia coli has been designed and implemented. The system designed produces target peptides in an insoluble form by fusion to a hexahistidine tagged ketosteroid isomerase which is then separated by a highly efficient thrombin cleavage reaction procedure. The expression system was tested on the anticancer peptides p53pAnt and PNC27. These peptides comprise the C-terminal region and the N-terminal region of the protein p53, respectively, fused by its carboxyl terminal extreme to the cell penetrating peptide Penetratin. High yields of purified recombinant fused peptides were obtained in both cases; nevertheless, thrombin cleavage reaction was successful only for p53pAnt peptide release. The features of the system, together with the procedure developed, allow achievement of high production yields of over 30 mg of highly pure p53pAnt peptide per g of dry cell mass. It is proposed that the system could be used for production of other peptides at a similar yield.

Conclusions

This study provides a system suitable for recombinant production of peptides for scientific research, including biological assays.

Combining intracellular selection with protein-fragment complementation to derive Aβ interacting peptides

Aggregation of the β-amyloid (Aβ) peptide into toxic oligomers is considered the primary event in the pathogenesis of Alzheimer's disease. Previously generated peptides and mimetics designed to bind to amyloid fibrils have encountered problems in solubility, protease susceptibility and the population of small soluble toxic oligomers. We present a new method that opens the possibility of deriving new amyloid inhibitors. The intracellular protein-fragment complementation assay (PCA) approach uses a semi-rational design approach to generate peptides capable of binding to Aβ. Peptide libraries are based on Aβ regions responsible for instigating amyloidosis, with screening and selection occurring entirely inside Escherichia coli. Successfully selected peptides must therefore bind Aβ and recombine an essential enzyme while permitting bacterial cell survival. No assumptions are made regarding the mechanism of action for selected binders. Biophysical characterisation demonstrates that binding induces a noticeable reduction in amyloid. Therefore, this amyloid-PCA approach may offer a new pathway for the design of effective inhibitors against the formation of amyloid in general.

Large-scale production of soluble recombinant amyloid-β peptide 1-42 using cold-inducible expression system

Amyloid-β peptide 1-42 (Aβ(1-42)), the predominant form in senile plaques, plays important roles in the pathogenesis of Alzheimer's disease. Because Aβ(1-42) has aggregation-prone nature, it has been difficult to produce in a soluble state in bacterial expression systems. In this study, we modified our expression system to increase the soluble fraction of Aβ(1-42) in Escherichia coli (E. coli) cells. The expression level and solubility of recombinant Aβ(1-42) induced at the low temperature (16°C) is highly increased compared to that induced at 37°C. To optimize expression temperature, the coding region of Aβ(1-42) was constructed in a pCold vector, pCold-TF, which has a hexahistidine-tagged trigger factor (TF). Recombinant Aβ(1-42) was expressed primarily as a soluble protein using pCold vector system and purified with a nickel-chelating resin. When the toxic effect of recombinant Aβ(1-42) examined on human neuroblastoma SH-SY5Y cells, the purified Aβ(1-42) induced cell toxicity on SH-SY5Y cells. In conclusion, the system developed in this study will provide a useful method for the production of aggregation prone-peptide such as Aβ(1-42).

Chemical strategies for controlling protein folding and elucidating the molecular mechanisms of amyloid formation and toxicity

It has been more than a century since the first evidence linking the process of amyloid formation to the pathogenesis of Alzheimer's disease. During the last three decades in particular, increasing evidence from various sources (pathology, genetics, cell culture studies, biochemistry, and biophysics) continues to point to a central role for the pathogenesis of several incurable neurodegenerative and systemic diseases. This is in part driven by our improved understanding of the molecular mechanisms of protein misfolding and aggregation and the structural properties of the different aggregates in the amyloid pathway and the emergence of new tools and experimental approaches that permit better characterization of amyloid formation in vivo. Despite these advances, detailed mechanistic understanding of protein aggregation and amyloid formation in vitro and in vivo presents several challenges that remain to be addressed and several fundamental questions about the molecular and structural determinants of amyloid formation and toxicity and the mechanisms of amyloid-induced toxicity remain unanswered. To address this knowledge gap and technical challenges, there is a critical need for developing novel tools and experimental approaches that will not only permit the detection and monitoring of molecular events that underlie this process but also allow for the manipulation of these events in a spatial and temporal fashion both in and out of the cell. This review is primarily dedicated in highlighting recent results that illustrate how advances in chemistry and chemical biology have been and can be used to address some of the questions and technical challenges mentioned above. We believe that combining recent advances in the development of new fluorescent probes, imaging tools that enabled the visualization and tracking of molecular events with advances in organic synthesis, and novel approaches for protein synthesis and engineering provide unique opportunities to gain a molecular-level understanding of the process of amyloid formation. We hope that this review will stimulate further research in this area and catalyze increased collaboration at the interface of chemistry and biology to decipher the mechanisms and roles of protein folding, misfolding, and aggregation in health and disease.

