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

Heterologous expression and fibrillary characterization of the microtubule-binding domain of tau associated with tauopathies

BACKGROUND

Neurofibrillary tangles (NFTs) are one of the most common pathological characteristics of Alzheimer's disease. The NFTs are mainly composed of hyperphosphorylated microtubule-associated tau. Thus, recombinant tau is urgently required for the study of its fibrillogenesis and its associated cytotoxicity.

METHODS AND RESULTS

Heterologous expression, purification, and fibrillation of the microtubule-binding domain (MBD) of tau (tauMBD) were performed. The tauMBD was heterologously expressed in E. coli. Ni-chelating affinity chromatography was then performed to purify the target protein. Thereafter, tauMBD was systematically identified using the SDS-PAGE, western blot and MALDI-TOF MS methods. The aggregation propensity of the tauMBD was explored by both the thioflavin T fluorescence and atomic force microscopy experiments.

CONCLUSIONS

The final yield of the recombinant tauMBD was ~ 20 mg L-1. It is shown that TauMBD, in the absence of an inducer, self-assembled into the typical fibrils at a faster rate than wild-type tau. Finally, the in vitro cytotoxicity of tauMBD aggregates was validated using PC12 cells. The heterologously expressed tau in this study can be further used in the investigation of the biophysical and cellular cytotoxic properties of tau.

Prokaryotic Expression and Affinity Purification of DDX3 Protein

BACKGROUND

DDX3 is a protein with RNA helicase activity that is involved in a variety of biological processes, and it is an important protein target for the development of broad-spectrum antiviral drugs, multiple cancers and chronic inflammation.

OBJECTIVES

The objective of this study is to establish a simple and efficient method to express and purify DDX3 protein in E. coli, and the recombinant DDX3 should maintain helicase activity for further tailor-made screening and biochemical function validation.

METHODS

DDX3 cDNA was simultaneously cloned into pET28a-TEV and pNIC28-Bsa4 vectors and transfected into E. coli BL21 (DE3) to compare one suitable prokaryotic expression system. The 6×His-tag was fused to the C-terminus of DDX3 to form a His-tagging DDX3 fusion protein for subsequent purification. Protein dissolution buffer and purification washing conditions were optimized. The His-tagged DDX3 protein would bind with the Ni-NTA agarose by chelation and collected by affinity purification. The 6×His-tag fused with N-terminal DDX3 was eliminated from DDX3 by TEV digestion. A fine purification of DDX3 was performed by gel filtration chromatography.

RESULTS

The recombinant plasmid pNIC28-DDX3, which contained a 6×His-tag and one TEV cleavage site at the N terminal of DDX3 sequence, was constructed for DDX3 prokaryotic expression and affinity purification based on considering the good solubility of the recombinant His-tagging DDX3, especially under 0.5 mM IPTG incubation at 18°C for 18 h to obtain more soluble DDX3 protein. Finally, the exogenous recombinant DDX3 protein was obtained with more than 95% purity by affinity purification on the Ni-NTA column and removal of miscellaneous through gel filtration chromatography. The finely-purified DDX3 still retained its ATPase activity.

CONCLUSION

A prokaryotic expression pNIC28-DDX3 system is constructed for efficient expression and affinity purification of bioactive DDX3 protein in E. coli BL21(DE3), which provides an important high-throughput screening and validation of drugs targeting DDX3.

Development of an in vitro aggregation assay for long synthetic polypeptide, amyloidogenic gelsolin fragment AGelD187N 173-242

Aggregation of the gelsolin protein fragment is the hallmark of the hereditary systemic disease gelsolin amyloidosis. As with other protein misfolding diseases, there is an urgent need for efficient disease-modifying treatment for gelsolin amyloidosis. The formation of amyloids can be reproduced by incubating the disease-causing amyloidogenic 8 kDa polypeptide, 70-residue gelsolin protein fragment, AGelD187N 173-242, in vitro and monitoring the process by thioflavin T dye. However, for screening of potential aggregation inhibitors, the required protein amounts are large and the biotechnological production of amyloidogenic proteins has many challenges. Conversely, use of shorter synthetic regions of AGelD187N 173-242 does not mimic the in vivo aggregation kinetics of full-length fragment as they have different aggregation propensity. In this study, we present an in vitro aggregation assay for full-length AGelD187N 173-242 that has been produced by solid-phase chemical synthesis and after that monomerized carefully. Chemical synthesis allows us to produce high quantities of full-length fragment efficiently and at low cost. We demonstrate that the generated aggregates are fibrillar in nature and how the purity, terminal modification, initial aggregates and seeding affect the aggregation kinetics of a synthetic gelsolin fragment. We also present sufficient quality criteria for the initial monomerized synthetic polypeptide.

