Tobacco etch virus protease retains its activity in various buffers and in the presence of diverse additives

Novel heterologously expressed protein, AjPSPLP-3, derived from Apostichopus japonicus exhibits cell proliferation and migration activities

Developing more effective bioactive ingredients of natural origin is imperative for promoting wound healing. Sea cucumbers have long enjoyed a good reputation as both food delicacies and traditional medicines. In this study, we heterogeneously expressed a Apostichopus japonicus derived novel protein AjPSPLP-3, which exhibits a theoretical molecular weight of 13.034 kDa, through fusion with maltose binding protein (MBP). AjPSPLP-3 contains a strict CXXCXC motif, nine extremely conserved cysteine residues and two highly conserved cysteine residues. The predicted structure of AjPSPLP-3 consists of random coil and nine β-sheets, Cys30-Cys67, Cys38-Cys58, Cys53-Cys90, Cys56-Cys66, and Cys81-Cys102 participating in the formation of five pairs of disulfide bonds. In vitro experiments conducted on HaCaT cells proved that AjPSPLP-3 and MBP-fused AjPSPLP-3 significantly contribute to HaCaT cells proliferation and migration without exhibiting hemolytic activity on murine erythrocytes. Specifically, treatment with 10 μmol/L MBP-fused AjPSPLP-3 protein increased the viability of HaCaT cells by 12.28 % (p < 0.001), while treatment with 10 μmol/L AjPSPLP-3 protein increased viability of HaCaT cells by 6.01 % (p < 0.01). Furthermore, wound closure of MBP-fused AjPSPLP-3 and AjPSPLP-3 were 22.51 % (p < 0.01) and 7.32 % (p < 0.05) higher than that of the control groups in HaCaT cells following 24 h of incubation.

Refinement of the Fusion Tag PagP for Effective Formation of Inclusion Bodies in Escherichia coli

Methods for efficient insoluble protein production require further exploration. PagP, an Escherichia coli outer membrane protein with high β-sheet content, could function as an efficient fusion partner for inclusion body-targeted expression of recombinant peptides. The primary structure of a given polypeptide determines to a large extent its propensity to aggregate. Herein, aggregation "hot spots" (HSs) in PagP were analyzed using the web-based software AGGRESCAN, leading to identification of a C-terminal region harboring numerous HSs. Moreover, a proline-rich region was found in the β-strands. Substitution of these prolines by residues with high β-sheet propensity and hydrophobicity significantly improved its ability to form aggregates. Consequently, the absolute yields of recombinant antimicrobial peptides Magainin II, Metchnikowin, and Andropin were increased significantly when expressed in fusion with this refined version of PagP. We describe separation of recombinant target proteins expressed in inclusion bodies fused with the tag. An artificial NHT linker peptide with three motifs was implemented for separation and purification of authentic recombinant antimicrobial peptides. IMPORTANCE Fusion tag-induced formation of inclusion bodies provides a powerful means to express unstructured or toxic proteins. For a given fusion tag, how to enhance the formation of inclusion bodies remains to be explored. Our study illustrated that the aggregation HSs in a fusion tag played important roles in mediating its insoluble expression. Efficient production of inclusion bodies could also be implemented by refining its primary structure to form a more stable β-sheet with higher hydrophobicity. This study provides a promising method for improvement of the insoluble expression of recombinant proteins.

Peptidoglycan-Targeting Staphylolytic Enzyme Lysostaphin as a Novel and Efficient Protease toward Glycine-Rich Flexible Peptide Linkers

Glycine-rich flexible peptide linkers have been widely adopted in fusion protein engineering; however, they can hardly be cleaved for the separation of fusion partners unless specific protease recognition sites are introduced. Herein, we report the use of the peptidoglycan-targeting staphylolytic enzyme lysostaphin to directly digest the glycine-rich flexible linkers of various lengths including oligoglycine linkers and (G₄S)_x linkers, without the incorporation of extra amino acids. Using His-MBP-linker-LbCpf1 as a model substrate, we show that both types of linkers could be digested by lysostaphin, and the digestion efficiency improved with increasing linker length. The enzyme LbCpf1 retained full activity after tag removal. We further demonstrated that the proteolytic activity of lysostaphin could be well maintained under different environmental conditions and in the presence of a series of chemical reagents at various concentrations that are frequently used in protein purification and stabilization. In addition, such a digestion strategy could also be applied to remove the SUMO domain linked to LwCas13a via an octaglycine linker. This study extends the applications of lysostaphin beyond an antimicrobial reagent and demonstrates its potential as a novel, efficient, and robust protease for protein engineering.