Expression and purification of 15N- and 13C-isotope labeled 40-residue human Alzheimer's β-amyloid peptide for NMR-based structural analysis

Amyloid fibrils of Alzheimer's β-amyloid peptide (Aβ) are a primary component of amyloid plaques, a hallmark of Alzheimer's disease (AD). Enormous attention has been given to the structural features and functions of Aβ in amyloid fibrils and other type of aggregates in associated with development of AD. This report describes an efficient protocol to express and purify high-quality 40-residue Aβ(1-40), the most abundant Aβ in brains, for structural studies by NMR spectroscopy. Over-expression of Aβ(1-40) with glutathione S-transferase (GST) tag connected by a Factor Xa recognition site (IEGR(▾)) in Escherichia coli resulted in the formation of insoluble inclusion bodies even with the soluble GST tag. This problem was resolved by efficient recovery of the GST-Aβ fusion protein from the inclusion bodies using 0.5% (w/v) sodium lauroyl sarcosinate as solubilizing agent and subsequent purification by affinity chromatography using a glutathione agarose column. The removal of the GST tag by Factor Xa enzymatic cleavage and purification by HPLC yielded as much as ∼7 mg and ∼1.5mg of unlabeled Aβ(1-40) and uniformly (15)N- and/or (13)C-protein Aβ(1-40) from 1L of the cell culture, respectively. Mass spectroscopy of unlabeled and labeled Aβ and (1)H/(15)N HSQC solution NMR spectrum of the obtained (15)N-labeled Aβ in the monomeric form confirmed the expression of native Aβ(1-40). It was also confirmed by electron micrography and solid-state NMR analysis that the purified Aβ(1-40) self-assembles into β-sheet rich amyloid fibrils. To the best of our knowledge, our protocol offers the highest yields among published protocols for production of recombinant Aβ(1-40) samples that are amendable for an NMR-based structural analysis. The protocol may be applied to efficient preparation of other amyloid-forming proteins and peptides that are (13)C- and (15)N-labeled for NMR experiments.

Recombinant self-assembling peptides as biomaterials for tissue engineering

Synthetic nanostructures based on self-assembling systems that aim to mimic natural extracellular matrix are now being used as substrates in tissue engineering applications. Peptides are excellent starting materials for the self-assembly process as they can be readily synthesised both chemically and biologically. P₁₁-4 is an 11 amino acid peptide that undergoes triggered self-assembly to form a self-supporting hydrogel. It exists as unimers of random coil conformations in water above pH 7.5 but at low pH adopts an antiparallel β-sheet conformation. It also self-assembles under physiological conditions in a concentration-dependent manner. Here we describe an unimer P₁₁-4 production system and the use of a simple site-directed mutagenesis approach to generate a series of other P₁₁-family peptide expression vectors. We have developed an efficient purification strategy for these peptide biomaterials using a simple procedure involving chemical cleavage with cyanogen bromide then repeated filtration, lyophilisation and wash steps. We report peptide-fusion protein yields of ca. 4.64 g/L and we believe the highest reported recovery of a recombinant self-assembling peptide at 203 mg/L of pure recombinant P₁₁-4. This peptide forms a self-supporting hydrogel under physiological conditions with essentially identical physico-chemical properties to the chemically synthesised peptide. Critically it also displays excellent cytocompatibility when tested with primary human dermal fibroblasts. This study demonstrates that high levels of a series of recombinant self-assembling peptides can be purified using a simple process for applications as scaffolds in tissue engineering.

