Expression and purification of the antimicrobial peptide GSL1 in bacteria for raising antibodies

Glycine-replaced epinecidin-1 variant bestows better stability and stronger antimicrobial activity against a range of nosocomial pathogenic bacteria

Epinecidin-1 (epi-1), an antimicrobial peptide first identified in marine grouper fish, has multifunctional bioactivities. The present study aims to improve its therapeutic potential via structural modifications that could enhance its antimicrobial activity and stability. To achieve it, we replaced glycine and the first histidine in the parent epi-1 with lysine, which resulted in a peptide with a repeating KXXK motif and improved physiochemical properties related to antimicrobial activity. This modified peptide, referred to as glycine-to-lysine replaced-epi-1, also gained stability and a twofold increase in helical propensity. To produce the active peptide, overlap extension PCR was employed to generate the gene of GK-epi-1 via site-directed mutagenesis, which was then cloned into the pET-32a vector and expressed as a recombinant fusion protein in Escherichia coli C43 (DE3) strain. The recombinant protein was purified and digested with enterokinase to release the active peptide fragment, which was then evaluated for antimicrobial activity and stability. The lysine substitution led to an enhancement in broad-spectrum antimicrobial activity against a wide range of nosocomial pathogenic bacteria.

Heterologous Production of Antimicrobial Peptides: Notes to Consider

Heavy and irresponsible use of antibiotics in the last century has put selection pressure on the microbes to evolve even faster and develop more resilient strains. In the confrontation with such sometimes called "superbugs", the search for new sources of biochemical antibiotics seems to have reached the limit. In the last two decades, bioactive antimicrobial peptides (AMPs), which are polypeptide chains with less than 100 amino acids, have attracted the attention of many in the control of microbial pathogens, more than the other types of antibiotics. AMPs are groups of components involved in the immune response of many living organisms, and have come to light as new frontiers in fighting with microbes. AMPs are generally produced in minute amounts within organisms; therefore, to address the market, they have to be either produced on a large scale through recombinant DNA technology or to be synthesized via chemical methods. Here, heterologous expression of AMPs within bacterial, fungal, yeast, plants, and insect cells, and points that need to be considered towards their industrialization will be reviewed.

Improving Photocleavage Efficiency of Photocleavable Protein for Antimicrobial Peptide Histatin 1 Expression

BACKGROUND

Antimicrobial peptides (AMPs) are promising alternative agents for antibiotics to overcome antibiotic resistance problems. But, it is difficult to produce large-scale antimicrobial research due to the toxicity towards expression hosts or degradation by peptidases in the host. Therefore, heterologous recombinant expression of antimicrobial peptides has always been a challenging issue.

OBJECTIVES

To overcome toxicity to the expression host and low expression level, a new photocleavable protein fusion expression method for antimicrobial peptides is provided.3 Methods: Through directed evolution and high throughput screening, a photocleavable protein mutant R6-2-6-4 with a higher photocleavage efficiency was obtained. The DNA coding sequence of antimicrobial peptide Histatin 1 was fused within the sequence of R6-2-6-4 gene. The fusion gene was successfully expressed in Escherichia coli expression system.

RESULTS

Antimicrobial peptide Histatin 1 could be successfully expressed and purified by fusing within PhoCl mutant R6-2-6-4. The antimicrobial activity was rarely affected, and the MIC value was 33 ug/mL, which was basically equivalent to 32 ug/mL of the chemically synthesized Histatin 1. After amplification in a 5 L fermenter, the expression of PhoCl mutant (R6-2-6-4)-Histatin1 improved up to 87.6 mg/L in fermenter, and Histatin1 obtained by photocleavage also could up to 11 mg/L. The prepared Histatin1 powder remained stable when stored at 4oC for up to 4 months without any degradation. In addition, the expression and photocleavage of β -Defensin105 and Lysostaphin verified the certain universality of the PhoCl mutant fusion expression system.

CONCLUSION

Antimicrobial peptides Histatin 1, β -Defensin 105 and Lysostaphin were successfully expressed and purified by photocleavable protein mutant. This may provide a novel strategy to express and purify antimicrobial peptides in the Escherichia coli expression system.