Acyl carrier protein tag can enhance tobacco etch virus protease stability and promote its covalent immobilisation

Fusion expression is widely employed to enhance the solubility of recombinant proteins. However, removal of the fusion tag is often required due to its potential impact on the structure and activity of passenger proteins. Tobacco etch virus (TEV) protease is widely used for this purpose due to its stringent sequence recognition. In the present work, fusion to the acyl carrier protein from E. coli fatty acid synthase (ACP) significantly increased the yield of recombinant soluble TEV, and the ACP tag also greatly improved TEV stability. The cleavage activity of TEV was not affected by the ACP fusion tag, and ACP-TEV retained high activity, even at unfavourable pH values. Moreover, ACP-TEV could be efficiently modified by co-expressed E. coli holo-ACP synthase (AcpS), leading to covalent attachment of 4'-phosphopantetheine (4'-PP) group to ACP. The sulfhydryl group of the long, flexible 4'-PP chain displayed high specific reactivity with iodoacetyl groups on the solid support. Thus, TEV could be immobilised effectively and conveniently via the active holo-ACP, and immobilised TEV retained high cleavage activity after a long storage period and several cycles of reuse. As a low-cost and recyclable biocatalyst, TEV immobilised by this method holds promise for biotechnological research and development. KEY POINTS: • The ACP tag greatly increased the soluble expression and stability of TEV protease. • The ACP tag did not affect the cleavage activity of TEV. • The holo-ACP Tag effectively mediated the covalent immobilisation of TEV.

Controlled co-immobilisation of proteins via 4'-phosphopantetheine-mediated site-selective covalent linkage

In Escherichia coli, acyl carrier protein (ACP) is posttranslationally converted into its active holo-ACP form via covalent linkage of 4'-phosphopantetheine (4'-PP) to residue serine-36. We found that the long flexible 4'-PP arm could react chemoselectively with the iodoacetyl group introduced on solid supports with high efficiency under mild conditions. Based on this finding, we developed site-selective immobilisation of proteins via the active holo-ACP fusion tag, independently of the physicochemical properties of the protein of interest. Furthermore, the molecular ratios of co-immobilised proteins can be manipulated because the tethering process is predominantly directed by the molar concentrations of diverse holo-ACP fusions during co-immobilisation. Conveniently tuning the molecular ratios of co-immobilised proteins allows their cooperation, leading to a highly productive multi-protein co-immobilisation system. Kinetic studies of enzymes demonstrated that α-amylase (Amy) and methyl parathion hydrolase (MPH) immobilised via active tag holo-ACP had higher catalytic efficiency (k_cat/Km) in comparison with their corresponding counterparts immobilised via the sulfhydryl groups (-SH) of these proteins. The immobilised holo-ACP-Amy also presented higher thermostability compared with free Amy. The enhanced α-amylase thermostability upon immobilisation via holo-ACP renders it more suitable for industrial application.

Combination of the mutations for improving activity of TEV protease in inclusion bodies

Tobacco etch virus protease (TEVp) is an enzymatic reagent to remove fusion tag, but additional purification steps are required for removing the TEVp after cleavage reaction is finished. Use of carrier-free and dependent TEVp immobilizates can eliminate protease contamination. In this work, we identified that, among the four constructed missense variants, the insoluble variant with the highest activity was correspondent with the soluble one tested formerly. The activities of the insoluble 15 codon variants were assayed and the variant with highest activity was selected. The K45F and/or E106G mutations have been reported on slightly improving protein stability of the wild-type TEVp, but only E106G mutation enhanced soluble production and activity of the selected TEVp variant, and it increased soluble amounts of two codon variants with the impaired folding. The decreased activity and use efficiency of the optimized TEVp variant in inclusion bodies was balanced by the determined high level production, lower leaking amounts of the protein, the enhanced resistance to the limited proteolysis mediated by protease K and trypsin, and the increased inhibition of auto-cleavage, as comparison to those of the immobilized soluble one. Thus, the TEVp construct is a potential alternate for simplifying protein purification protocols after tag-removal.

