Expression and purification of a recombinant antibacterial peptide, cecropin, from Escherichia coli

Development strategies and application of antimicrobial peptides as future alternatives to in-feed antibiotics

The use of in-feed antibiotics has been widely restricted due to the significant environmental pollution and food safety concerns they have caused. Antimicrobial peptides (AMPs) have attracted widespread attention as potential future alternatives to in-feed antibiotics owing to their demonstrated antimicrobial activity and environment friendly characteristics. However, the challenges of weak bioactivity, immature stability, and low production yields of natural AMPs impede practical application in the feed industry. To address these problems, efforts have been made to develop strategies for approaching the AMPs with enhanced properties. Herein, we summarize approaches to improving the properties of AMPs as potential alternatives to in-feed antibiotics, mainly including optimization of structural parameters, sequence modification, selection of microbial hosts, fusion expression, and industrially fermentation control. Additionally, the potential for application of AMPs in animal husbandry is discussed. This comprehensive review lays a strong theoretical foundation for the development of in-feed AMPs to achieve the public health globally.

A peptide encoded by a highly conserved gene belonging to the genus Streptomyces shows antimicrobial activity against plant pathogens

The genus Streptomyces has been unceasingly highlighted for the versatility and diversity of the antimicrobial agents they produce. Moreover, it is a heavily sequenced taxon in the phylum Actinobacteria. In this study, 47 sequence profiles were identified as proteins highly conserved within the genus Streptomyces. Significant hits to the 38 profiles were found in more than 2000 Streptomyces genomes, 11 of which were further conserved in more than 90% of Actinobacterial genomes analyzed. Only a few genes corresponding to these sequence profiles were functionally characterized, which play regulatory roles in the morphology and biosynthesis of antibiotics. Here a highly conserved sequence, namely, SHC-AMP (Streptomyces highly conserved antimicrobial peptide), which exhibited antimicrobial activity against bacterial and fungal plant pathogens, was reported. In particular, Arabidopsis thaliana was effectively protected against infection with Pseudomonas syringae pv. tomato DC3000 by treatment with this peptide. Results indicated the potential application of this peptide as an antimicrobial agent for control of plant diseases. Our results suggest putative target genes for controlling Streptomyces spp., including the one exhibiting antimicrobial activity against a wide range of phytopathogens.

Three-Dimensional Structure of the Antimicrobial Peptide Cecropin P1 in Dodecylphosphocholine Micelles and the Role of the C-Terminal Residues

Cecropin P1 (CP1) isolated from a large roundworm Ascaris suum, which is found in pig intestines, has been extensively studied as a model antimicrobial peptide (AMP). However, despite being a model AMP, its antibacterial mechanism is not well understood, particularly the function of its C-terminus. By using an Escherichia coli overexpression system with calmodulin as a fusion partner, we succeeded in the mass expression of recombinant peptides, avoiding toxicity to the host and degradation of CP1. The structure of the recombinant ¹⁵N- and ¹³C-labeled CP1 and its C-terminus truncated analogue in dodecylphosphocholine (DPC) micelles was determined by NMR. In this membrane-mimetic environment, CP1 formed an α-helix for almost its entire length, except for a short region at the C-terminus, and there was no evidence of a hinge, which is considered important for the expression of activity in other cecropins. Several NMR analyses showed that the entire length of CP1 was protected from water by micelles. Since the loss of the C-terminus of the analogue had little effect on the NMR structure or its interaction with the micelle, we investigated another role of the C-terminus of CP1 in its antimicrobial activity. The results showed that the C-terminal region affected the DNA-binding capacity of CP1, and this mechanism of action was also newly suggested that it contributed to the antimicrobial activity of CP1.

A hemolysin secretion pathway-based novel secretory expression platform for efficient manufacturing of tag peptides and anti-microbial peptides in Escherichia coli

BACKGROUND

Although Escherichia coli has been widely used for the expression of exogenous proteins, the secretory expression in this system is still a big obstacle. As one of the most important secretion pathways, hemolysin A (HlyA) system of E. coli can transport substrates directly from the cytoplasm to extracellular medium without the formation of any periplasmic intermediate, making it an ideal candidate for the development of the secretory production platform for exogenous proteins.

RESULTS

In this work, we developed a novel production platform, THHly, based on the HlyA secretion system, and explored its applications in the efficient preparation and quick detection of tag peptides and anti-microbial peptides. In this novel platform the signal sequence of HlyA is fused to the C-terminal of target peptide, with Tobacco Etch Virus (TEV) protease cleavage site and 6*His tag between them. Five tag peptides displayed good secretory properties in E. coli BL21 (DE3), among which T7 tag and S tag were obtained by two rounds of purification steps and TEV cleavage, and maintained their intrinsic immunogenicity. Furthermore, Cecropin A and Melittin, two different types of widely explored anti-microbial peptides, were produced likewise and verified to possess anti-microbial/anti-tumor bioactivities. No significant bacterial growth inhibition was observed during the fusion protein expression, indicating that the fusion form not only mediated the secretion but also decreased the toxicity of anti-microbial peptides (AMPs) to the host bacteria. To the best of our knowledge, this is the first report to achieve the secretory expression of these two AMPs in E. coli with considerable potential for manufacturing and industrialization purposes.

CONCLUSIONS

The results demonstrate that the HlyA based novel production platform of E. coli allowed the efficient secretory production and purification of peptides, thus suggesting a promising strategy for the industrialized production of peptide pharmaceuticals or reagents.

Easy Production of "Difficult Peptides" Using Cell-Free Protein Synthesis and a New Methionine Analogue as a Latent Peptide Cleavage Site

Aliphatic γ-chloro-α-amino acids incorporated in place of their canonical analogues through cell-free protein synthesis act as heat-labile linkers, offering a useful strategy for the straightforward production of target peptides as fusion proteins, from which the targets are readily released. Until now, the natural abundance of aliphatic amino acids in peptides has limited the scope of the method, as it leads to undesired cleavage sites in synthesized products, but here the authors report the development of a new cleavable chloro amino acid that incorporates in place of the relatively rare amino acid methionine, thus greatly expanding the scope of producible targets. This new strategy is employed for simplified peptide synthesis with a methionine-free fusion partner, allowing single-site incorporation of the cleavable linker for clean release and easy purification of the target peptide. Its utility is demonstrated through the straightforward preparation of two peptides reported to be challenging targets and not accessible through standard solid-phase chemical methodologies, as well as analogues.