Novel semisynthetic method for generating full length beta-amyloid peptides

Bacterial expression of full length beta-amyloid (Abeta) is problematic because of toxicity and poor solubility of the expressed protein, and a strong tendency of Met35 to become oxidized in inclusion bodies. We have developed a semisynthetic method in which Abeta1-29 is expressed in bacteria as part of a fusion protein with a C-terminal intein and Chitin-Binding Domain (CBD). There is also a single residue, N-terminal Met extension. The protein, Met-Abeta1-29-Intein-CBD, is well expressed and highly water-soluble. After binding of the expressed protein to Chitin beads, treatment with sodium 2-mercapto-ethane sulfonate (MESNA) yields Met-Abeta1-29-MESNA, with a C-terminal thioester suitable for native chemical ligation. Met-Abeta1-29-MESNA is first subjected to CNBr cleavage, which removes the N-terminal Met residue, but leaves the thioester intact. We synthesized NH2-A30C-Abeta30-40, which has an N-terminal Cys residue and is the partner for native chemical ligation with Met-Abeta1-29-MESNA. Native chemical ligation proceeds rapidly and efficiently (>90% yield) to give A30C-Abeta1-40. The final step is selective desulfurization using Raney-Ni, which also proceeds rapidly and efficiently (>90% yield) to give native sequence Abeta1-40. Overall, this system is highly efficient, and can yield approximately 8-10 mg of pure Abeta1-40 from one liter of bacterial culture medium. This procedure is adaptable for producing other Abeta peptides. We have also expressed an Abeta construct bearing a point mutation associated with one type of familial Alzheimer's Disease, the Iowa mutation, i.e., Met-D23N-Abeta1-29-Intein-CBD. Since expression of the intein-containing fusion protein is robust in minimal media as well as standard enriched media, this procedure also can be readily modified for incorporating 15N or 13C labels for NMR. Future work will also include extending this system to longer Abeta peptides, such as Abeta1-42.

The recombinant amyloid-beta peptide Abeta1-42 aggregates faster and is more neurotoxic than synthetic Abeta1-42

Aggregation of the amyloid-beta (Abeta) peptide is considered a central event in the pathogenesis of Alzheimer's disease (AD). In order to bypass methodological bias related to a variety of impurities commonly present in typical preparations of synthetic Abeta, we developed a simple, generally applicable method for recombinant production of human Abeta and Abeta variants in Escherichia coli that provides milligram quantities of Abeta in very high purity and yield. Amyloid fibril formation in vitro by human Abeta1-42, the key amyloidogenic Abeta species in AD, was completed threefold faster with recombinant Abeta1-42 compared to synthetic preparations. In addition, recombinant Abeta1-42 was significantly more toxic to cultured rat primary cortical neurons, and it was more toxic in vivo, as shown by strongly increased induction of abnormal phosphorylation of tau and tau aggregation into neurofibrillary tangles in brains of P301L tau transgenic mice. We conclude that even small amounts of impurities in synthetic Abeta-including a significant fraction of racemized peptides that cannot be avoided due to the technical limitations of peptide synthesis--prevent or slow Abeta incorporation into the regular quaternary structure of growing beta-amyloid fibrils. The results validate the use of recombinant Abeta1-42 for both in vitro and in vivo studies addressing the mechanisms underlying Abeta aggregation and its related biological consequences for the pathophysiology, therapy, and prevention of AD.

The chromatography-free release, isolation and purification of recombinant peptide for fibril self-assembly