Effective production of human growth factors in Escherichia coli by fusing with small protein 6HFh8

Background

Growth factors (GFs) are signaling proteins that affect cellular processes such as growth, proliferation, and differentiation. GFs are used as cosmeceuticals, exerting anti-wrinkle, anti-aging, and whitening effects, and also as pharmaceuticals to treat wounds, growth failure, and oral mucositis. However, in mammalian and bacterial cells, low productivity and expression in inclusion bodies, respectively, of GFs does not satisfy the consumer demand. Here, we aimed to develop a bacterial expression system that produces high yields of soluble GFs that can be purified in their native forms.

Results

We present Fh8, an 8-kDa peptide from Fasciola hepatica with an N-terminal hexa-histidine (6HFh8), as a fusion partner for enhanced human GF production in recombinant Escherichia coli. The fusion partner harboring a tobacco etch virus (TEV) protease cleavage site was fused to the N-terminus of 10 human GFs: acidic and basic fibroblast growth factors (aFGF and bFGF, respectively), epidermal growth factor (EGF), human growth hormone (hGH), insulin-like growth factor 1 (IGF-1), vascular endothelial growth factor 165 (VEGF165), keratinocyte growth factor 1 (KGF-1), placental growth factor (PGF), stem cell factor (SCF), and tissue inhibitor of metalloproteinase 1 (TIMP-1). The fusion proteins were expressed in E. coli under the control of T7 promoter at three temperatures (25 °C, 30 °C, and 37 °C). All individual fusion proteins, except for SCF and TIMP-1, were successfully overexpressed in cytoplasmic soluble form at more than one temperature. Further, the original aFGF, IGF-1, EGF, and VEGF165 proteins were cleaved from the fusion partner by TEV protease. Five-liter fed-batch fermentation approaches for the 6HFh8-aFGF (lacking disulfide bonds) and 6HFh8-VEGF165 (a cysteine-rich protein) were devised to obtain the target protein at concentrations of 9.7 g/l and 3.4 g/l, respectively. The two GFs were successfully highly purified (> 99% purity). Furthermore, they exerted similar cell proliferative effects as those of their commercial equivalents.

Conclusions

We demonstrated that 6HFh8-GF fusion proteins could be overexpressed on a g/l scale in the cytoplasm of E. coli, with the GFs subsequently highly purified and maintaining their biological activity. Hence, the small protein 6HFh8 can be used for efficient mass-production of various GFs.

Optimization of solvent media to solubilize TEV protease using response surface method

Background and purpose

Tobacco etch virus (TEV) protease, a 27 KDa protein, consists of the catalytic domain of nuclear inclusion a (NIa) protein produced by Tobacco etch virus. Because of its unique sequence, TEV protease is used for purging fusion tags from proteins. It also has many advantages such as stability and activity in a board range of temperature and pH and overproduction in Escherichia coli and these benefits make this protease valuable. Despite all these benefits, TEV protease has problems like low solubility (less than 1 mg/mL). There are methods for enhancing protein solubility and in this study, the effect of additives during cell lysis was studied.

Experimental approach

Eleven different additives that made twelve different lysis buffers were used and their effect on TEV protease solubility analyzed by Plackett-Burman and response surface methodology methods.

Findings / Results

Three best effective additives on TEV solubility (L-proline, sodium selenite, and CuCl2) were selected according to software analysis and the best concentration of them was applied to optimize TEV protease solubility.

Conclusion and implications

The obtained results provided the composition of an optimum solvent for obtaining soluble TEV protease.