Construction of a Tandem Repeat Peptide Sequence with Pepsin Cutting Sites to Produce Recombinant α-Melanocyte-Stimulating Hormone

The production of α-melanocyte-stimulating hormone (α-MSH), a peptide hormone composed of 13 amino acids, is attempted by recombinant expression using E. coli as the host. To achieve this aim, a synthetic gene containing eight tandem repeats of msh gene (8msh) was designed for ribosomal synthesis of 8 α-MSH. The merit of the strategy is to diminish the peptide toxicity against the host cell and to achieve a higher production yield. Pepsin cleavage sites are introduced between the peptides for enzymatic proteolysis to obtain the monomeric peptide of α-MSH. The constructed plasmid was transformed into different strains of E. coli hosts, and E. coli XL1-Blue with gene 8msh revealed the highest yield of 8 α-MSH. Although 8 α-MSH was fractionalized in the insoluble pellets after cell lysis, pepsin cleavage was able to produce soluble α-MSH peptide, as analyzed and confirmed by mass spectrometry and peptide activity assays. The production of α-MSH was quantified using HPLC with a yield of 42.9 mg/L of LB culture. This study demonstrates the feasibility of producing α-MSH using recombinant expression of tandem repeat gene. The production procedure involves minimal post-treatment and processing and can be scaled up for industrial application.

Recombinant expression and coexpression of oyster defensin and proline-rich peptide in Komagataella phaffii

Proline-rich peptide (CgPrp) and defensin (CgDef), oyster (Crassostrea gigas)-originated antimicrobial peptides (AMPs), were produced by the recombinant technique in Komagataella phaffii GS115 cells. For this purpose, the nucleotide sequences encoding the CgPrp and CgDef peptides were synthesized by the recursive PCR technique, and ligated in pPICZaA expression vector. Additionally, the expression cassettes of pPICZαA-CgDef and pPICZαA-CgPrp were combined using in vitro multimer ligation strategy to construct the coexpression vector pPICZaA-CgPrp-CgDef. The expression and coexpression vectors transformed into K. phaffii GS115 cells by electroporation. At the end of the 0.5% methanol-induced expression stage for 96 h, the recombinant peptides were purified from the culture medium. The concentrations of purified peptides were changed between 1.05 and 1.21 mg/L. The recombinant peptides successfully inhibited the growth of tested Gram-positive bacterial strains belonging to Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Listeria monocytogenes, and Bacillus cereus. The minimum inhibitory concentrations (MIC) of recombinant CgPrp, CgDef, and CgPrp-CgDef peptides against tested bacteria were in the range of 12.50-25.00, 18.75-75.00, and 5.80-11.60 pg/μl, respectively. The results of the study proved that the recombinant CgPrp, CgDef, and CgPrp-CgDef peptides expressed in K. phaffii might have good potential for the inhibition of common Gram-positive pathogenic bacteria, including drug-resistant MRSA.

Biotechnological Insights on the Expression and Production of Antimicrobial Peptides in Plants

The emergence of drug-resistant pathogens poses a serious critical threat to global public health and requires immediate action. Antimicrobial peptides (AMPs) are a class of short peptides ubiquitously found in all living forms, including plants, insects, mammals, microorganisms and play a significant role in host innate immune system. These peptides are considered as promising candidates to treat microbial infections due to its distinct advantages over conventional antibiotics. Given their potent broad spectrum of antimicrobial action, several AMPs are currently being evaluated in preclinical/clinical trials. However, large quantities of highly purified AMPs are vital for basic research and clinical settings which is still a major bottleneck hindering its application. This can be overcome by genetic engineering approaches to produce sufficient amount of diverse peptides in heterologous host systems. Recently plants are considered as potential alternatives to conventional protein production systems such as microbial and mammalian platforms due to their unique advantages such as rapidity, scalability and safety. In addition, AMPs can also be utilized for development of novel approaches for plant protection thereby increasing the crop yield. Hence, in order to provide a spotlight for the expression of AMP in plants for both clinical or agricultural use, the present review presents the importance of AMPs and efforts aimed at producing recombinant AMPs in plants for molecular farming and plant protection so far.

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.

A eukaryotic expression strategy for producing the novel antimicrobial peptide PRW4

The antimicrobial peptide PMAP-36 is a cationic peptide derived from porcine myeloid. The N-terminally paired lysine of PMAP-36 was substituted with tryptophan, and the C-terminal hydrophobic tail was deleted, thereby obtaining the antimicrobial peptide PRW4. PRW4 is a α-helical antimicrobial peptide with broad-spectrum antimicrobial activity. In this study, PRW4 was fused to the 6× His-Trx, and the fusion protein was successfully expressed in Pichia pastoris GS115 from the vector pPICZαA. The maximal induction of recombinant protein occurred in the presence of 1% methanol after 96 h at pH 6.0. After purification by a Ni-NTA resin column and digestion by enterokinase protease, 15 mg of recombinant PRW4 with a purity of 90% was obtained from 1 L of fermentation culture. The results indicated that recombinant PRW4 had similar antimicrobial activity as synthetic PRW4 against bacteria such as Escherichia coli ATCC 25922, Escherichia coli UB 1005, Salmonella typhimurium C7731, Salmonella typhimurium 7913, Salmonella typhimurium ATCC 14028, Staphylococcus aureus ATCC 29213, Staphylococcus epidermidis ATCC 12228, and Streptococcus faecalis ATCC 29212. We have successfully expressed PRW4 in P. pastoris, and this work provides a reference for the production of modified antimicrobial peptides in P. pastoris.