One of the major expenses associated with recombinant peptide production is the use of chromatography in the isolation and purification stages of a bioprocess. Here we report a chromatography-free isolation and purification process for recombinant peptide expressed in Escherichia coli (E. coli). Initial peptide release is by homogenization and then by enzymatic cleavage of the peptide-containing fusion protein, directly in the E. coli homogenate. Release is followed by selective solvent precipitation (SSP) to isolate and purify the peptide away from larger cell contaminants. Specifically, we expressed in E. coli the self-assembling beta-sheet forming peptide P(11)-2 in fusion to thioredoxin. Homogenate was heat treated (55 degrees C, 15 min) and then incubated with tobacco etch virus protease (TEVp) to release P(11)-2 having a native N-terminus. SSP with ethanol at room temperature then removed contaminating proteins in an integrated isolation-purification step; it proved necessary to add 250 mM NaCl to homogenate to prevent P(11)-2 from partitioning to the precipitate. This process structure gave recombinant P(11)-2 peptide at 97% polypeptide purity and 40% overall yield, without a single chromatography step. Following buffer-exchange of the 97% pure product by bind-elute chromatography into defined chemical conditions, the resulting peptide was shown to be functionally active and able to form self-assembled fibrils. To the best of our knowledge, this manuscript reports the first published process for chromatography-free recombinant peptide release, isolation and purification. The process proved able to deliver functional recombinant peptide at high purity and potentially low cost, opening cost-sensitive materials applications for peptide-based materials.

A general strategy for the bacterial expression of amyloidogenic peptides using BCL-XL-1/2 fusions

Biophysical studies on amyloidogenic and aggregation-prone peptides often require large quantities of material. However, solid-phase synthesis, handling, and purification of peptides often present challenges on these scales. Recombinant expression is an attractive alternative because of its low cost, the ability to isotopically label the peptides, and access to sequences exceeding approximately 50 residues. However, expression systems that seek to solubilize amyloidogenic peptides suffer from low yields, difficult optimizations, and isolation challenges. We present a general strategy for expressing and isolating amyloidogenic peptides in Escherichia coli by fusion to a polypeptide that drives the expression of attached peptides into bacterial inclusion bodies. This scheme minimizes toxicity during bacterial growth and enables the processing and handling of the peptides in denaturing solutions. Immobilized metal affinity chromatography, reverse phase HPLC, and cyanogen bromide cleavage are used to isolate the peptide, followed by further reverse phase HPLC, which yields milligram quantities of the purified peptide. We demonstrate that driving the peptides into inclusion bodies using fusion to BCL-XL-1/2 is a general strategy for their expression and isolation, as exemplified by the production of 11 peptides species.

Expression and purification of a recombinant amyloidogenic peptide from transthyretin for solid-state NMR spectroscopy

We describe the expression and purification of a model amyloidogenic peptide comprising residues 105-115 of human transthyretin (TTR105-115). Recombinant TTR105-115, which does not contain any non-native residues, was prepared as part of a fusion protein construct with a highly soluble B1 immunoglobulin binding domain of protein G (GB1), with typical yields of approximately 4 mg/L of uniformly (13)C,(15)N-enriched HPLC-purified peptide per liter of minimal media culture. Amyloid fibrils formed by recombinant TTR105-115 were characterized by transmission electron microscopy and solid-state NMR spectroscopy, and found to be comparable to synthetic TTR105-115 fibrils. These results establish recombinant TTR105-115 as a valuable model system for the development of new solid-state NMR techniques for the atomic-level characterization of amyloid architecture.

Production of self-assembling biomaterials for tissue engineering

Self-assembling peptide-based biomaterials are being developed for use as 3D tissue engineering scaffolds and for therapeutic drug-release applications. Chemical synthesis provides custom-made peptides in small quantities, but production approaches based upon transgenic organisms might be more cost-effective for large-scale peptide production. Long lead times for developing appropriate animal clones or plant lines and potential negative public opinion are obstacles to these routes. Microbes, particularly safe organisms used in the food industry, offer a more rapid route to the large-scale production of recombinant self-assembling biomaterials. In this review, recent advances and challenges in the recombinant production of collagen, elastin and de novo designed self-assembling peptides are discussed.