Andrographolide and 4-Phenylbutyric Acid Administration Increase the Expression of Antimicrobial Peptides Beta-Defensin-1 and Cathelicidin and Reduce Mortality in Murine Sepsis

Antibiotic resistance is a global threat and requires the search for new treatment strategies. Natural antimicrobial peptides (AMPs) have pronounced antibacterial, antiviral, antifungal, and antitumor activity. AMPs’ clinical use is complicated by the high synthesis costs and rapid proteolytic degradation. The search for small molecules, inducers of endogenous AMP expression, could become a new approach. Here, we investigated for the first time the effect of seven small molecules (andrographolide, levofloxacin, azithromycin, montelukast, 4-phenylbutyric acid, rosuvastatin and valsartan) on AMP (beta-defensin-1, hBD-1 and cathelicidin, LL-37) serum levels in rats. In control groups, the level of hBD-1 was 295.0 (292.9–315.4) pg/mL, and for LL-37, it was 223.8 (213.3–233.6) pg/mL. Andrographolide (ANDR) and 4-phenylbutyric acid (4-PHBA) administration significantly enhanced the level of both AMPs. The hBD-1 level was 581.5 (476.3–607.7) pg/mL for ANDR and 436.9 (399.0–531.6) pg/mL for 4-PHBA. The LL-37 level was 415.4 (376.2–453.8) pg/mL for ANDR and 398.9 (355.7–410.1) pg/mL for 4-PHBA. Moreover, we have shown that these compounds reduce mortality in a murine model of sepsis caused by a carbapenem-resistant Klebsiella aerogenes isolate. From our point of view, these small molecules are promising candidates for further study as potent AMP inducers. The data obtained allow the development of new strategies to combat antibiotic resistance and infectious diseases.

Immunological detection of AcAMP antimicrobial peptide secreted by Aspergillus clavatus

Background and Objectives:

Aspergillus clavatus antimicrobial peptide (AcAMP) is a fungi-derived peptide with a broad spectrum of activity against pathogenic bacteria and fungi. Natural antimicrobial peptides, including AcAMP, have attracted many attentions in the development of new natural antibiotics against pathogenic bacteria, especially multidrug resistant ones.

Materials and Methods:

In the present study, acamp gene was codon-optimized and chemically synthesized in pUC57 cloning vector, subcloned into pET28a (+) expression vector and transferred into competent Escherichia coli BL21 (DE3) cells. The expression of AcAMP was induced by addition of Isopropyl β- d-1-thiogalactopyranoside (IPTG) and the expressed peptide was purified by Ni-NTA. BALB/c mice were immunized with the purified peptide and the ability of the immunized mice sera for the detection of the native AcAMP secreted by A. clavatus IRAN 142C was examined through ELISA and Western blotting techniques.

Results:

Both ELISA and Western blotting demonstrated the ability of the sera of the immunized mice to detect the native AcAMP.

Conclusion:

The results of the present work show that the raised antibody against recombinant AcAMP can be used to detect AcAMP peptide, an issue which paves the way to develop detection kits for the detection of AcAMP-producing organisms, purification of this valuable peptide for further investigations.

In Vivo Bactericidal Efficacy of GWH1 Antimicrobial Peptide Displayed on Protein Nanoparticles, a Potential Alternative to Antibiotics

Oligomerization of antimicrobial peptides into nanosized supramolecular complexes produced in biological systems (inclusion bodies and self-assembling nanoparticles) seems an appealing alternative to conventional antibiotics. In this work, the antimicrobial peptide, GWH1, was N-terminally fused to two different scaffold proteins, namely, GFP and IFN-γ for its bacterial production in the form of such recombinant protein complexes. Protein self-assembling as regular soluble protein nanoparticles was achieved in the case of GWH1-GFP, while oligomerization into bacterial inclusion bodies was reached in both constructions. Among all these types of therapeutic proteins, protein nanoparticles of GWH1-GFP showed the highest bactericidal effect in an in vitro assay against Escherichia coli, whereas non-oligomerized GWH1-GFP and GWH1-IFN-γ only displayed a moderate bactericidal activity. These results indicate that the biological activity of GWH1 is specifically enhanced in the form of regular multi-display configurations. Those in vitro observations were fully validated against a bacterial infection using a mouse mastitis model, in which the GWH1-GFP soluble nanoparticles were able to effectively reduce bacterial loads.

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.