Study on Cecropin B2 Production via Construct Bearing Intein Oligopeptide Cleavage Variants

In this study, genetic engineering was applied to the overexpression of the antimicrobial peptide (AMP) cecropin B2 (cecB2). pTWIN1 vector with a chitin-binding domain (CBD) and an auto-cleavage Ssp DnaB intein (INT) was coupled to the cecB2 to form a fusion protein construct and expressed via Escherichia coli ER2566. The cecB2 was obtained via the INT cleavage reaction, which was highly related to its adjacent amino acids. Three oligopeptide cleavage variants (OCVs), i.e., GRA, CRA, and SRA, were used as the inserts located at the C-terminus of the INT to facilitate the cleavage reaction. SRA showed the most efficient performance in accelerating the INT self-cleavage reaction. In addition, in order to treat the INT as a biocatalyst, a first-order rate equation was applied to fit the INT cleavage reaction. A possible inference was proposed for the INT cleavage promotion with varied OCVs using a molecular dynamics (MD) simulation. The production and purification via the CBD-INT-SRA-cecB2 fusion protein resulted in a cecB2 yield of 58.7 mg/L with antimicrobial activity.

Identification of steroid C27 monooxygenase isoenzymes involved in sterol catabolism and stepwise pathway engineering of Mycobacterium neoaurum for improved androst-1,4-diene-3,17-dione production

Cholesterol oxidase, steroid C27 monooxygenase and 3-ketosteroid-Δ1-dehydrogenase are key enzymes involved in microbial catabolism of sterols. Here, three isoenzymes of steroid C27 monooxygenase were firstly characterized from Mycobacterium neoaurum as the key enzyme in sterol C27-hydroxylation. Among these three isoenzymes, steroid C27 monooxygenase 2 exhibits the strongest function in sterol catabolism. To improve androst-1,4-diene-3,17-dione production, cholesterol oxidase, steroid C27 monooxygenase 2 and 3-ketosteroid-Δ1-dehydrogenase were coexpressed to strengthen the metabolic flux to androst-1,4-diene-3,17-dione, and 3-ketosteroid 9α-hydroxylase, which catalyzes the androst-1,4-diene-3,17-dione catabolism, was disrupted to block the androst-1,4-diene-3,17-dione degradation pathway in M. neoaurum JC-12. Finally, the recombinant strain JC-12S2-choM-ksdd/ΔkshA produced 20.1 g/L androst-1,4-diene-3,17-dione, which is the highest reported production with sterols as substrate. Therefore, this work is hopes to pave the way for efficient androst-1,4-diene-3,17-dione production through metabolic engineering.

Biocontrol of Brettanomyces/Dekkera bruxellensis in alcoholic fermentations using saccharomycin-overproducing Saccharomyces cerevisiae strains

Microbial contamination of alcoholic fermentation processes (e.g. winemaking and fuel-ethanol production) is a serious problem for the industry since it may render the product unacceptable and/or reduce its productivity, leading to large economic losses. Brettanomyces/Dekkera bruxellensis is one of the most dangerous microbial contaminant of ethanol industrial fermentations. In the case of wine, this yeast species can produce phenolic compounds that confer off-flavours to the final product. In fuel-ethanol fermentations, D. bruxellensis is a persistent contaminant that affects ethanol yields and productivities. We recently found that Saccharomyces cerevisiae secretes a biocide, which we named saccharomycin, composed of antimicrobial peptides (AMPs) derived from the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Saccharomycin is active against several wine-related yeast species, namely D. bruxellensis. However, the levels of saccharomycin naturally secreted by S. cerevisiae during alcoholic fermentation are not sufficient to ensure the complete death of D. bruxellensis. Therefore, the aim of the present work was to construct genetically modified S. cerevisiae strains to overproduce these GAPDH-derived AMPs. The expression levels of the nucleotides sequences encoding the AMPs were evaluated in the modified S. cerevisiae strains by RT-qPCR, confirming the success of the recombinant approach. Furthermore, we confirmed by immunological tests that the modified S. cerevisiae strains secreted higher amounts of the AMPs by comparison with the non-modified strain, inducing total death of D. bruxellensis during alcoholic fermentations.

Enhanced cecropin B2 production via chitin-binding domain and intein self-cleavage system

In this study, various constructs and hosts were used to produce high levels of cecropin B2 (cecB2). To mitigate cecB2's toxic inhibition of host cells, various cecB2 constructs were built. Results showed that the combination of a chitin-binding domain and an intein self-cleavage motif in front of cecropin B2, without a His-tag, was best for cecB2 expression. E. coli ER2566 was the best host, and 2YT was the best medium for cultivation. Under these conditions, a cecB2 yield of 98.2 mg/L could be obtained after purification. The purified cecB2 expressed a wide antimicrobial effect on most Gram-negative strains, including multidrug-resistant Acinetobactor baumannii and Staphylococcus aureus. This study provides a systematic approach to the efficient production of the antimicrobial peptide (AMP) cecB2 via the recombinant E. coli process, which is expected to be an efficient way for the production of other AMPs.

Rapid and efficient production of cecropin A antibacterial peptide in Escherichia coli by fusion with a self-aggregating protein

BACKGROUND

Cecropin A (CeA), a natural cationic antimicrobial peptide, exerts potent antimicrobial activity against a broad spectrum of Gram-positive and Gram-negative bacteria, making it an attractive candidate substitute for antimicrobials. However, the low production rate and cumbersome, expensive processes required for both its recombinant and chemical synthesis have seriously hindered the exploitation and application of CeA. Here, we utilized a short β-structured self-aggregating protein, ELK16, as a fusion partner of CeA, which allowed the efficient production of high-purity CeA antibacterial peptide with a simple inexpensive process.

RESULTS

In this study, three different approaches to the production of CeA peptide were investigated: an affinity tag (His-tag)-fused protein expression system (AT-HIS system), a cell-free protein expression system (CF system), and a self-assembling peptide (ELK16)-fused protein expression system (SA-ELK16 system). In the AT-HIS and CF systems, the CeA peptide was obtained with purities of 92.1% and 90.4%, respectively, using one or more affinity-chromatographic purification steps. The procedures were tedious and costly, with CeA yields of only 0.41 and 0.93 μg/mg wet cell weight, respectively. Surprisingly, in the SA-ELK16 system, about 6.2 μg/mg wet cell weight of high-purity (approximately 99.8%) CeA peptide was obtained with a simple low-cost process including steps such as centrifugation and acetic acid treatment. An antimicrobial test showed that the high-purity CeA produced in this study had the same antimicrobial activity as synthetic CeA peptide.