Bioproduction and characterization of a pH responsive self-assembling peptide

Peptide P(11)-4 (QQRFEWEFEQQ) was designed to self-assemble to form beta-sheets and nematic gels in the pH range 5-7 at concentrations > or =12.6 mM in water. This self-assembly is reversibly controlled by adjusting the pH of the solvent. It can also self-assemble into gels in biological media. This together with its biocompatibility and biodegradability make P(11)-4 an attractive building block for the fabrication of nanoscale materials with uses in, for example, tissue engineering. A limitation to large-scale production of such peptides is the high cost of solid phase chemical synthesis. We describe expression of peptide P(11)-4 in the bacterium Escherichia coli from constructs carrying tandem repeats of the peptide coding sequence. The vector pET31b+ was used to express P(11)-4 repeats fused to the ketosteroid isomerase protein which accumulates in easily recoverable inclusion bodies. Importantly, the use of auto-induction growth medium to enhance cell density and protein expression levels resulted in recovery of 2.5 g fusion protein/L culture in both shake flask and batch fermentation. Whole cell detergent lysis allowed recovery of inclusion bodies largely composed of the fusion protein. Cyanogen bromide cleavage followed by reverse phase HPLC allowed purification of the recombinant peptide with a C-terminal homoserine lactone (rP(11)-4(hsl)). This recombinant peptide formed pH dependent hydrogels, displayed beta-structure measured by circular dichroism and fibril formation observed by transmission electron microscopy.

A facile method for expression and purification of the Alzheimer's disease-associated amyloid beta-peptide

We report the development of a high-level bacterial expression system for the Alzheimer's disease-associated amyloid beta-peptide (Abeta), together with a scaleable and inexpensive purification procedure. Abeta(1-40) and Abeta(1-42) coding sequences together with added ATG codons were cloned directly into a Pet vector to facilitate production of Met-Abeta(1-40) and Met-Abeta(1-42), referred to as Abeta(M1-40) and Abeta(M1-42), respectively. The expression sequences were designed using codons preferred by Escherichia coli, and the two peptides were expressed in this host in inclusion bodies. Peptides were purified from inclusion bodies using a combination of anion-exchange chromatography and centrifugal filtration. The method described requires little specialized equipment and provides a facile and inexpensive procedure for production of large amounts of very pure Abeta peptides. Recombinant peptides generated using this protocol produced amyloid fibrils that were indistinguishable from those formed by chemically synthesized Abeta1-40 and Abeta1-42. Formation of fibrils by all peptides was concentration-dependent, and exhibited kinetics typical of a nucleation-dependent polymerization reaction. Recombinant and synthetic peptides exhibited a similar toxic effect on hippocampal neurons, with acute treatment causing inhibition of MTT reduction, and chronic treatment resulting in neuritic degeneration and cell loss.

Expression and purification of amyloid-beta peptides from Escherichia coli

Soluble oligomers and fibrillar deposits of amyloid beta (Abeta) are key agents of Alzheimer's disease pathogenesis. However, the mechanism of amyloid aggregation and its interaction with live cells still remain unclear requiring the preparation of large amounts of pure and different Abeta peptides. Here we describe an Escherichia coli expression system using a fusion protein to obtain either Abeta(1-40) or Abeta(1-42) by essentially the same procedure. The fusion protein uses a His-tagged intestinal fatty acid binding protein (IFABP) followed by a six-glycine linker and a Factor Xa cleavage site before the Abeta. The advantages of this system are that the fusion protein can be expressed in large amounts, that the fusion partner, IFABP, has been well characterized in terms of folding, that Abeta or mutated Abeta peptides can be obtained without any extra residues attached to the N-terminus and that the system can be used to incorporate fluorine-labeled amino acids. The incorporation of fluorine-labeled amino acids using auxotrophic strains is a useful NMR probe of side chain behavior. We obtain final yields of 4 and 3mg/L of culture for Abeta(1-40) and Abeta(1-42), respectively.

Recombinant amyloid beta-peptide production by coexpression with an affibody ligand

Background

Oligomeric and fibrillar aggregates of the amyloid β-peptide (Aβ) have been implicated in the pathogenesis of Alzheimer's disease (AD). The characterization of Aβ assemblies is essential for the elucidation of the mechanisms of Aβ neurotoxicity, but requires large quantities of pure peptide. Here we describe a novel approach to the recombinant production of Aβ. The method is based on the coexpression of the affibody protein Z_Aβ3, a selected affinity ligand derived from the Z domain three-helix bundle scaffold. Z_Aβ3 binds to the amyloidogenic central and C-terminal part of Aβ with nanomolar affinity and consequently inhibits aggregation.