Discovery of Small-Molecule Degraders for Alpha-Synuclein Aggregates

Alpha-synuclein (αSyn) species, especially the oligomers and fibers, are associated with multiple neurodegenerative diseases and cannot be directly targeted under the conventional pharmacological paradigm. Proteolysis-targeting chimera technology confers degradation of various "undruggable" targets; however, hardly any small-molecule degrader for αSyn aggregates has been reported yet. Herein, by using the probe molecule sery308 as a warhead, a series of small-molecule degraders for αSyn aggregates were designed and synthesized. Their degradation effects on αSyn aggregates were evaluated on a modified pre-formed fibril-seeding cell model. Compound 2b exhibited the highest degradation efficiency (DC₅₀ = 7.51 ± 0.53 μM) with high selectivity. Mechanistic exploration revealed that both proteasomal and lysosomal pathways were involved in this kind of degradation. Moreover, the therapeutic effects of 2b were tested on SH-SY5Y (human neuroblastoma cell line) cells and Caenorhabditis elegans. Our results provided a new class of small-molecule candidates against synucleinopathies and broadened the substrate spectrum of PROTAC-based degraders.

In vivo liquid–liquid phase separation protects amyloidogenic and aggregation‐prone peptides during overexpression in Escherichia coli

Studying pathogenic effects of amyloids requires homogeneous amyloidogenic peptide samples. Recombinant production of these peptides is challenging due to their susceptibility to aggregation and chemical modifications. Thus, chemical synthesis is primarily used to produce amyloidogenic peptides suitable for high-resolution structural studies. Here, we exploited the shielded environment of protein condensates formed via liquid-liquid phase separation (LLPS) as a protective mechanism against premature aggregation. We designed a fusion protein tag undergoing LLPS in Escherichia coli and linked it to highly amyloidogenic peptides, including β amyloids. We find that the fusion proteins form membraneless organelles during overexpression and remain fluidic-like. We also developed a facile purification method of functional Aβ peptides free of chromatography steps. The strategy exploiting LLPS can be applied to other amyloidogenic, hydrophobic, and repetitive peptides that are otherwise difficult to produce.

Hypoxia and the Kynurenine Pathway: Implications and Therapeutic Prospects in Alzheimer's Disease

Neurodegenerative diseases (NDs) like Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, Parkinson's disease, and Huntington's disease predominantly pose a significant socioeconomic burden. Characterized by progressive neural dysfunction coupled with motor or intellectual impairment, the pathogenesis of ND may result from contributions of certain environmental and molecular factors. One such condition is hypoxia, characterized by reduced organ/tissue exposure to oxygen. Reduced oxygen supply often occurs during the pathogenesis of ND and the aging process. Despite the well-established relationship between these two conditions (i.e., hypoxia and ND), the underlying molecular events or mechanisms connecting hypoxia to ND remain ill-defined. However, the relatedness may stem from the protective or deleterious effects of the transcription factor, hypoxia-inducible factor 1-alpha (HIF-1α). The upregulation of HIF-1α occurs in the pathogenesis of most NDs. The dual function of HIF-1α in acting as a "killer factor" or a "protective factor" depends on the prevailing local cellular condition. The kynurenine pathway is a metabolic pathway involved in the oxidative breakdown of tryptophan. It is essential in neurotransmission and immune function and, like hypoxia, associated with ND. Thus, a good understanding of factors, including hypoxia (i.e., the biochemical implication of HIF-1α) and kynurenine pathway activation in NDs, focusing on Alzheimer's disease could prove beneficial to new therapeutic approaches for this disease, thus the aim of this review.

Escherichia coli as an antibody expression host for the production of diagnostic proteins: significance and expression

This review article concerns the production of recombinant antibody fragments for applications mainly in the diagnostic sector. The so-called "point of care diagnostics" is very important for timely diagnosis and treatment, thus being able to save lives and resources. There is intense pressure for more accurate and less expensive rapid diagnostic tests, with a value preferably <$1. Thus, the large-scale cost-effective production of recombinant antibodies is vital. The importance of Escherichia coli toward the production of inexpensive rapid tests will be explained in this review paper. Details about the different strains of E. coli, the strategies used for the insertion and the expression of recombinant proteins, and the challenges that still exist are provided. Afterward, the importance of the expression scale and culture parameters in the final yield of the antibodies are examined. From this analysis, it appears that for good yields of recombinant antibodies, aside from appropriate gene transfer and expression, the culturing parameters are of paramount importance. Larger scale production is more favorable, mainly due to the higher cell densities that can be achieved. Yields of functional Fab fragments in the range of 10-20 mg/L are considered good in shake flasks, whereas in bioreactors can be up to 1-2 g/L. An amount of 10-500 mg of such antibody per million rapid tests is required. Despite the substantial importance of the production of the antibodies and their fragments, their downstream processing should be appropriately considered from the beginning for achieving the target value of the final rapid diagnostic tests.

Fast Purification of Recombinant Monomeric Amyloid-β from E. coli and Amyloid-β-mCherry Aggregates from Mammalian Cells

The Alzheimer's disease related peptide, Amyloid-beta (Aβ)1-40 and 1-42, has proven difficult to be purified as a recombinant monomeric protein due its expression in E. coli leading to the formation of insoluble inclusion bodies and its tendency to quickly form insoluble aggregates. A vast array of methods have been used so far, yet many have pitfalls, such as the use of tags for ease of Aβ isolation, the formation of Aβ multimers within the time frame of extraction, or the need to reconstitute Aβ from a freeze-dried state. Here, we present a rapid protocol to produce highly pure and monomeric recombinant Aβ using a one-step ion exchange purification method and to label the peptide using a maleimide dye. The washing, solubilization, and purification steps take only 3 h. We also present a protocol for the isolation of Aβ-mCherry from mammalian cells.