CONCLUSIONS

In this study, we designed a suitable expression system (SA-ELK16 system) for the production of the antibacterial peptide CeA and compared it with two other protein expression systems. A high yield of high-purity CeA peptide was obtained with the SA-ELK16 system, which greatly reduced the cost and time required for downstream processing. This system may provide a platform for the laboratory scale production of the CeA antibacterial peptide.

Expression, Purification, and Characterization of a Novel Hybrid Peptide with Potent Antibacterial Activity

The hybrid peptide cecropin A (1⁻8)⁻LL37 (17⁻30) (C⁻L), derived from the sequence of cecropin A (C) and LL-37 (L), showed significantly increased antibacterial activity and minimized hemolytic activity than C and L alone. To obtain high-level production of C⁻L, the deoxyribonucleic acid sequence encoding C⁻L with preferred codons was cloned into pET-SUMO to construct a fusion expression vector, and overexpressed in Escherichia coli (E. coli) BL21 (DE3). The maximum fusion protein (92% purity) was obtained with the yield of 89.14 mg/L fermentation culture after purification with Ni-NTA Sepharose column. The hybrid C⁻L was cleaved from the fusion protein by SUMO-protease, and 17.54 mg/L pure active C⁻L was obtained. Furthermore, the purified C⁻L showed identical antibacterial and hemolytic activity to synthesized C⁻L. Stability analysis results exhibited that the activity of C⁻L changed little below 80 °C for 20 min, but when the temperature exceeded 80 °C, a significant decrease was observed. Varying the pH from 5.0 to 10.0 did not appear to influence the activity of C⁻L, however, pH below 4.0 decreased the antibacterial activity of C⁻L rapidly. Under the challenge of several proteases (pepsin, trypsin, and proteinase K), the functional activity of C⁻L was maintained over 50%. In summary, this study not only supplied an effective approach for high-level production of hybrid peptide C⁻L, but paved the way for its further exploration in controlling infectious diseases of farm animals or even humans.

Efficient biosynthesis of a Cecropin A-melittin mutant in Bacillus subtilis WB700

The efficient production of antimicrobial peptides (AMPs) for clinical applications has attracted the attention of the scientific community. To develop a novel microbial cell factory for the efficient biosynthesis of a cecropin A-melittin mutant (CAM-W), a recombinant Bacillus subtilis WB700 expression system was genetically modified with a novel vector, including a fusion gene encoding CAM-W, the autoprotease EDDIE and the signal peptide SacB under the control of the maltose-inducible promoter P_glv. A total of 159 mg of CAM-W was obtained from 1 L of fermentation supernatant. The purified CAM-W showed a consistent size with the expected molecular weight of 3.2 kDa. Our findings suggest that this novel expression system can be used as a powerful tool for the efficient production of CAM-W.

An anionic defensin from Plutella xylostella with potential activity against Bacillus thuringiensis

Insect defensins, are cationic peptides that play an important role in immunity against microbial infection. In the present study, an anionic defensin from Plutella xylostella, (designated as PxDef) was first cloned and characterized. Amino acid sequence analysis showed that the mature peptide owned characteristic six-cysteine motifs with predicted isoelectric point of 5.57, indicating an anionic defensin. Quantitative real-time polymerase chain reaction analysis showed that PxDef was significantly induced in epidermis, fat body, midgut and hemocytes after injection of heat-inactivated Bacillus thuringiensis, while such an induction was delayed by the injection of live B. thuringiensis in the 4th instar larvae of P. xylostella. Knocking down the expression of nuclear transcription factor Dorsal in P. xylostella by RNA interference significantly decreased the mRNA level of PxDef, and increased the sensitivity of P. xylostella larvae to the infection by live B. thuringiensis. The purified recombinant mature peptide (PxDef) showed higher activity against Gram-positive bacteria, with the minimum inhibition concentrations of 1.6 and 2.6 µM against B. thuringiensis and Bacillus subtilis, respectively. To our knowledge, this is the first report about an anionic PxDef, which may play an important role in the immune system of P. xylostella against B. thuringiensis.

A mutant form of 3-ketosteroid-Δ1-dehydrogenase gives altered androst-1,4-diene-3, 17-dione/androst-4-ene-3,17-dione molar ratios in steroid biotransformations by Mycobacterium neoaurum ST-095

Mycobacterium neoaurum ST-095 and its mutant M. neoaurum JC-12, capable of transforming phytosterol to androst-1,4-diene-3,17-dione (ADD) and androst-4-ene-3,17-dione (AD), produce very different molar ratios of ADD/AD. The distinct differences were related to the enzyme activity of 3-ketosteroid-Δ1-dehydrogenase (KSDD), which catalyzes the C1,2 dehydrogenation of AD to ADD specifically. In this study, by analyzing the primary structure of KSDDI (from M. neoaurum ST-095) and KSDDII (from M. neoaurum JC-12), we found the only difference between KSDDI and KSDDII was the mutation of Val366 to Ser366. This mutation directly affected KSDD enzyme activity, and this result was confirmed by heterologous expression of these two enzymes in Bacillus subtilis. Assay of the purified recombinant enzymes showed that KSDDII has a higher C1,2 dehydrogenation activity than KSDDI. The functional difference between KSDDI and KSDDII in phytosterol biotransformation was revealed by gene disruption and complementation. Phytosterol transformation results demonstrated that ksdd  I and ksdd  II gene disrupted strains showed similar ADD/AD molar ratios, while the ADD/AD molar ratios of the ksdd  I and ksdd  II complemented strains were restored to their original levels. These results proved that the different ADD/AD molar ratios of these two M. neoaurum strains were due to the differences in KSDD. Finally, KSDD structure analysis revealed that the Val366Ser mutation could possibly play an important role in stabilizing the active center and enhancing the interaction of AD and KSDD. This study provides a reliable theoretical basis for understanding the structure and catalytic mechanism of the Mycobacteria KSDD enzyme.