Rational design of a new mutant of tobacco etch virus protease in order to increase the in vitro solubility

Background and purpose:

Tobacco etch virus (TEV) protease is a protease with high sequence specificity which is useful for the cleavage of fusion proteins. A major limitation of this enzyme is its relatively poor solubility. This study aimed to investigate the effects of some suggested mutations by online tools and molecular dynamics simulation to improve the solubility of TEV protease in vitro.

Experimental approach:

We designed a rational multi-stage process to determine the solubilizing mutations of TEV protease. At the first stage, all the possible mutations were predicted using online tools such as PoPMuSiC and Eris servers, in which five mutations include N23F, N23L, Q74L, Q74V, and Q74I were suggested for further studies. In the next step, the three dimensional structure of the wild type (WT) and the best mutations were subjected to molecular dynamic simulations to evaluate the dynamic behaviour of the obtained structures. The selected mutation was introduced into the structure using site-directed mutagenesis and expressed in Escherichia coli BL21DE3. After purification, solubility and activity of the purified mutant and WT-TEV proteases were assayed.

Findings /Results:

By considering the analysis of various factors such as structural and solubility properties, one mutant, N23F, was selected for in vitro studies which led to a 1.5 times increase in the solubility compared to the WT while its activity was decreased somewhat.

Conclusion and implications:

We propose N23F mutation, according to computational and experimental analyses for TEV proteases which resulted in a 150% increase in solubility compared to the WT.

Chemoenzymatic Semisynthesis of Proteins

Protein semisynthesis-defined herein as the assembly of a protein from a combination of synthetic and recombinant fragments-is a burgeoning field of chemical biology that has impacted many areas in the life sciences. In this review, we provide a comprehensive survey of this area. We begin by discussing the various chemical and enzymatic methods now available for the manufacture of custom proteins containing noncoded elements. This section begins with a discussion of methods that are more chemical in origin and ends with those that employ biocatalysts. We also illustrate the commonalities that exist between these seemingly disparate methods and show how this is allowing for the development of integrated chemoenzymatic methods. This methodology discussion provides the technical foundation for the second part of the review where we cover the great many biological problems that have now been addressed using these tools. Finally, we end the piece with a short discussion on the frontiers of the field and the opportunities available for the future.

An Open Library of Human Kinase Domain Constructs for Automated Bacterial Expression

Kinases play a critical role in cellular signaling and are dysregulated in a number of diseases, such as cancer, diabetes, and neurodegeneration. Therapeutics targeting kinases currently account for roughly 50% of cancer drug discovery efforts. The ability to explore human kinase biochemistry and biophysics in the laboratory is essential to designing selective inhibitors and studying drug resistance. Bacterial expression systems are superior to insect or mammalian cells in terms of simplicity and cost effectiveness but have historically struggled with human kinase expression. Following the discovery that phosphatase coexpression produced high yields of Src and Abl kinase domains in bacteria, we have generated a library of 52 His-tagged human kinase domain constructs that express above 2 μg/mL of culture in an automated bacterial expression system utilizing phosphatase coexpression (YopH for Tyr kinases and lambda for Ser/Thr kinases). Here, we report a structural bioinformatics approach to identifying kinase domain constructs previously expressed in bacteria and likely to express well in our protocol, experiments demonstrating our simple construct selection strategy selects constructs with good expression yields in a test of 84 potential kinase domain boundaries for Abl, and yields from a high-throughput expression screen of 96 human kinase constructs. Using a fluorescence-based thermostability assay and a fluorescent ATP-competitive inhibitor, we show that the highest-expressing kinases are folded and have well-formed ATP binding sites. We also demonstrate that these constructs can enable characterization of clinical mutations by expressing a panel of 48 Src and 46 Abl mutations. The wild-type kinase construct library is available publicly via Addgene.