Results

Coexpression of Z_Aβ3 affords the overexpression of both major Aβ isoforms, Aβ(1–40) and Aβ(1–42), yielding 4 or 3 mg, respectively, of pure ¹⁵N-labeled peptide per liter of culture. The method does not rely on a protein-fusion or -tag and thus does not require a cleavage reaction. The purified peptides were characterized by NMR, circular dichroism, SDS-PAGE and size exclusion chromatography, and their aggregation propensities were assessed by thioflavin T fluorescence and electron microscopy. The data coincide with those reported previously for monomeric, largely unstructured Aβ. Z_Aβ3 coexpression moreover permits the recombinant production of Aβ(1–42) carrying the Arctic (E22G) mutation, which causes early onset familial AD. Aβ(1–42)E22G is obtained in predominantly monomeric form and suitable, e.g., for NMR studies.

Conclusion

The coexpression of an engineered aggregation-inhibiting binding protein offers a novel route to the recombinant production of amyloidogenic Aβ peptides that can be advantageously employed to study the molecular basis of AD. The presented expression system is the first for which expression and purification of the aggregation-prone Arctic variant (E22G) of Aβ(1–42) is reported.

Structure-function relationships of pre-fibrillar protein assemblies in Alzheimer's disease and related disorders

Several neurodegenerative diseases, including Alzheimer's, Parkinson's, Huntington's and prion diseases, are characterized pathognomonically by the presence of intra- and/or extracellular lesions containing proteinaceous aggregates, and by extensive neuronal loss in selective brain regions. Related non-neuropathic systemic diseases, e.g., light-chain and senile systemic amyloidoses, and other organ-specific diseases, such as dialysis-related amyloidosis and type-2 diabetes mellitus, also are characterized by deposition of aberrantly folded, insoluble proteins. It is debated whether the hallmark pathologic lesions are causative. Substantial evidence suggests that these aggregates are the end state of aberrant protein folding whereas the actual culprits likely are transient, pre-fibrillar assemblies preceding the aggregates. In the context of neurodegenerative amyloidoses, the proteinaceous aggregates may eventuate as potentially neuroprotective sinks for the neurotoxic, oligomeric protein assemblies. The pre-fibrillar, oligomeric assemblies are believed to initiate the pathogenic mechanisms that lead to synaptic dysfunction, neuronal loss, and disease-specific regional brain atrophy. The amyloid beta-protein (Abeta), which is believed to cause Alzheimer's disease (AD), is considered an archetypal amyloidogenic protein. Intense studies have led to nominal, functional, and structural descriptions of oligomeric Abeta assemblies. However, the dynamic and metastable nature of Abeta oligomers renders their study difficult. Different results generated using different methodologies under different experimental settings further complicate this complex area of research and identification of the exact pathogenic assemblies in vivo seems daunting. Here we review structural, functional, and biological experiments used to produce and study pre-fibrillar Abeta assemblies, and highlight similar studies of proteins involved in related diseases. We discuss challenges that contemporary researchers are facing and future research prospects in this demanding yet highly important field.

Spectroscopic investigation of Ginkgo biloba terpene trilactones and their interaction with amyloid peptide Abeta(25-35)

The beneficial effects of Ginkgo biloba extract in the "treatment" of dementia are attributed to its terpene trilactone (TTL) constituents. The interactions between TTLs and amyloid peptide are believed to be responsible in preventing the aggregation of peptide. These interactions have been investigated using infrared vibrational absorption (VA) and circular dichroism (VCD) spectra. Four TTLs, namely ginkgolide A (GA), ginkgolide B (GB), ginkgolide C (GC) and bilobalide (BB) and amyloid Abeta(25-35) peptide, as a model for the full length peptide, are used in this study. GA-monoether and GA-diether have also been synthesized and investigated to help understand the role of individual carbonyl groups in these interactions. The precipitation and solubility issues encountered with the mixture of ginkgolide+Abeta peptide for VA and VCD studies were overcome using binary ethanol-D(2)O solvent mixture. The experimental VA and VCD spectra of GA, GB, GC and BB, GA-monoether and GA-diether have been analyzed using the corresponding spectra predicted with density functional theory. The time-dependent experimental VA and VCD spectra of Abeta(25-35) peptide and the corresponding experimental spectra in the presence of TTLs indicated that the effect of the TTLs in modulating the aggregation of Abeta(25-35) peptide is relatively small. Such small effects might indicate the absence of a specific interaction between the TTLs and Abeta(25-35) peptide as a major force leading to the reduced aggregation of amyloid peptides. It is possible that the therapeutic effect of G. biloba extract does not originate from direct interactions between TTLs and the Abeta(25-35) peptide and is more complex.