Expression and purification of toxic anti-breast cancer p28-NRC chimeric protein

BACKGROUND

Chimeric proteins consisting of a targeting moiety and a cytotoxic moiety are now under intense research focus for targeted therapy of cancer. Here, we report cloning, expression, and purification of such a targeted chimeric protein made up of p28 peptide as both targeting and anticancer moiety fused to NRC peptide as a cytotoxic moiety. However, since the antimicrobial activity of the NRC peptide would intervene expression of the chimeric protein in Escherichia coli, we evaluated the effects of two fusion tags, that is, thioredoxin (Trx) and 6x-His tags, and various expression conditions, on the expression of p28-NRC chimeric protein.

MATERIALS AND METHODS

In order to express the chimeric protein with only 6x-His tag, pET28 expression plasmid was used. Cloning in pET32 expression plasmid was performed to add both Trx and 6x-His tags to the chimeric protein. Expression of the chimeric protein with both plasmids was evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis following optimization of expression conditions and host strains.

RESULTS

Expression of the chimeric protein in pET28a was performed. However, expression yield of the chimeric protein was low. Optimization of culture conditions and host strains led to reasonable expression yield of the toxic chimeric protein in pET32a vector. In cases of both plasmids, approximately 10 kDa deviation of the apparent molecular weight from the theoretical one was seen in SDS-PAGE of purified chimeric proteins.

CONCLUSIONS

The study leads to proper expression and purification yield of p28-NRC chimeric protein with Trx tag following optimizing culture conditions and host strains.

Lipopolysaccharide-bound structure of the antimicrobial peptide cecropin P1 determined by nuclear magnetic resonance spectroscopy

Antimicrobial peptides (AMPs) are components of the innate immune system and may be potential alternatives to conventional antibiotics because they exhibit broad-spectrum antimicrobial activity. The AMP cecropin P1 (CP1), isolated from nematodes found in the stomachs of pigs, is known to exhibit antimicrobial activity against Gram-negative bacteria. In this study, we investigated the interaction between CP1 and lipopolysaccharide (LPS), which is the main component of the outer membrane of Gram-negative bacteria, using circular dichroism (CD) and nuclear magnetic resonance (NMR). CD results showed that CP1 formed an α-helical structure in a solution containing LPS. For NMR experiments, we expressed (15) N-labeled and (13) C-labeled CP1 in bacterial cells and successfully assigned almost all backbone and side-chain proton resonance peaks of CP1 in water for transferred nuclear Overhauser effect (Tr-NOE) experiments in LPS. We performed (15) N-edited and (13) C-edited Tr-NOE spectroscopy for CP1 bound to LPS. Tr-NOE peaks were observed at the only C-terminal region of CP1 in LPS. The results of structure calculation indicated that the C-terminal region (Lys15-Gly29) formed the well-defined α-helical structure in LPS. Finally, the docking study revealed that Lys15/Lys16 interacted with phosphate at glucosamine I via an electrostatic interaction and that Ile22/Ile26 was in close proximity with the acyl chain of lipid A.

Antibacterial Peptide CecropinB2 Production via Various Host and Construct Systems

Cecropin is a cationic antibacterial peptide composed of 35-39 residues. This peptide has been identified as possessing strong antibacterial activity and low toxicity against eukaryotic cells, and it has been claimed that some types of the cecropin family of peptides are capable of killing cancer cells. In this study, the host effect of cloning antibacterial peptide cecropinB2 was investigated. Three different host expression systems were chosen, i.e., Escherichia coli, Bacillus subtilis and Pichia pastoris. Two gene constructs, cecropinB2 (cecB2) and intein-cecropinB2 (INT-cecB2), were applied. Signal peptide and propeptide from Armigeres subalbatus were also attached to the gene construct. The results showed that the best host for cloning cecropinB2 was P. pastoris SMD1168 harboring the gene of pGAPzαC-prepro-cecB2 via Western blot confirmation. The cecropinB2 that was purified using immobilized-metal affinity chromatography resin showed strong antibacterial activity against the Gram-negative strains, including the multi-drug-resistant bacteria Acinetobacter baumannii.

Cecropins from Plutella xylostella and Their Interaction with Metarhizium anisopliae

Cecropins are the most potent induced peptides to resist invading microorganisms. In the present study, two full length cDNA encoding cecropin2 (Px-cec2) and cecropin3 (Px-cec3) were obtained from P. xylostella by integrated analysis of genome and transcriptome data. qRT-PCR analysis revealed the high levels of transcripts of Px-cecs (Px-cec1, Px-cec2 and Px-cec3) in epidermis, fat body and hemocytes after 24, 30 and 36 h induction of Metarhizium anisopliae, respectively. Silencing of Spätzle and Dorsal separately caused the low expression of cecropins in the fat body, epidermis and hemocytes, and made the P.xylostella larvae more susceptible to M. anisopliae. Antimicrobial assays demonstrated that the purified recombinant cecropins, i.e., Px-cec1, Px-cec2 and Px-cec3, exerted a broad spectrum of antimicrobial activity against fungi, as well as Gram-positive and Gram-negative bacteria. Especially, Px-cecs showed higher activity against M. anisopliae than another selected fungi isolates. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that cecropins exerted the vital morphological alterations to the spores of M. anisopliae. Based on our results, cecropins played an imperative role in resisting infection of M. anisopliae, which will provide the foundation of biological control of insect pests by using cecorpins as a target in the future.

Soluble expression, purification and functional characterization of a coil peptide composed of a positively charged and hydrophobic motif

A de novo heterodimeric coiled-coil system formed by the association of two synthetic peptides, the Ecoil and Kcoil, has been previously designed and proven to be an excellent and versatile tool for various biotechnology applications. However, based on the challenges encountered during its chemical synthesis, the Kcoil peptide has been designated as a "difficult peptide". In this study, we explore the expression of the Kcoil peptide by a bacterial system as well as its subsequent purification. The maximum expression level was observed when the peptide was fused to thioredoxin and the optimized purification process consisted of three chromatographic steps: immobilized-metal affinity chromatography followed by cation-exchange chromatography and, finally, a reverse-phase high-performance liquid chromatography. This entire process led to a final volumetric production yield of 1.5 mg of pure Kcoil peptide per liter of bacterial culture, which represents a significant step towards the cost-effective production and application of coiled-coil motifs. Our results thus demonstrate for the first time that bacterial production is a viable alternative to the chemical synthesis of de novo designed coil peptides.