Potato Snakin-1: an antimicrobial player of the trade-off between host defense and development

Snakin-1 (SN1) from potato is a cysteine-rich antimicrobial peptide with high evolutionary conservation. It has 63 amino acid residues, 12 of which are cysteines capable of forming six disulfide bonds. SN1 localizes in the plasma membrane, and it is present mainly in tissues associated with active growth and cell division. SN1 is active in vitro against bacteria, fungus, yeasts, and even animal/human pathogens. It was demonstrated that it also confers in vivo protection against commercially relevant pathogens in overexpressing potato, wheat, and lettuce plants. Although researchers have demonstrated SN1 can disrupt the membranes of E. coli, its integral antimicrobial mechanism remains unknown. It is likely that broad-spectrum antimicrobial activity is a combined outcome of membrane disruption and inhibition of intracellular functions. Besides, in potato, partial SN1 silencing affects cell division, leaf metabolism, and cell wall composition, thus revealing additional roles in growth and development. Its silencing also affects reactive oxygen species (ROS) and ROS scavenger levels. This finding indicates its participation in redox balance. Moreover, SN1 alters hormone levels, suggesting its involvement in the complex hormonal crosstalk. Altogether, SN1 has the potential to integrate development and defense signals directly and/or indirectly by modulating protein activity, modifying hormone balance and/or participating in redox regulation. Evidence supports a paramount role to SN1 in the mechanism underlying growth and immunity balance. Furthermore, SN1 may be a promising candidate in preservation, and pharmaceutical or agricultural biotechnology applications.

Antimicrobial Peptides: Recent Insights on Biotechnological Interventions and Future Perspectives

With the unprecedented rise of drug-resistant pathogens, particularly antibiotic-resistant bacteria, and no new antibiotics in the pipeline over the last three decades, the issue of antimicrobial resistance has emerged as a critical public health threat. Antimicrobial Peptides (AMP) have garnered interest as a viable solution to this grave issue and are being explored for their potential antimicrobial applications. Given their low bioavailability in nature, tailoring new AMPs or strategizing approaches for increasing the yield of AMPs, therefore, becomes pertinent. The present review focuses on biotechnological interventions directed towards enhanced AMP synthesis and revisits existing genetic engineering and synthetic biology strategies for production of AMPs. This review further underscores the importance and potential applications of advanced gene editing technologies for the synthesis of novel AMPs in future.

Expression in Escherichia coli of novel recombinant hybrid antimicrobial peptide AL32-P113 with enhanced antimicrobial activity in vitro

Antibiotic-resistant pathogens have become a major public health problem worldwide. New discoveries and strategies as regards antibiotic drug development are urgently in need for curing infected patients. Antimicrobial peptides (AMPs) are short cationic peptides that play important roles in innate immune system with a broad spectrum of antimicrobial activity. Recently, hybrid AMPs have been reported to increase antimicrobial activity, stability, and in vivo half-life. In the present study, a gene encoding for AL32-P113 hybrid peptide consisting of two truncated active forms of human LL-37 and histatin-5 (Hst-5) was commercially constructed, cloned into pTXB-1 commercial plasmid, and expressed in E. coli BL21 (DE3). To increase the yield of target protein expression, IPTG concentration, time and temperature were optimized. The results indicate that AL32-P113-intein fusion protein with 33.7 kDa was expressed mostly in inclusion form and estimated to be 20% of the total protein. After chitin affinity purification, 5.7-kDa of AL32-P113 peptide was separated with an average concentration of 12.1 mg per litre of bacterial culture and over 86% purity. The minimum inhibitory concentration (MIC) was evaluated for antimicrobial activity determination of recombinant AL32-P113 compared to synthetic peptides, LL-37, Hst-5, and L31-P113. The results implied that both hybrid peptides exhibited potent antimicrobial activity against gram-negative bacteria and yeast cells whereas the L31-P113 peptide possessed approximately four times greater antimicrobial activity in gram-positive bacteria than parent LL-37. An increasing of undesired hemolysis of these hybrid peptides toward human red cells was also observed when red blood cell hemolytic assay was performed. Several factors including charge and secondary structure predicted by public software were utilized for explanation of the antimicrobial potency of both hybrid peptides. This study proved that hybrid peptides show broader and more potent antimicrobial ability against pathogens and they could be applied as a therapeutic approach for topical treatment of microbial infection in the future.

Successful production of the potato antimicrobial peptide Snakin-1 in baculovirus-infected insect cells and development of specific antibodies

Background

Snakin-1 (StSN1) is a broad-spectrum antimicrobial cysteine-rich peptide isolated from Solanum tuberosum. Its biotechnological potential has been already recognized since it exhibits in vivo antifungal and antibacterial activity. Most attempts to produce StSN1, or homologous peptides, in a soluble native state using bacterial, yeast or synthetic expression systems have presented production bottlenecks such as insolubility, misfolding or low yields.