Molecular Cloning and Biochemical Characterization of Iron Superoxide Dismutase from Leishmania braziliensis

Leishmaniasis is one of the most important neglected tropical diseases, with a broad spectrum of clinical manifestations. Among the clinical manifestations of the disease, cutaneous leishmaniasis, caused by species of Leishmania braziliensis, presents wide distribution in Brazil. In this work, we performed the cloning, expression, and purification of the enzyme superoxide dismutase of Leishmania braziliensis (LbSOD-B2) considered a promising target for the search of new compounds against leishmaniasis. In vitro assays based on pyrogallol oxidation showed that LbSOD-B2 is most active around pH 8 and hydrogen peroxide is a LbSOD-B2 inhibitor at low millimolar range (IC₅₀ = 1 mM).

A simple method for recombinant protein purification using self-assembling peptide-tagged tobacco etch virus protease

Recombinant protein purification remains to be a major challenge in biotechnology and medicine. In this paper we report a simple method for recombinant protein purification using self-assembling peptide-tagged tobacco etch virus protease (TEVp). After construction of an N-terminal ELK16 peptide fusion expression vector, we expressed ELK16-TEVp fusion protein in E. coli. SDS-PAGE analysis showed that ELK16-TEVp was expressed as active protein aggregates which could be purified to 91% purity with 92% recovery by centrifugation in the presence 0.5% Triton X-100. By using His-tagged bovine interferon-γ (His-BoIFN-γ) as the substrate, we demonstrated that EKL16-TEVp had a protease activity of 1.3 × 10(4) units/mg protein with almost 100% cleavage efficiency under the optimized conditions. More importantly, EKL16-TEVp could be removed from the cleavage reaction by single-step centrifugation. After removing the His-tag by nickel-conjugated agarose bead absorption, the recombinant BoIFN-γ (rBoIFN-γ) was purified to 98.3% purity with 63% recovery. The rBoIFN-γ had an antiviral activity of 1.6 × 10(3) units/mg protein against vesicular stomatitis virus. These data suggest that ELK16-TEVp may become a universal tool for recombinant protein purification.

Tobacco Etch Virus protease: A shortcut across biotechnologies

About thirty years ago, studies on the RNA genome of Tobacco Etch Virus revealed the presence of an efficient and specific protease, called Tobacco Etch Virus protease (TEVp), that was part of the Nuclear Inclusion a (NIa) enzyme. TEVp is an efficient and specific protease of 27kDa that has become a valuable biotechnological tool. Nowadays TEVp is a unique endopeptidase largely exploited in biotechnology from industrial applications to in vitro and in vivo cellular studies. A number of TEVp mutants with different rate of cleavage, stability and specificity have been reported. Similarly, a panel of different target cleavage sites, derived from the canonical ENLYFQ-G/S site, has been established. In this review we describe these aspects of TEVp and some of its multiple applications. A particular focus is on the use and molecular biology of TEVp in living cells and organisms.

Activity of the Human Rhinovirus 3C Protease Studied in Various Buffers, Additives and Detergents Solutions for Recombinant Protein Production

Proteases are widely used to remove affinity and solubility tags from recombinant proteins to avoid potential interference of these tags with the structure and function of the fusion partner. In recent years, great interest has been seen in use of the human rhinovirus 3C protease owing to its stringent sequence specificity and enhanced activity. Like other proteases, activity of the human rhinovirus 3C protease can be affected in part by the buffer components and additives that are generally employed for purification and stabilization of proteins, hence, necessitate their removal by tedious and time-consuming procedures before proteolysis can occur. To address this issue, we examined the effect of elution buffers used for common affinity based purifications, salt ions, stability/solubility and reducing agents, and detergents on the activity of the human rhinovirus 3C protease using three different fusion proteins at 4°C, a temperature of choice for purification of many proteins. The results show that the human rhinovirus 3C protease performs better at 4°C than the frequently used tobacco etch virus protease and its activity was insensitive to most of the experimental conditions tested. Though number of fusion proteins tested is limited, we expect that these finding will facilitate the use of the human rhinovirus 3C protease in recombinant protein production for pharmaceutical and biotechnological applications.