Key enzymes and proteins of crop insects as candidate for RNAi based gene silencing

RNA interference (RNAi) is a mechanism of homology dependent gene silencing present in plants and animals. It operates through 21-24 nucleotides small RNAs which are processed through a set of core enzymatic machinery that involves Dicer and Argonaute proteins. In recent past, the technology has been well appreciated toward the control of plant pathogens and insects through suppression of key genes/proteins of infecting organisms. The genes encoding key enzymes/proteins with the great potential for developing an effective insect control by RNAi approach are actylcholinesterase, cytochrome P450 enzymes, amino peptidase N, allatostatin, allatotropin, tryptophan oxygenase, arginine kinase, vacuolar ATPase, chitin synthase, glutathione-S-transferase, catalase, trehalose phosphate synthase, vitellogenin, hydroxy-3-methylglutaryl coenzyme A reductase, and hormone receptor genes. Through various studies, it is demonstrated that RNAi is a reliable molecular tool which offers great promises in meeting the challenges imposed by crop insects with careful selection of key enzymes/proteins. Utilization of RNAi tool to target some of these key proteins of crop insects through various approaches is described here. The major challenges of RNAi based insect control such as identifying potential targets, delivery methods of silencing trigger, off target effects, and complexity of insect biology are very well illustrated. Further, required efforts to address these challenges are also discussed.

Recombinant expression of antimicrobial peptides using a novel self-cleaving aggregation tag in Escherichia coli

Antimicrobial peptides (AMPs) are part of the innate immune system of complex multicellular organisms. Despite the fact that AMPs show great potential as a novel class of antibiotics, the lack of a cost-effective means for their mass production limits both basic research and clinical use. In this work, we describe a novel expression system for the production of antimicrobial peptides in Escherichia coli by combining ΔI-CM mini-intein with the self-assembling amphipathic peptide 18A to drive the formation of active aggregates. Two AMPs, human β-defensin 2 and LL-37, were fused to the self-cleaving tag and expressed as active protein aggregates. The active aggregates were recovered by centrifugation and the intact antimicrobial peptides were released into solution by an intein-mediated cleavage reaction in cleaving buffer (phosphate-buffered saline supplemented with 40 mmol/L Bis–Tris, 2 mmol/L EDTA, pH 6.2). The peptides were further purified by cation-exchange chromatography. Peptides yields of 0.82 ± 0.24 and 0.59 ± 0.11 mg/L were achieved for human β-defensin 2 and LL-37, respectively, with demonstrated antimicrobial activity. Using our expression system, intact antimicrobial peptides were recovered by simple centrifugation from active protein aggregates after the intein-mediated cleavage reaction. Thus, we provide an economical and efficient way to produce intact antimicrobial peptides in E. coli.

Current scenario of peptide-based drugs: the key roles of cationic antitumor and antiviral peptides

Cationic antimicrobial peptides (AMPs) and host defense peptides (HDPs) show vast potential as peptide-based drugs. Great effort has been made in order to exploit their mechanisms of action, aiming to identify their targets as well as to enhance their activity and bioavailability. In this review, we will focus on both naturally occurring and designed antiviral and antitumor cationic peptides, including those here called promiscuous, in which multiple targets are associated with a single peptide structure. Emphasis will be given to their biochemical features, selectivity against extra targets, and molecular mechanisms. Peptides which possess antitumor activity against different cancer cell lines will be discussed, as well as peptides which inhibit virus replication, focusing on their applications for human health, animal health and agriculture, and their potential as new therapeutic drugs. Moreover, the current scenario for production and the use of nanotechnology as delivery tool for both classes of cationic peptides, as well as the perspectives on improving them is considered.

Expression of Hsp70 in the mud crab, Scylla paramamosain in response to bacterial, osmotic, and thermal stress

Hsp70 is involved in immune responses against infectious pathogens, thermal, and osmotic stress. To understand the immune defense mechanisms of the mud crab Scylla paramamosain, genomic DNA, transcript level and antimicrobial activities of Hsp70 were analyzed. Genomic DNA sequence analysis revealed one intron in this gene. Furthermore, six SNPs were detected by direct sequencing from 30 samples in this study. Hsp70 mRNA was expressed in almost all tissues examined. By using the quantitative real-time PCR, the expression level of Hsp70 in hemocytes showed a clear time-dependent expression pattern during the 96 h after stimulated by Vibrio alginolyticus. Then, recombinant Hsp70 was obtained by using the bacterial expression system, but no obvious antimicrobial activity has been found for the protein in the antimicrobial tests. After osmotic stress, the expression of Hsp70 in hemocytes showed this gene was induced by the high salinity (30 ‰) for at least 96 h. Hsp70 mRNA expression in hemocytes was analyzed after thermal stress at 6 h, the highest and the lowest expression level of Hsp70 was observed at 36 and 15 °C, respectively. These results indicated that Hsp70 was inducible by bacterial, osmotic, and thermal stress, and therefore plays an important role, different from antibacterial peptide, in innate immune responses of S. paramamosain.

Expression and characterization of cecropinXJ, a bioactive antimicrobial peptide from Bombyx mori (Bombycidae, Lepidoptera) in Escherichia coli

Insect antimicrobial peptides (AMPs) have a broad antimicrobial spectrum. To aid the characterization of the gene function and further applications, we cloned the gene of cecropinXJ into the prokaryotic expression vector pET32a and expressed cecropinXJ in Escherichia coli BL2l (DE3). Following induction by isopropyl-β-D-thiogalactoside (IPTG), a 25 kDa fusion peptide of cecropinXJ with a tagged thioredoxin (Trx) protein was highly expressed in E. coli. The yield was 10 mg/l culture medium following purification on nickel-nitrilotriacetic acid (Ni-NTA) metal affinity chromatography matrices. The purified recombinant antibacterial peptide, cecropinXJ, retained a high stability against Staphylococcus aureus over a temperature range from 4 to 100°C and a pH range from pH 2.0 to 12.0. The minimum inhibitory concentration (MIC) of the fusion protein against S. aureus was 0.4 μM. The recombinant cecropinXJ is also cytotoxic to several types of human cancer cells.