Results

In this work, we successfully expressed a recombinant StSN1 (rSN1) in Spodoptera frugiperda (Sf9) insect cells by optimizing several of the parameters for its expression in the baculovirus expression system. The recombinant peptide lacking its putative signal peptide was soluble and was present in the nuclear fraction of infected Sf9 cells. An optimized purification procedure allowed the production of rSN1 that was used for immunization of mice, which gave rise to polyclonal antibodies that detect the native protein in tissue extracts of both agroinfiltrated plants and stable transgenic lines. Our results demonstrated that this system circumvents all the difficulties associated with recombinant antimicrobial peptides expression in other heterologous systems.

Conclusions

The present study is the first report of a successful protocol to produce a soluble Snakin/GASA peptide in baculovirus-infected insect cells. Our work demonstrates that the nuclear localization of rSN1 in insect cells can be exploited for its large-scale production and subsequent generation of specific anti-rSN1 antibodies. We suggest the use of the baculovirus system for high-level expression of Snakin/GASA peptides, for biological assays, structural and functional analysis and antibody production, as an important step to both elucidate their accurate physiological role and to deepen the study of their biotechnological uses.

Electronic supplementary material

The online version of this article (10.1186/s12896-017-0401-2) contains supplementary material, which is available to authorized users.

A high-throughput expression screening platform to optimize the production of antimicrobial peptides

Background

Antimicrobial peptides (AMPs) are promising candidates for the development of novel antibiotics, but it is difficult to produce sufficient quantities for preclinical and clinical studies due to their toxicity towards microbial expression hosts. To avoid laborious trial-and-error testing for the identification of suitable expression constructs, we have developed a small-scale expression screening platform based on a combinatorial plasmid library.

Results

The combinatorial library is based on the Golden Gate cloning system. In each reaction, six donor plasmids (each containing one component: a promoter, fusion partner 1, fusion partner 2, protease cleavage site, gene of interest, or transcriptional terminator) were combined with one acceptor plasmid to yield the final expression construct. As a proof of concept, screening was carried out in Escherichia coli and Pichia pastoris to study the expression of three different model AMPs with challenging characteristics, such as host toxicity or multiple disulfide bonds. The corresponding genes were successfully cloned in 27 E. coli and 18 P. pastoris expression plasmids, each in a one-step Golden Gate reaction. After transformation, small-scale expression screening in microtiter plates was followed by AMP quantification using a His₆ tag-specific ELISA. Depending on the plasmid features and the expression host, the protein yields differed by more than an order of magnitude. This allowed the identification of high producers suitable for larger-scale protein expression.

Conclusions

The optimization of recombinant protein production is best achieved from first principles by initially optimizing the genetic construct. The unrestricted combination of multiple plasmid features yields a comprehensive library of expression strains that can be screened for optimal productivity. The availability of such a platform could benefit all laboratories working in the field of recombinant protein expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0637-5) contains supplementary material, which is available to authorized users.

Screening, Expression, Purification and Functional Characterization of Novel Antimicrobial Peptide Genes from Hermetia illucens (L.)

Antimicrobial peptides from a wide spectrum of insects possess potent microbicidal properties against microbial-related diseases. In this study, seven new gene fragments of three types of antimicrobial peptides were obtained from Hermetia illucens (L), and were named cecropinZ1, sarcotoxin1, sarcotoxin (2a), sarcotoxin (2b), sarcotoxin3, stomoxynZH1, and stomoxynZH1(a). Among these genes, a 189-basepair gene (stomoxynZH1) was cloned into the pET32a expression vector and expressed in the Escherichia coli as a fusion protein with thioredoxin. Results show that Trx-stomoxynZH1 exhibits diverse inhibitory activity on various pathogens, including Gram-positive bacterium Staphylococcus aureus, Gram-negative bacterium Escherichia coli, fungus Rhizoctonia solani Khün (rice)-10, and fungus Sclerotinia sclerotiorum (Lib.) de Bary-14. The minimum inhibitory concentration of Trx-stomoxynZH1 is higher against Gram-positive bacteria than against Gram-negative bacteria but similar between the fungal strains. These results indicate that H. illucens (L.) could provide a rich source for the discovery of novel antimicrobial peptides. Importantly, stomoxynZH1 displays a potential benefit in controlling antibiotic-resistant pathogens.