Expressing antimicrobial peptide cathelicidin-BF in Bacillus subtilis using SUMO technology

Microbial production systems and optimization strategies of antimicrobial peptides: a review

Antibiotic resistance has become a public safety issue of the twenty-first century, posing a growing threat and drawing increased attention. Compared to traditional antibiotics, antimicrobial peptides (AMPs), as naturally produced small peptides, can target multiple pathways within pathogens and render them less prone to developing resistance. This makes them promising alternatives to antibiotics. However, traditional chemical synthesis methods face challenges, such as high costs, low yields, and poor stability, limiting the large-scale industrial production of AMPs. Despite extensive research to improve AMP production efficiency, issues such as low yields and complex extraction processes continue to pose significant barriers to commercial application. Therefore, there is an urgent need for new biosynthesis strategies and optimization methods to enhance AMP production efficiency and quality. This review summarizes the sources, classification, mechanisms of action and recent advances in the microbial synthesis of AMPs. It also explores innovative production methods, including recombinant microbial expression systems, fusion tags, codon optimization, tandem multimer expression, and hybrid peptide expression. Furthermore, we review the applications of gene editing technologies and artificial intelligence in AMP production, providing new perspectives and strategies for efficient, large-scale AMP production.

Detection and optimization of microbial expression systems for extracellular production and purification of Ca2+-responsive phase-changing annexin fusions

Previously, we identified the human annexin A1 as a purification tag for column-free purification with gentler calcium-responsive precipitation. In this work, we used the annexin A1 tagged green fluorescent protein constructs for detecting extracellular production in Escherichia coli, Bacillus subtilis, and Pichia pastoris, and identified that the leaderless fusion protein was transported extracellularly in E. coli with supply of additives including Triton X-100. The coexpressed enzymes, culture compositions, and induction conditions in E. coli extracellular expression systems were optimized. With coexpression of phospholipase C from Bacillus cereus and addition of 0.2 % Triton X-100 after induction for 60 h at 28 °C, the annexin A1 tagged green fluorescent protein and 5-aminolevulinate dehydratase from E. coli were overexpressed and purified from lysogeny broth by precipitation with 20 mM Ca2+ and redissolution with 25 mM EDTA with the acceptable protein purities and recoveries. The silica binding peptide was fused to the annexin A1 tagged fluorescent protein fusion for successive affinity precipitation and purification. With incubation of the specific protease, the released tag-free protein displayed higher purity via on-resin cleavage than that through cleavage of the free fusion protein. The tandem tag is applicable for two-step purification of small or large amounts of other fusion proteins in the culture and recovery of tag-free proteins at low cost.

Extracellular production of antifungal peptides from oxidative endotoxin-free E. coli and application

Antifungal peptides (AFPs) can be used as novel preservatives, but achieving large-scale production and application remains a long-term challenge. In this study, we developed a hybrid peptide MD (metchnikowin-drosomycin fusion) secreted into Escherichia coli supernatant, demonstrating strong inhibitory activity against Aspergillus flavus and Botrytis cinerea. The fusion tag did not impact its activity. Moreover, an endotoxin-free and oxidative leaky strain was developed by knocking out the trxB, gor, and lpp genes of endotoxin-free E. coli ClearColi-BL21(DE3). This strain facilitates the proper folding of multi-disulfide bond proteins and promotes the extracellular production of recombinant bioactive AFP MD, achieving efficient production of endotoxin-free MD. In addition, temperature control replaces chemical inducers to further reduce production costs and circumvent the toxicity of inducers. This extracellularly produced MD exhibited favorable effectiveness in inhibiting fruit mold growth, and its safety was preliminarily established by gavage testing in mice, suggesting that it can be developed into a green and sustainable fruit fungicide. In conclusion, this study provides novel approaches and systematic concepts for producing extracellularly active proteins or peptides with industrial significance. KEY POINTS: • First report of extracellular production of bioactive antifungal peptide in Escherichia coli. • The hybrid antifungal peptide MD showed strong inhibitory activity against Aspergillus flavus and Botrytis cinerea, and the activity was not affected by the fusion tag. • Endotoxin-free oxidative Escherichia coli suitable for the expression of multi-disulfide bond proteins was constructed.