Improved strategy for recombinant production and purification of antimicrobial peptide tachyplesin I and its analogs with high cell selectivity

Here, we report an efficient procedure for recombinant production and purification of tachyplesin I (THI) with a final yield of 17 mg/L of the culture medium. The peptide was expressed in Escherichia coli as a part of the thioredoxin fusion protein. With the use of soluble expression followed by immobilized metal-ion affinity chromatography, the recombinant protein cleavage and reversed-phase high-performance liquid chromatography, a yield of THI did not exceed 6.5 mg/L of the culture medium. Further optimization studies were carried out to improve the protein expression level and simplify purification procedure of the target peptide. To achieve better yield of the peptide, we used high-cell-density bacterial expression. The formed inclusion bodies were highly enriched with the fusion protein, which allowed us to perform direct chemical cleavage of the inclusion bodies solubilized in 6 M guanidine-HCl with subsequent selective precipitation of proteins with trifluoroacetic acid. This enabled us to avoid an extra step of purification by immobilized metal-ion affinity chromatography. The developed procedure has made it possible to obtain biologically active THI and was used for screening a number of its mutant analogs. As a result, several selective and nonhemolytic analogs were developed. Significant reduction in hemolytic activity without losing antimicrobial activity was achieved by substitution of tyrosine or isoleucine residue in the β-turn region of the molecule with hydrophilic serine. The present study affords further insight into molecular mechanism of antimicrobial action of tachyplesin and gains a better understanding of structure-activity relationships in its analogs. This is aimed at searching for novel antibiotics on the basis of antimicrobial peptides with reduced cytotoxicity.

Recombinant Passenger Proteins Can Be Conveniently Purified by One-Step Affinity Chromatography

Fusion tag is one of the best available tools to date for enhancement of the solubility or improvement of the expression level of recombinant proteins in Escherichia coli. Typically, two consecutive affinity purification steps are often necessitated for the purification of passenger proteins. As a fusion tag, acyl carrier protein (ACP) could greatly increase the soluble expression level of Glucokinase (GlcK), α-Amylase (Amy) and GFP. When fusion protein ACP-G2-GlcK-Histag and ACP-G2-Amy-Histag, in which a protease TEV recognition site was inserted between the fusion tag and passenger protein, were coexpressed with protease TEV respectively in E. coli, the efficient intracellular processing of fusion proteins was achieved. The resulting passenger protein GlcK-Histag and Amy-Histag accumulated predominantly in a soluble form, and could be conveniently purified by one-step Ni-chelating chromatography. However, the fusion protein ACP-GFP-Histag was processed incompletely by the protease TEV coexpressed in vivo, and a large portion of the resulting target protein GFP-Histag aggregated in insoluble form, indicating that the intracellular processing may affect the solubility of cleaved passenger protein. In this context, the soluble fusion protein ACP-GFP-Histag, contained in the supernatant of E. coli cell lysate, was directly subjected to cleavage in vitro by mixing it with the clarified cell lysate of E. coli overexpressing protease TEV. Consequently, the resulting target protein GFP-Histag could accumulate predominantly in a soluble form, and be purified conveniently by one-step Ni-chelating chromatography. The approaches presented here greatly simplify the purification process of passenger proteins, and eliminate the use of large amounts of pure site-specific proteases.

Engineered tobacco etch virus (TEV) protease active in the secretory pathway of mammalian cells

Tobacco etch virus protease (TEVp) is a unique endopeptidase with stringent substrate specificity. TEVp has been widely used as a purified protein for in vitro applications, but also as a biological tool directly expressing it in living cells. To adapt the protease to diverse applications, several TEVp mutants with different stability and enzymatic properties have been reported. Herein we describe the development of a novel engineered TEVp mutant designed to be active in the secretory pathway. While wild type TEVp targeted to the secretory pathway of mammalian cells is synthetized as an N-glycosylated and catalytically inactive enzyme, a TEVp mutant with selected mutations at two verified N-glycosylation sites and at an exposed cysteine was highly efficient. This mutant was very active in the endoplasmic reticulum (ER) of living cells and can be used as a biotechnological tool to cleave proteins within the secretory pathway. As an immediate practical application we report the expression of a complete functional monoclonal antibody expressed from a single polypeptide, which was cleaved by our TEVp mutant into the two antibody chains and secreted as an assembled and functional molecule. In addition, we show active TEVp mutants lacking auto-cleavage activity.