Expression, purification and characterization of cecropin antibacterial peptide from Bombyx mori in Saccharomyces cerevisiae

CecropinXJ is a cationic antimicrobial peptide originally isolated from the larvae of Bombyx mori. In this study, an antibacterial peptide gene of cecropinXJ was cloned into the pYES2/CT/α Factor expression vector and expressed in the Saccharomyces cerevisiae INVSc1 strain. Following an induction of recombinant protein expression in yeast for 120 h, the maximum amount of total secreted protein was 1.437 g/L. The percentage of recombinant cecropinXJ was estimated to be 79.45% of the total protein. After purification with Ni-NTA agarose column, recombinant cecropinXJ was noted to exert strong antimicrobial activities against a broad-spectrum of microorganisms, including Gram-negative and Gram-positive bacteria. Its minimal inhibitory concentration (MIC) against Escherichia coli ATCC25922 was 0.81 μM. In addition, transmission electron microscopy (TEM) analysis indicated that the surfaces of the treated pathogens underwent obvious morphological changes compared with the untreated controls, suggesting that this antimicrobial peptide exerts its action by directly disrupting membranes of microorganisms. CecropinXJ had a small hemolytic effect on red blood cells even with a peptide concentration of 200 μM. Thus, cecropinXJ acts selectively on bacterial membranes. Purified recombinant antibacterial peptide, cecropinXJ, retained a high stability against E. coli ATCC25922 over a temperature range from 4 °C to 100 °C and a pH range from pH 2.0 to 12.0. Taken together, this study demonstrates that recombinant cecropinXJ can be produced in large quantities in yeast with genetic engineering methods, and that it has strong and rapid antimicrobial activities against all of microorganisms tested. Our results suggest that cecropinXJ is a potential candidate for therapy.

Expression systems for heterologous production of antimicrobial peptides

Antimicrobial peptides (AMPs) consist of molecules that act on the defense systems of numerous organisms toward multiple pathogens such as bacteria, fungi, parasites and viruses. These compounds have become extremely significant due to the increasing resistance of microorganisms to common antibiotics. However, the low quantity of peptides obtained from direct purification is, to date, still a remarkable bottleneck for scientific and industrial research development. Therefore, this review describes the main heterologous systems currently used for AMP production, including bacteria, fungi and plants, and also the related strategies for reaching greater functional peptide production. The main difficulties of each system are also described in order to provide some directions for AMP production. In summary, data revised here indicate that large-scale production of AMPs can be obtained using biotechnological tools, and the products may be applied in the pharmaceutical industry as well as in agribusiness.

Overview on the recent study of antimicrobial peptides: origins, functions, relative mechanisms and application

Antimicrobial peptides (AMPs), which are produced by several species including insects, other animals, micro-organisms and synthesis, are a critical component of the natural defense system. With the growing problem of pathogenic organisms resistant to conventional antibiotics, especially with the emergence of NDM-1, there is increased interest in the pharmacological application of AMPs. They can protect against a broad array of infectious agents, such as bacteria, fungi, parasite, virus and cancer cells. AMPs have a very good future in the application in pharmaceuticals industry and food additive. This review focuses on the AMPs from different origins in these recent years, and discusses their various functions and relative mechanisms of action. It will provide some detailed files for clinical research of pharmaceuticals industry and food additive in application.

cDNA cloning and characterization of the antibacterial peptide cecropin 1 from the diamondback moth, Plutella xylostella L

Cecropins are linear cationic antibacterial peptides that have potent activities against microorganisms. In the present study, a 480bp full-length cDNA encoding diamondback moth (Plutella xylostella) cecropin 1 (designated as Px-cec1) was obtained using RT-PCR. A Northern blot analysis showed that the Px-cec1 transcript was predominantly expressed in fat bodies, hemocytes, midgut and epidermis with the highest expression level in fat bodies. The expression of Px-cec1 mRNA in fat bodies was significantly increased 24h after microbial challenge, with the highest induced expression by Staphylococcus aureus. A circular dichroism (CD) analysis revealed that the recombinant Px-cec1 mainly contained α-helixes. Antimicrobial assays demonstrated that recombinant Px-cec1 exhibited a broad spectrum of anti-microbial properties against fungi, Gram-positive and Gram-negative bacteria, but it did not exhibit hemolytic activity against human erythrocytes. Furthermore, Px-cec1 caused significant morphological alterations of S. aureus, as shown by scanning electron microscopy and transmission electron microscopy. These results demonstrated that Px-cec1 exerts its antibacterial activity by acting on the cell membrane to disrupt bacterial cell structures.

Production, purification, and characterization of the cecropin from Plutella xylostella, pxCECA1, using an intein-induced self-cleavable system in Escherichia coli

Antimicrobial peptides (AMPs) are widely expressed and play an important role in innate immune defense against infectious agents such as bacteria, viruses, fungi, and parasites. Cecropins are a family of AMPs synthesized in the fat body of insects that have proven effective at killing specific pathogens. In order to fulfill their clinical potential as antimicrobial drugs, a simple, cost-effective method to express AMPs is sorely needed. In this study, we expressed and characterized the cecropin from Plutella xylostella (pxCECA1) using an intein-dependent expression system in Escherichia coli. We cloned the pxCECA1 gene from larva by RT-PCR and fused the encoding sequence of mature pxCECA1 with an intein gene and a chitin-binding domain gene (CBD) in pTWIN1 plasmid. The fusion protein CBD-intein-pxCECA1 was expressed in E. coli BL21 (DE3) and separated by flowing cell extracts through a chitin column. Subsequently, self-cleavage of the intein at its C-terminus was induced in a temperature- and pH-dependent manner, resulting in the release of mature pxCECA1. The optimal conditions for self-cleavage were determined to be pH 6.0 for 48 h at 4°C, under which 12.3 mg of recombinant pxCECA1 could be recovered from 1 l of E. coli culture. The purified pxCECA1 displayed antimicrobial activity against a broad variety of gram-positive and gram-negative bacteria. This preparation was especially effective against Staphylococcus aureus, including methicillin-resistant strains. Catalase release assays demonstrated that pxCECA1 acts as a microbicidal agent. These results show for the first time that the IMPACT-TWIN expression system is an efficient, cost-effective way to produce fully functional AMPs and that the AMP pxCECA1 is a novel microbicidal agent with promising therapeutic applications.