Soluble Expression of Antimicrobial Peptide BSN-37 from Escherichia coli by SUMO Fusion Technology

Antimicrobial peptides (AMPs) are a kind of small molecular peptide that an organism produces to resist the invasion of foreign microorganisms. AMP BSN-37 is a bovine AMP that exhibits high antibacterial activity. In this paper, the optimized gene AMP BSN-37 was cloned into pCold-SUMO for fusion expression by recombinant DNA technology. The gene sequence of AMP BSN-37 was obtained by codons reverse translation, and the codons were optimized according to the codons preference of Escherichia coli (E. coli). The recombinant plasmid was constructed and identified by PCR, enzyme digestion and sequencing. Then the recombinant plasmid was transformed into BL21 E. coli to induce expression, and the IPTG concentration and time were optimized. The expressed soluble fusion protein SUMO-BSN-37 was purified by chromatography and then cleaved by SUMO proteases to release BSN-37. SDS-PAGE electrophoresis and Western blotting were used for identification. The recombinant plasmid pCold-SUMO-BSN-37 was obtained, and the fusion AMP BSN-37 was preliminarily expressed in BL21. After optimization, the optimal expression condition was 37 ℃ with 0.4 µM IPTG and 6 h incubation. Under optimal conditions, a large amount of fusion AMP BSN-37 was obtained by purification. Western blotting showed that the fusion peptide was successfully expressed and had good activity. The expressed BSN-37 showed antimicrobial activity similar to that of synthesized BSN-37. In this study, soluble expression products of AMP BSN-37 were obtained, and the problem regarding the limited source of AMP BSN-37 could be effectively solved, laying a foundation for further research on AMP BSN-37.

High expression of antimicrobial peptides cathelicidin-BF in Pichia pastoris and verification of its activity

Antibacterial peptides are endogenous polypeptides produced by multicellular organisms to protect the host against pathogenic microbes, they show broad spectrum antimicrobial activities against various microorganisms and possess low propensity for developing resistance. The purpose of this study is to develop recombinant antibacterial peptide cathelicidin-BF by genetic engineering and protein engineering technology, and study its antibacterial activity in vitro and in vivo, so as to provide reference for the production and application of recombinant antibacterial peptide cathelicidin-BF. In this study, on account of Pichia pastoris eukaryotic expression system, we expressed and prepared antibacterial peptide cathelicidin-BF. Then, the minimum inhibitory concentration of antibacterial peptide cathelicidin-BF and the comparison with the antibacterial activity of antibiotics were determined through the antibacterial experiment in vitro. Chickens as infection model were used to verify the antibacterial peptide activity in vivo. The results show that the bacteriostatic ability of antibacterial peptide cathelicidin-BF is similar to that of antibiotics in certain concentration, and can reach the treatment level of antibiotics. Although the mode of administration of antibacterial peptide is still limited, this study can provide reference for the future research of antibacterial peptide.

The future of recombinant host defense peptides

The antimicrobial resistance crisis calls for the discovery and production of new antimicrobials. Host defense peptides (HDPs) are small proteins with potent antibacterial and immunomodulatory activities that are attractive for translational applications, with several already under clinical trials. Traditionally, antimicrobial peptides have been produced by chemical synthesis, which is expensive and requires the use of toxic reagents, hindering the large-scale development of HDPs. Alternatively, HDPs can be produced recombinantly to overcome these limitations. Their antimicrobial nature, however, can make them toxic to the hosts of recombinant production. In this review we explore the different strategies that are used to fine-tune their activities, bioengineer them, and optimize the recombinant production of HDPs in various cell factories.

Heparan sulfate proteoglycans-mediated targeted delivery of TGF-β1-binding peptide to liver for improved anti-liver fibrotic activity in vitro and in vivo

Elevated expressions of transforming growth factor β1 (TGF-β1) have been implicated in the pathogenesis of liver fibrosis, thus attenuating the excessive TGF-β1's activity by TGF-β1-binding peptide is an ideal strategy for the treatment of liver fibrosis. However, the application of small peptide as a pharmaceutical agent is obstacle due to difficult preparation and non-selective delivery. The I-plus sequences of circumsporozoite protein (CSP-I) possesses high affinity for heparan sulfate proteoglycans, which are primarily located on liver tissues. TGF-β1-binding peptide P15 holds specific ability of binding to TGF-β1. In this study, we describe an approach to efficiently preparing liver-targeting peptide P15-CSP-I, which is conjugation of the sequences of P15 to the N-terminus of CSP-I, from the cleavage of biological macromolecule SUMO-tagged P15-CSP-I. In vitro and ex vivo binding assay showed that P15-CSP-I specifically targeted to the hepatocytes and liver tissues. Moreover, P15-CSP-I inhibited cell proliferation, migration and invasion, and decreased fibrosis-related proteins expression in TGF-β1-activated HSCs in vitro. Furthermore, P15-CSP-I ameliorated liver morphology and decreased the fibrosis responses in vivo. Taken together, P15-CSP-I may be a potential candidate for targeting therapy on liver fibrosis due to its high efficient preparation, specific liver-targeting potential and improved anti-liver fibrotic activity.