A novel method for expression and purification of authentic amyloid-β with and without (15)N labels

Amyloid-β (Aβ) is a major constituent in the senile plaques of patients with Alzheimer's disease (AD). Aβ has been intensively studied in amyloid research; however, challenges posed by data reproducibility arise from purity of synthetic Aβ and high expense for its isotope-labeling. The difficulties motivate development and optimization of recombinant Aβ (rAβ) production. Here, we report a new procedure to express and purify high quality rAβ40 from Escherichia coli. The new Aβ construct expressed insoluble Aβ fused with an N-terminal histidine-tag connected by a linker harboring TEV protease cut site. After purification and partial refolding, the fusion tag was removed by TEV protease cleavage, immobilized metal affinity chromatography (IMAC), and reversed phase-HPLC purification with a yield of 3.5 mg/L culture with and without (15)N label. The rAβ adopts classic amyloid fibrillization and is capable of binding to its clinical relevant metal ions.

Synonymous rare arginine codons and tRNA abundance affect protein production and quality of TEV protease variant

It has been identified that a TEV protease (TEVp) variant, TEVp^5M, displays improved solubility. Here, we constructed fifteen TEVp^5M variants with one or more of six rare arginine codons in the coding sequence replaced with abundant E. coli arginine codons. These codon variants expressed in either E. coli BL21 (DE3) or Rossetta (DE3) showed different solubility and activity. Supply of rare tRNAs increased the tendency of certain codon variants to form insoluble aggregates at early induction stage, as determined by the fused S-tag. About 32% increase in soluble protein production of M5 variant with four synonymously mutated arginine codons was identified in Rossetta (DE3) cells using GFP fusion reporter, comparable to that of TEVp^5M. After purification, two other codon variants from both E. coli strains exhibited less activity than TEVp^5M on cleaving the native or modified recognition sequence incorporated between GST and E. coli diaminopropionate ammonialyase by enzyme-coupled assay, whereas purified M5 variant showed activity similar to the TEVp^5M. Supply of rare tRNAs caused the decrease of activity of TEVp^5M and M5 by about 21%. Our results revealed that engineering of highly soluble TEVp variants can be achieved by the combined mutations of amino acid residues and optimization of specific rare codons, whereas simple augment of rare tRNAs abundance resulted in partial loss of activity.

Recombinant production of the amino terminal cytoplasmic region of dengue virus non-structural protein 4A for structural studies

Background

Dengue virus (DENV) is a mosquito-transmitted positive single strand RNA virus belonging to the Flaviviridae family. DENV causes dengue fever, currently the world's fastest-spreading tropical disease. Severe forms of the disease like dengue hemorrhagic fever and dengue shock syndrome are life-threatening. There is no specific treatment and no anti-DENV vaccines. Our recent data suggests that the amino terminal cytoplasmic region of the dengue virus non-structural protein 4A (NS4A) comprising amino acid residues 1 to 48 forms an amphipathic helix in the presence of membranes. Its amphipathic character was shown to be essential for viral replication. NMR-based structure-function analysis of the NS4A amino terminal region depends on its milligram-scale production and labeling with NMR active isotopes.

Methodology/Principal Findings

This report describes the optimization of a uniform procedure for the expression and purification of the wild type NS4A(1-48) peptide and a peptide derived from a replication-deficient mutant NS4A(1-48; L6E, M10E) with disrupted amphipathic nature. A codon-optimized, synthetic gene for NS4A(1-48) was expressed as a fusion with a GST-GB1 dual tag in E. coli. Tobacco etch virus (TEV) protease mediated cleavage generated NS4A(1-48) peptides without any artificial overhang. Using the described protocol up to 4 milligrams of the wild type or up to 5 milligrams of the mutant peptide were obtained from a one-liter culture. Isotopic labeling of the peptides was achieved and initial NMR spectra were recorded.