Control of apple blue mold by Pichia pastoris recombinant strains expressing cecropin A

Recombinant Pichia pastoris yeasts expressing cecropin A (GS115/CEC), was evaluated for the control of the blue mold of apple caused by Penicillium expansum due to cecropin A peptide's effective antimicrobial effects on P. expansum spores by the thiazolyl blue (MTT) assay. Then, the protein concentration was determined and it was expressed at high levels up to 14.2 mg/L in the culture medium. Meanwhile, the population growth was assayed in vivo. The population growth of recombinant strain GS115/CEC was higher than that of non-transformed strain GS115 in red Fuji apples wounds. Recombinant yeast strains GS115/CEC significantly inhibited growth of germinated P. expansum spores in vitro and inhibited decay development caused by P. expansum in apple fruits in vivo when compared with apple fruits inoculated with sterile water or the yeast strain GS115/pPIC (plasmid pPIC9k transformed in GS115). This study demonstrated the potential of expression of the antifungal peptide in yeast for the control of postharvest blue mold infections on pome fruits.

High efficiency preparation of bioactive human alpha-defensin 6 in Escherichia coli Origami(DE3)pLysS by soluble fusion expression

Human alpha-defensin 6 (HD(6)), a small cysteine-rich cationic peptide specially expressed in epithelial cells of digestive tract, may play a crucial role in mucosal immunity. This is the first report on efficient production of bioactive HD(6) through a gene-engineering approach in Escherichia coli. The recombinant plasmid pET32a-omHD(6) was primarily constructed by inserting a PCR fragment encoding mature HD(6) peptide (mHD(6)) preceded by an enterokinase recognition sequence into the expression vector pET32a(+), in frame with the upstream thioredoxin (TrxA) gene. Under optimized expression conditions, a high percentage (>60%) of soluble TrxA-omHD(6) fusion protein was obtained with a yield of about 1.69 g/l, and the theoretical productivity of recombinant mHD(6) (rmHD(6)) reached 0.38 g/l. A feasible three-step purification strategy involving nickel-sepharose chromatography, enterokinase-cleavage and cation exchange chromatography was developed to purify rmHD(6), followed by characteristic identifications by Western blot, mass spectrometry and sequencing. About 102 mg/l of rmHD(6) with its intact N-terminal amino acid sequence was finally achieved. The in vitro experiments showed that rmHD(6) possesses high potency to inhibit herpes simplex virus-2 infection. This work settles substantial foundation for further functional study of HD(6).

A novel approach to the antimicrobial activity of maggot debridement therapy

Objectives

Commercially produced sterile green bottle fly Lucilia sericata maggots are successfully employed by practitioners worldwide to clean a multitude of chronic necrotic wounds and reduce wound bacterial burdens during maggot debridement therapy (MDT). Secretions from the maggots exhibit antimicrobial activity along with other activities beneficial for wound healing. With the rise of multidrug-resistant bacteria, new approaches to identifying the active compounds responsible for the antimicrobial activity within this treatment are imperative. Therefore, the aim of this study was to use a novel approach to investigate the output of secreted proteins from the maggots under conditions mimicking clinical treatments.

Methods

cDNA libraries constructed from microdissected salivary glands and whole maggots, respectively, were treated with transposon-assisted signal trapping (TAST), a technique selecting for the identification of secreted proteins. Several putative secreted components of insect immunity were identified, including a defensin named lucifensin, which was produced recombinantly as a Trx-fusion protein in Escherichia coli, purified using immobilized metal affinity chromatography and reverse-phase HPLC, and tested in vitro against Gram-positive and Gram-negative bacterial strains.

Results

Lucifensin was active against Staphylococcus carnosus, Streptococcus pyogenes and Streptococcus pneumoniae (MIC 2 mg/L), as well as Staphylococcus aureus (MIC 16 mg/L). The peptide did not show antimicrobial activity towards Gram-negative bacteria. The MIC of lucifensin for the methicillin-resistant S. aureus and glycopeptide-intermediate S. aureus isolates tested ranged from 8 to >128 mg/L.

Conclusions

The TAST results did not reveal any highly secreted compounds with putative antimicrobial activity, implying an alternative antimicrobial activity of MDT. Lucifensin showed antimicrobial activities comparable to other defensins and could have potential as a future drug candidate scaffold, for redesign for other applications besides the topical treatment of infected wounds.

Expression of the antimicrobial peptide cecropin fused with human lysozyme in Escherichia coli

Lysozyme is an abundant, cationic antimicrobial protein that plays an important role in host defense. It targets the beta (1-4) glycosidic bond between N-acetylglucosamine and N-acetylmuramic residues that make up peptidoglycan, making lysozyme highly active against Gram-positive bacteria. However, lysozyme alone is inactive against Gram-negative bacteria because it cannot reach the peptidoglycan layer. Cecropins are cationic molecules with a wide range of antimicrobial activities. The main target for these peptides is the cytoplasmic membrane. We resume that cecopin may disrupt the outer membrane, giving the enzyme access to the peptidoglycan in cell wall. So in the present study, novel hybrid protein combining Musca domestica cecropin (Mdc) with human lysozyme (Hly) was designed. The DNA sequence encoding recombination fusion protein Mdc-hly was cloned into the pET-32a vector for protein expression in Escherichia coli strain BL21 (DE3). The protein was expressed as a His-tagged fusion protein, and the Mdc-hly was released from the fusion by enterokinase cleavage and separated from the carrier thioredoxin. Antimicrobial activity assays showed that the recombinant fusion protein Mdc-hly has improved in vitro antimicrobial activity and action spectrum compared to Mdc and hly. Mdc-hly may have important potential application as a future safely administered human drug and food additive.