Expression and characterization of hemagglutinin-neuraminidase protein from Newcastle disease virus in Bacillus subtilis WB800

Background

Newcastle disease virus (NDV) belongs to the genus Avaluvirus and Paramyxoviridae family, and it can cause acute, highly contagious Newcastle disease in poultry. The two proteins, haemagglutinin neuraminidase (HN) and Fusion (F), are the main virulence factor of the virus and play an essential role in immunogenicity against the virus. In most paramyxoviruses, the F protein requires HN protein to fuse the membrane, and HN proteins substantially enhance the viruses’ fusion activity.

Results

The present study describes the successful cloning and expression of HN protein from NDV in Bacillus subtilis WB800 using the modified shuttle vector pHT43. HN coding sequence was cloned into the pGet II vector. It was then subcloned into the PHT43 shuttle vector and transferred to Escherichia coli for replication. The recombinant plasmid was extracted from E. coli and used to transform B. subtilis by electroporation. After induction of recombinant B. subtilis by IPTG, total cell protein and the protein secreted into the media were analysed through a time course using SDS-PAGE. The expressed HN protein was purified using cation exchange chromatography followed by metal affinity chromatography, using the 6× His epitope introduced at the carboxyl terminus of the recombinant protein. The accuracy of the PHT43-HN construct was confirmed by sequencing and enzymatic digestion. SDS-PAGE results showed that the recombinant HN protein was successfully expressed and secreted into the medium. Moreover, the purified HN protein showed neuraminidase activity with characteristics similar to the indigenous HN NDV protein. B. subtilis is a free endotoxin host that could be a favourite prokaryotic platform for producing the recombinant HN protein.

Conclusion

The establishment of this expression and purification system has allowed us to explore further the biochemical characteristics of HN protein and obtain material that could be suitable for a new production of NDV candidate vaccine with high immunogenicity.

CBP22, a Novel Bacteriocin Isolated from Clostridium butyricum ZJU-F1, Protects against LPS-Induced Intestinal Injury through Maintaining the Tight Junction Complex

A novel bacteriocin secreted by Clostridium butyricum ZJU-F1 was isolated using ammonium sulfate fractionation, cation exchange chromatography, affinity chromatography, and reverse-phase high-performance liquid chromatography (RP-HPLC). The bacteriocin, named CBP22, contained 22 amino acids with the sequence PSAWQITKCAGSIAWALGSGIF. Analysis of its structure and physicochemical properties indicated that CBP22 had a molecular weight of 2264.63 Da and a +1 net charge. CBP22 showed activity against E. col K88, E. coli ATCC25922, and S. aureus ATCC26923. The effects and potential mechanisms of bacteriocin CBP22 on the innate immune response were investigated with a lipopolysaccharide- (LPS-) induced mouse model. The results showed that pretreatment with CBP22 prevented LPS-induced impairment in epithelial tissues and significantly reduced serum levels of IgG, IgA, IgM, TNF-α, and sIgA. Moreover, CBP22 treatment increased the expression of the zonula occludens and reduced permeability as well as apoptosis in the jejunum in LPS-treated mice. In summary, CBP22 inhibits the intestinal injury and prevents the gut barrier dysfunction induced by LPS, suggesting the potential use of CBP22 for treating intestinal damage.