Conclusions/Significance

Small molecules targeting amphipathic helices in the related Hepatitis C virus were shown to inhibit viral replication, representing a new class of antiviral drugs. These findings highlight the need for an efficient procedure that provides large quantities of the amphipathic helix containing NS4A peptides. The double tag strategy presented in this manuscript answers these needs yielding amounts that are sufficient for comprehensive biophysical and structural studies, which might reveal new drug targets.

Engineering soluble tobacco etch virus protease accompanies the loss of stability

Tobacco etch virus protease (TEVp) is a widely used tool enzyme in biological studies. To improve the solubility of recombinant TEVp, three variants, including the double mutant (L56V/S135G), the triple mutant (T17S/N68D/I77V), and the quintuple mutant (T17S/L56V/N68D/I77V/S135G), have been developed, however, with little information on functional stability. Here we investigated the solubility and stability of the three TEVp mutants under different temperature and denaturants, and in Escherichiacoli with different cultural conditions. The quintuple mutant showed the highest solubility and thermostablity, and the double mutant was most resistant to the denaturants. The double mutant folded best in E. coli cells at 37°C with or without the co-expressed molecular chaperones GroEL, GroES and GrpE. The least soluble wild type TEVp displayed better tolerance to denaturants than the triple and the quintuple mutants. All results demonstrated that TEVp is not engineered to embody the most desirable solubility and stability by the current mutations.

Recombinant expression and purification of a tumor-targeted toxin in Bacillus anthracis

Many recombinant therapeutic proteins are purified from Escherichia coli. While expression in E. coli is easily achieved, some disadvantages such as protein aggregation, formation of inclusion bodies, and contamination of purified proteins with the lipopolysaccharides arise. Lipopolysaccharides have to be removed to prevent inflammatory responses in patients. Use of the Gram-positive Bacillus anthracis as an expression host offers a solution to circumvent these problems. Using the multiple protease-deficient strain BH460, we expressed a fusion of the N-terminal 254 amino acids of anthrax lethal factor (LFn), the N-terminal 389 amino acids of diphtheria toxin (DT389) and human transforming growth factor alpha (TGFα). The resulting fusion protein was constitutively expressed and successfully secreted by B. anthracis into the culture supernatant. Purification was achieved by anion exchange chromatography and proteolytic cleavage removed LFn from the desired fusion protein (DT389 fused to TGFα). The fusion protein showed the intended specific cytotoxicity to epidermal growth factor receptor-expressing human head and neck cancer cells. Final analyses showed low levels of lipopolysaccharides, originating most likely from contamination during the purification process. Thus, the fusion to LFn for protein secretion and expression in B. anthracis BH460 provides an elegant tool to obtain high levels of lipopolysaccharide-free recombinant protein.

Modified recombinant proteins can be exported via the Sec pathway in Escherichia coli

The correct folding of a protein is a pre-requirement for its proper posttranslational modification. The Escherichia coli Sec pathway, in which preproteins, in an unfolded, translocation-competent state, are rapidly secreted across the cytoplasmic membrane, is commonly assumed to be unfavorable for their modification in the cytosol. Whether posttranslationally modified recombinant preproteins can be efficiently transported via the Sec pathway, however, remains unclear. ACP and BCCP domain (BCCP87) are carrier proteins that can be converted into active phosphopantetheinylated ACP (holo-ACP) and biotinylated-BCCP (holo-BCCP) by AcpS and BirA, respectively. In the present study, we show that, when ACP or BCCP87 is fused to the C-terminus of secretory protein YebF or MBP, the resulting fusion protein preYebF-ACP, preYebF-BCCP87, preMBP-ACP or preMBP-BCCP87 can be modified and then secreted. Our data demonstrate that posttranslational modification of preYebF-ACP, preYebF-BCCP87 preMBP-ACP and preMBP-BCCP87 can take place in the cytosol prior to translocation, and the Sec machinery accommodates these previously modified fusion proteins. High levels of active holo-ACP and holo-BCCP87 are achieved when AcpS or BirA is co-expressed, especially when sodium azide is used to retard their translocation across the inner membrane. Our results also provide an alternative to achieve a high level of modified recombinant proteins expressed extracellularly.