Purification of recombinantly expressed and cytotoxic human amyloid-beta peptide 1-42

The amyloid cascade hypothesis assigns the amyloid-beta peptide (Abeta) a central role in the pathogenesis of Alzheimer's disease (AD). Although there are strong efforts to biophysically characterize formation of Abeta aggregates and fibrils, as well as their prevention, progress is still severly hampered by the availability of tens of milligrams of recombinant Abeta(1-42). Here, we describe a reliable and easy procedure to recombinantly express and purify Abeta(1-42), which is fully cytotoxic and able to form fibrils without any further refolding steps. The yield of the procedure is 5-8 mg of tag-less peptide per liter culture volume.

Overexpression and purification of single zinc finger peptides of human zinc finger protein ZNF191

ZNF191, a new human zinc finger protein, probably relates to some hereditary diseases and cancers. To obtain structural information of zinc finger domain a convenient method for obtaining milligram quantities of each zinc finger peptide of ZNF191 is necessary. Here, we report an Escherichia coli expression system for rapid and high-level expression of zinc finger 3 and zinc finger 4 of ZNF191. The gene of zinc finger 3 or zinc finger 4 was cloned into pET31b vector to allow expression of single zinc finger peptide as a ketosteroid isomerase (KSI) fusion protein. The KSI-single zinc finger fusion protein was overexpressed in the form of inclusion body, which can be purified by washing several times using buffer solutions, and then be cleaved directly by cyanogen bromide to release single zinc finger peptide. The more than 20mg/L yield of single zinc finger peptide was achieved with more than 95% purity by using YM ultrafiltration membranes. Circular dichroism spectra of these two single zinc finger peptides titrated with Zn(2+) ions demonstrate that they have different secondary structures.

Symmetry-based constant-time homonuclear dipolar recoupling in solid state NMR

Constant-time dipolar recoupling pulse sequences are advantageous in structural studies by solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) because they yield experimental data that are relatively insensitive to radio-frequency pulse imperfections and nuclear spin relaxation processes. A new approach to the construction of constant-time homonuclear dipolar recoupling sequences is described, based on symmetry properties of the recoupled dipole-dipole interaction Hamiltonian under cyclic displacements in time with respect to the MAS sample rotation period. A specific symmetry-based pulse sequence called PITHIRDS-CT is introduced and demonstrated experimentally. (13)C NMR data for singly-(13)C-labeled amino acid powders and amyloid fibrils indicate the effectiveness of PITHIRDS-CT in measurements of intermolecular distances in solids. (15)N-detected and (13)C-detected measurements of intramolecular (15)N-(15)N distances in peptides with alpha-helical and beta-sheet structures indicate the utility of PITHIRDS-CT in studies of molecular conformations, especially measurements of backbone psi torsion angles in peptides containing uniformly (15)N- and (13)C-labeled amino acids.

Chemical ligation and cleavage on solid support facilitate recombinant peptide purification

Recombinant peptide technology offers a promising means alternative to chemical synthesis and natural extraction of peptides. The bottleneck in the process of recombinant peptide production is the paucity of efficient purification protocols to eliminate heterogeneity of the desired preparation. Here, we introduce a combination strategy to facilitate purification of recombinant therapeutic peptide via native chemical ligation and chemical cleavage on a solid support. In this study, one promising therapeutic peptide called for type-2 diabetes, GLP-1(7-37), was prepared with high yield and purity without an expensive HPLC purification. Furthermore, this method is also useful for the preparation of isotopically labeled NMR peptide samples. Hopefully, this strategy combining chemical ligation with chemical cleavage on a solid support will ameliorate the production of important recombinant pharmaceutical peptides.