Production of proteins and commodity chemicals using engineered Bacillus subtilis platform strain

Currently, increasing demand of biochemicals produced from renewable resources has motivated researchers to seek microbial production strategies instead of traditional chemical methods. As a microbial platform, Bacillus subtilis possesses many advantages including the generally recognized safe status, clear metabolic networks, short growth cycle, mature genetic editing methods and efficient protein secretion systems. Engineered B. subtilis strains are being increasingly used in laboratory research and in industry for the production of valuable proteins and other chemicals. In this review, we first describe the recent advances of bioinformatics strategies during the research and applications of B. subtilis. Secondly, the applications of B. subtilis in enzymes and recombinant proteins production are summarized. Further, the recent progress in employing metabolic engineering and synthetic biology strategies in B. subtilis platform strain to produce commodity chemicals is systematically introduced and compared. Finally, the major limitations for the further development of B. subtilis platform strain and possible future directions for its research are also discussed.

Design, Dimerization, and Recombinant Production of MCh-AMP1-Derived Peptide in Escherichia coli and Evaluation of Its Antifungal Activity and Cytotoxicity

Fungal species resistant to current antifungal agents are considered as a serious threat to human health, the dilemma that has dragged attentions toward other sources of antifungals such as antimicrobial peptides (AMPs). In order to improve biological activity of a recently described antifungal peptide MCh-AMP1 from Matricaria chamomilla flowers, MCh-AMP1dimer (DiMCh-AMP1), containing 61 amino acid residues connected by flexible linker (GPDGSGPDESGPDES), was designed and expressed in Escherichia coli, and its structure was analyzed using bioinformatics tools. DiMCh-AMP1 synthetic gene was cloned into pET-28a expression vector, which was then used to transform E. coli BL21 (DE3) strain. His-tag purification was achieved using metal-chelate affinity chromatography. Because there is no methionine residue in the DiMCh-AMP1 sequence, cyanogen bromide was successfully used to separate the target product from the tag. Reverse-phase high-performance liquid chromatography was used as the final step of purification. Results showed that recombinant peptide was produced in considerable amounts (0.9 mg/L) with improved antifungal activity toward both yeasts and molds compared to its monomeric counterpart. The minimum inhibition concentration and minimum fungicidal concentration values of DiMCh-AMP1 against Candida and Aspergillus species were reported in the range of 1.67-6.66 μM and 3.33-26.64 μM, respectively. Our results showed that while antifungal activity of dimerized peptide was improved considerably, its cytotoxicity was decreased, implying that DiMCh-AMP1 could be a potential candidate to design an effective antifungal agent against pathogenic yeasts and molds.

Antimicrobial and Amyloidogenic Activity of Peptides. Can Antimicrobial Peptides Be Used against SARS-CoV-2?

At present, much attention is paid to the use of antimicrobial peptides (AMPs) of natural and artificial origin to combat pathogens. AMPs have several points that determine their biological activity. We analyzed the structural properties of AMPs, as well as described their mechanism of action and impact on pathogenic bacteria and viruses. Recently published data on the development of new AMP drugs based on a combination of molecular design and genetic engineering approaches are presented. In this article, we have focused on information on the amyloidogenic properties of AMP. This review examines AMP development strategies from the perspective of the current high prevalence of antibiotic-resistant bacteria, and the potential prospects and challenges of using AMPs against infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Cathelicidin-BF attenuate kidney injury through inhibiting oxidative stress, inflammation and fibrosis in streptozotocin-induced diabetic rats

OBJECTIVE

To investigate protective efficacies and mechanisms of Cathelicidin-BF (BF-30) peptide on streptozotocin (STZ)-induced diabetic kidney injury.

METHODS

Effects of BF-30 on hydrogen peroxide induced oxidative damage in HK-2 renal cells were assessed by CCK-8 method. Forty STZ-induced diabetic rats with kidney injury were randomly divided into model control group, BF-30 group at different doses (0.1, 0.3 and 0.9 mg/kg). Blood biochemical and kidney related indexes as well adrenal morphological changes, inflammation related markers of diabetic rats were measured.

RESULTS

Cell viability of HK-2 cells with oxidative damage induced by hydrogen peroxide were significantly improved by BF-30 with 0.8 μg/mL for 56.5% and 1.6 μg/mL for 82.3% compared with control. Moreover, the decreased reactive oxygen species (ROS), and increased intracellular antioxidant enzymes GPX1, SOD2 and GSH were showed in BF-30 treated groups. In addition, co-incubation of BF-30 in HK-2 cells promoted the increase of p-AMPK and LC3, decreased activation of p-mTOR, BAX and Caspase 3. Chronic treatment of BF-30 improved the STZ-induced diabetic characteristics of diabetic kidney disease (DKD) model rats. Further renal histopathological examination revealed 12-week treatment of BF-30 effectively improved the morphology of nephropathy in DKD rats. Moreover, BF-30 also could ameliorate excessive oxidative stress, renal cell apoptosis and fibrosis, thereby protects renal tissues.

CONCLUSION

BF-30 exerted protective effects on STZ-induced kidney injury mainly through the inhibiting oxidative stress in kidney tissue, reducing renal fibrosis, increasing autophagy, and reducing the renal cell apoptosis related proteins to decrease the cell damage and protect nephrocytes.

Recombinant expression, purification and PEGylation of Paneth cell peptide (cryptdin-2) with value added attributes against Staphylococcus aureus

Cryptdins are disulfide-rich cationic antimicrobial peptides secreted by mouse Paneth cells and are known to exhibit potent antimicrobial activity against various deadly pathogens. Keeping in view the extremely low yield obtained from mouse Paneth cells and high cost of synthetic peptide(s), herein, we have attempted to produce cryptdin-2 in Escherichia coli using recombinant technology. To avoid lethal effects of peptide on the host cells, cryptdin-2 was expressed as a fusion protein with thioredoxin as fusion partner which yielded 40 mg/L protein in the soluble fraction. Subsequently, mature cryptdin-2 was cleaved from the fusion partner and purified by cation exchange chromatography. Since conjugation of poly(ethylene) glycol (PEG) has been known to improve the biological properties of biomolecules, therefore, we further attempted to prepare PEG-conjugated variant of cryptdin-2 using thiol specific PEGylation. Though the antimicrobial activity of PEGylated cryptdin-2 was compromised to some extent, but it was found to have enhanced serum stability for longer duration as compared to its un-modified forms. Also, it was found to exhibit reduced toxicity to the host cells. Further, its synergism with gentamicin suggests that PEGylated cryptdin-2 can be used with conventional antibiotics, thereby indicating its possibility to be used as an adjunct therapy.

Heterologous expression of the novel α-helical hybrid peptide PR-FO in Bacillus subtilis

PR-FO is a novel α-helical hybrid antimicrobial peptide (AMP) with strong antimicrobial activities and high stability, and the potential to develop into a new generation of antimicrobial agents. In this study, the encoded gene sequence of SMT3-PR-FO was designed and transformed into B. subtilis WB800N. Fusion proteins with concentrations of 16 mg L^-1 (SP_amyQ) and 23 mg L^-1 (SP_sacB) were obtained after purification by a Ni-NTA resin column. A total of 3 mg (SP_amyQ) and 4 mg (SP_sacB) of PR-FO with a purity of 90% was obtained from 1 L fermentation cultures. Recombinant PR-FO exhibited high inhibition activities against both gram-negative bacteria and gram-positive bacteria, and low haemolytic activity against human red blood cells. These results indicated that the rSMT3-PR-FO could be expressed under the guidance of SP_amyQ and SP_sacB, and the maltose-induced expression strategy might be a safe and efficient method for the soluble peptides production in B. subtilis.

Hitchhiking with Nature: Snake Venom Peptides to Fight Cancer and Superbugs

Abstract

For decades, natural products in general and snake venoms (SV) in particular have been a rich source of bioactive compounds for drug discovery, and they remain a promising substrate for therapeutic development. Currently, a handful of SV-based drugs for diagnosis and treatment of various cardiovascular disorders and blood abnormalities are on the market. Likewise, far more SV compounds and their mimetics are under investigation today for diverse therapeutic applications, including antibiotic-resistant bacteria and cancer. In this review, we analyze the state of the art regarding SV-derived compounds with therapeutic potential, focusing on the development of antimicrobial and anticancer drugs. Specifically, information about SV peptides experimentally validated or predicted to act as antimicrobial and anticancer peptides (AMPs and ACPs, respectively) has been collected and analyzed. Their principal activities both in vitro and in vivo, structures, mechanisms of action, and attempts at sequence optimization are discussed in order to highlight their potential as drug leads.

Key Contribution

This review describes the state of the art in snake venom-derived peptides and their therapeutic applications. This work reinforces the potential of snake venom components as therapeutic agents, particularly in the quest for new antimicrobial and anticancer drugs.

Antifungal Peptides as Therapeutic Agents

Fungi have been used since ancient times in food and beverage-making processes and, more recently, have been harnessed for the production of antibiotics and in processes of relevance to the bioeconomy. Moreover, they are starting to gain attention as a key component of the human microbiome. However, fungi are also responsible for human infections. The incidence of community-acquired and nosocomial fungal infections has increased considerably in recent decades. Antibiotic resistance development, the increasing number of immunodeficiency- and/or immunosuppression-related diseases and limited therapeutic options available are triggering the search for novel alternatives. These new antifungals should be less toxic for the host, with targeted or broader antimicrobial spectra (for diseases of known and unknown etiology, respectively) and modes of actions that limit the potential for the emergence of resistance among pathogenic fungi. Given these criteria, antimicrobial peptides with antifungal properties, i.e., antifungal peptides (AFPs), have emerged as powerful candidates due to their efficacy and high selectivity. In this review, we provide an overview of the bioactivity and classification of AFPs (natural and synthetic) as well as their mode of action and advantages over current antifungal drugs. Additionally, natural, heterologous and synthetic production of AFPs with a view to greater levels of exploitation is discussed. Finally, we evaluate the current and potential applications of these peptides, along with the future challenges relating to antifungal treatments.

Advanced Strategies for Food-Grade Protein Production: A New E. coli/Lactic Acid Bacteria Shuttle Vector for Improved Cloning and Food-Grade Expression

Food-grade production of recombinant proteins in Gram-positive bacteria, especially in LAB (i.e., Lactococcus, Lactobacillus, and Streptococcus), is of great interest in the areas of recombinant enzyme production, industrial food fermentation, gene and metabolic engineering, as well as antigen delivery for oral vaccination. Food-grade expression relies on hosts generally considered as safe organisms and on clone selection not dependent on antibiotic markers, which limit the overall DNA manipulation workflow, as it can be carried out only in the expression host and not in E. coli. Moreover, many commercial expression vectors lack useful elements for protein purification. We constructed a “shuttle” vector containing a removable selective marker, which allows feasible cloning steps in E. coli and subsequent protein expression in LAB. In fact, the cassette can be easily excised from the selected recombinant plasmid, and the resulting marker-free vector transformed into the final LAB host. Further useful elements, as improved MCS, 6xHis-Tag, and thrombin cleavage site sequences were introduced. The resulting vector allows easy cloning in E. coli, can be quickly converted in a food-grade expression vector and harbors additional elements for improved recombinant protein purification. Overall, such features make the new vector an improved tool for food-grade expression.

The YoaW signal peptide directs efficient secretion of different heterologous proteins fused to a StrepII-SUMO tag in Bacillus subtilis

Background

Heterologous gene expression is well established for various prokaryotic model systems. However, low yield, incorrect folding and instability still impede the production of soluble, bioactive proteins. To improve protein production with the Gram-positive host Bacillus subtilis, a secretory expression system was designed that enhances translocation, folding and stability of heterologous proteins, and simplifies purification. Based on the theta-replication plasmid pHT01, a B. subtilis secretory expression vector was constructed that encodes a fusion protein consisting of a signal peptide and a StrepII-tag linked to a SUMO-tag serving as a folding catalyst. The gene of a protein of interest can be translationally fused to the SUMO cassette and an additional 6xHis-tag encoding region. In order to maximize secretory expression of the construct by fitting the signal peptide to the StrepII-SUMO part of the fusion protein, a B. subtilis signal-peptide library was screened with the Escherichia coli alkaline phosphatase PhoA as a reporter.

Results

The YoaW signal peptide-encoding region (SPyoaW) was identified with highest secretory expression capacity in context with the StrepII-SUMO-tag fusion in a B. subtilis eightfold extracellular protease deletion strain. PhoA activity and fusion protein production was elevated by a factor of approximately five when compared to an α-amylase (AmyQ) signal peptide construct. Replacement of PhoA with a single-chain variable fragment antibody specific for GFP or the B. amyloliquefaciens RNase barnase, respectively, resulted in a similar enhancement of secretory expression, demonstrating universality of the YoaW signal peptide-StrepII-SUMO encoding cassette for secretory expression in B. subtilis. Optimisation of codon usage and culture conditions further increased GFP-specific scFv fusion-protein production, and a simple affinity purification strategy from culture supernatant with removal of the StrepII-SUMO-tag by SenP-processing yielded 4 mg of pure, soluble and active GFP-specific scFv from 1 l of culture under standard laboratory conditions.

Conclusions

The new expression system employing a YoaW signal peptide-StrepII-SUMO fusion will simplify secretory protein production and purification with B. subtilis. It can obviate the need for time consuming individual signal-peptide fitting to maximize yield for many different heterologous proteins of interest.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1078-0) contains supplementary material, which is available to authorized users.

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.

A Recombinant Snake Cathelicidin Derivative Peptide: Antibiofilm Properties and Expression in Escherichia coli

The emergence of antimicrobial resistance among pathogenic microorganisms has been led to an urgent need for antibiotic alternatives. Antimicrobial peptides (AMPs) have been introduced as promising therapeutic agents because of their remarkable potentials. A new modified cathelicidin-BF peptide (Cath-A) with 34 amino acid sequences, represents the potential antimicrobial effects against methicillin-resistant Staphylococcus aureus (MRSA) with slight hemolytic and cytotoxic activities on eukaryotic cells. In this study, the effects of Cath-A on Acinetobacter baumannii, and Pseudomonas aeruginosa isolated from medical instruments were studied. Cath-A inhibited the growth of bacterial cells in the range of 8⁻16 μg/mL and 16-≥256 μg/mL for A. baumannii and P. aeruginosa, respectively. The peptide significantly removed the established biofilms. To display a representative approach for the cost-effective constructions of peptides, the recombinant Cath-A was cloned in the expression vector pET-32a(+) and transformed to Escherichia coli BL21. The peptide was expressed with a thioredoxin (Trx) sequence in optimum conditions. The recombinant peptide was purified with a Ni2+ affinity chromatography and the mature peptide was released after removing the Trx fusion protein with enterokinase. The final concentration of the partially purified peptide was 17.6 mg/L of a bacterial culture which exhibited antimicrobial activities. The current expression and purification method displayed a fast and effective system to finally produce active Cath-A for further in-vitro study usage.

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.

Design, Recombinant Fusion Expression and Biological Evaluation of Vasoactive Intestinal Peptide Analogue as Novel Antimicrobial Agent

Antimicrobial peptides represent an emerging category of therapeutic agents with remarkable structural and functional diversity. Modified vasoactive intestinal peptide (VIP) (VIP analogue 8 with amino acid sequence “FTANYTRLRRQLAVRRYLAAILGRR”) without haemolytic activity and cytotoxicity displayed enhanced antimicrobial activities against Staphylococcus aureus (S. aureus) ATCC 25923 and Escherichia coli (E. coli) ATCC 25922 than parent VIP even in the presence of 180 mM NaCl or 50 mM MgCl₂, or in the range of pH 4–10. VIP analogue 8 was expressed as fusion protein thioredoxin (Trx)-VIP8 in E. coli BL21(DE) at a yield of 45.67 mg/L. The minimum inhibitory concentration (MIC) of the recombinant VIP analogue 8 against S. aureus ATCC 25923 and E. coli ATCC 25922 were 2 μM. These findings suggest that VIP analogue 8 is a promising candidate for application as a new and safe antimicrobial agent.

Suppression of the toxicity of Bac7 (1-35), a bovine peptide antibiotic, and its production in E. coli

Bac7 (1-35) is an Arg- and Pro-rich peptide antibiotic, produced in bovine cells to protect them from microbial infection. It has been demonstrated to inhibit the protein synthesis in E. coli, leading to cell death. Because of its toxicity, no cost effective methods have been developed for Bac7 production in Escherichia coli for its potential clinical use. Here, we found a method to suppress Bac7 (1-35) toxicity in E. coli to establish its high expression system, in which Bac7 (1-35) was fused to the C-terminal end of protein S, a major spore-coat protein from Myxococcus xanthus, using a linker containing a Factor Xa cleavage site. The resulting His6-PrS2-Bac7 (1-35) (PrS2 is consisted of two N-terminal half domains of protein S connected in tandem) was well expressed using the Single-Protein Production (SPP) system at low temperature and subsequently purified in a single step by using a Ni column. The combination of protein S fusion and its expression in the SPP system at low temperature appeared to suppress Bac7 (1-35) toxicity. Both the purified His6-PrS2-Bac7 (1-35) and His6-PrS2-Bac7 (1-35) treated by Factor Xa were proven to be a potent inhibitor for cell-free protein synthesis.

Expression of plectasin in Bacillus subtilis using SUMO technology by a maltose-inducible vector

Plectasin, the first fungus defensin, is especially efficient against Gram-positive bacteria. To explore an effective approach for expressing plectasin in Bacillus subtilis, the sequence encoding plectasin fused with the small ubiquitin-like modifier (SUMO) gene, the 6 × His gene and the signal peptide of SacB were cloned into an E. coli-B. subtilis shuttle vector pGJ148 in which the maltose utilization operon promoter Pglv directed the expression. The fusion protein successfully secreted in culture and approximately, 41 mg of the recombinant fusion protein SUMO-plectasin was purified per liter of culture supernatant. After purification by Ni-NTA resin column and digestion by SUMO protease, 5.5 mg of plectasin with a purity of 94 % was obtained from 1 L fermentation culture. Recombinant plectasin was found inhibition activity against S. pneumoniae, S. aureus and S. epidermidis. These results indicate that the maltose-induced expression system may be a safe and efficient way for the large-scale production of soluble peptides in B. subtilis.

Cathelicidin-BF, a Novel Antimicrobial Peptide from Bungarus fasciatus, Attenuates Disease in a Dextran Sulfate Sodium Model of Colitis

Antimicrobial peptides are molecules of innate immunity. Cathelicidin-BF is the first cathelicidin peptide found in reptiles. However, the immunoregulatory and epithelial barrier protective properties of C-BF have not been reported. Inflammatory bowel diseases, including ulcerative colitis and Crohn's disease, can lead to colon cancer, the third most common malignant tumor. The objective is to develop the new found cathelicidin-BF as a therapeutic to patients of ulcerative colitis. The morphology of the colon epithelium was observed by H&E staining; apoptosis index and infiltration of inflammatory cells in colonic epithelium were measured by TUNEL and immunohistochemistry; the expression level of endogenous mCRAMP was analyzed by immunofluorescence; and phosphorylation of the transcription factors c-jun and NF-κB in colon were analyzed by Western blot. Our results showed that the morphology of the colon epithelium in the C-BF+DSS group was improved compared with the DSS group. Apoptosis and infiltration of inflammatory cells in colonic epithelium were also significantly attenuated in the C-BF+DSS group compared with the DSS group, and the expression level of endogenous mCRAMP in the DSS group was significantly higher than other groups. DSS-induced phosphorylation level of c-jun and NF-κB while C-BF effectively inhibited phosphorylation of NF-κB (p65). The barrier protective effect of C-BF was still excellent. In conclusion, C-BF effectively attenuated inflammation and improved disrupted barrier function. Notably, this is the first report to demonstrate that C-BF attenuates DSS-induced UC both through the regulation of intestinal immune and retention of barrier function, and the exact pathway was through NF-κB.

Cellular disulfide bond formation in bioactive peptides and proteins

Bioactive peptides play important roles in metabolic regulation and modulation and many are used as therapeutics. These peptides often possess disulfide bonds, which are important for their structure, function and stability. A systematic network of enzymes--a disulfide bond generating enzyme, a disulfide bond donor enzyme and a redox cofactor--that function inside the cell dictates the formation and maintenance of disulfide bonds. The main pathways that catalyze disulfide bond formation in peptides and proteins in prokaryotes and eukaryotes are remarkably similar and share several mechanistic features. This review summarizes the formation of disulfide bonds in peptides and proteins by cellular and recombinant machinery.

Expression and one-step purification of the antimicrobial peptide cathelicidin-BF using the intein system in Bacillus subtilis

The intein expression system has been widely applied in Escherichia coli to express various proteins and peptides. However, the removal of endotoxin from the recombinant proteins expressed in E. coli is very difficult and therefore complicates the purification process. In this study, we constructed an intein-based expression vector for an antimicrobial peptide (cathelicidin from Bungarus fasciatus) and expressed the intein fusion peptide in a Bacillus subtilis expression system. The fusion peptide was secreted into the culture medium, identified by Western blot and purified by affinity chromatography and intein self-cleavage in just one step. Approximately, 0.5 mg peptide was obtained from 1 litre of culture medium. The purified peptide showed antimicrobial activity. Our results indicate that the intein expression system may be a safe and efficient method to produce soluble peptides and proteins in B. subtilis.