Expression and purification of two different antimicrobial peptides, PR-39 and Protegrin-1 in Escherichia coli

Carrier proteins boost expression of PR-39-derived peptide in Pichia pastoris

AIMS

Multidrug resistance presents difficulties in preventing and treating bacterial infections. Proline-rich antimicrobial peptides (PrAMPs) inhibit bacterial growth by affecting the intracellular targets rather than by permeabilizing the membrane. The aim of this study was to develop a yeast-based fusion carrier system using calmodulin (CaM) and xylanase (XynCDBFV) as two carriers to express the model PrAMP PR-39-derived peptide (PR-39-DP) in Pichia pastoris.

METHODS AND RESULTS

Fusion protein secreted into the culture supernatant was purified in a one-step on-column digestion using human rhinovirus 3C protease, obtaining the target peptide PR-39-DP. The growth curves of Escherichia coli were monitored by recording the OD600 values of the bacteria. The antibacterial activity of PR-39-DP was evaluated in killing assays performed on E. coli. The yield of PR-39-DP was 1.0-1.2 mg l-1 in the CaM fusion carrier system, approximately three times that of the XynCDBFV fusion carrier system. The minimal inhibitory concentration of PR-39-DP was ∼10.5 µg ml-1.

CONCLUSIONS

CaM and XynCDBFV provide increased stability and promote the expression and secretion of active PR-39-DP.

Biodegradable Polymers and Polymer Composites with Antibacterial Properties

Antibiotic resistance is one of the greatest threats to global health and food security today. It becomes increasingly difficult to treat infectious disorders because antibiotics, even the newest ones, are becoming less and less effective. One of the ways taken in the Global Plan of Action announced at the World Health Assembly in May 2015 is to ensure the prevention and treatment of infectious diseases. In order to do so, attempts are made to develop new antimicrobial therapeutics, including biomaterials with antibacterial activity, such as polycationic polymers, polypeptides, and polymeric systems, to provide non-antibiotic therapeutic agents, such as selected biologically active nanoparticles and chemical compounds. Another key issue is preventing food from contamination by developing antibacterial packaging materials, particularly based on degradable polymers and biocomposites. This review, in a cross-sectional way, describes the most significant research activities conducted in recent years in the field of the development of polymeric materials and polymer composites with antibacterial properties. We particularly focus on natural polymers, i.e., polysaccharides and polypeptides, which present a mechanism for combating many highly pathogenic microorganisms. We also attempt to use this knowledge to obtain synthetic polymers with similar antibacterial activity.

Antimicrobial Peptides in Gut Health: A Review

Animal antimicrobial peptides (AMPs), known as broad-spectrum and high-efficiency antibacterial activity, are important effector molecules in innate immune system. AMPs not only have antimicrobial, antiviral and antitumor effects but also exhibit important effects in vivo, such as anti-inflammatory response, recruiting immune cells, promoting epithelial damage repair, and promoting phagocytosis of bacteria. However, research on the application of AMPs is incomplete and controversial. This review mainly introduces the classification of AMPs, biological functions, as well as the mechanisms of action, expression rules, and nutrition regulation from three perspectives, aiming to provide important information for the application of AMPs.

Heterologous production of porcine derived antimicrobial peptide PR-39 in Escherichia coli using SUMO and intein fusion systems

About half a century after antibiotics discovery, multi-antibiotic-resistant bacteria posed a new challenge to medicine. Attempts to discover new antibiotics have drawn the attention to Antimicrobial Peptides (AMPs). The rapid growth, besides its known genetic and manipulation systems, makes E. coli the preferred host system for production of recombinant proteins on an industrial scale. To produce AMPs in E. coli, the application of fusion-tags with the aim of stability, solubility, and prevention of antimicrobial activity is one of the best practices in this regard. In this study, we presented two different expression systems for the production of PR-39 in E. coli; one in fusion with intein-Chitin binding domain (CBD) and another in fusion with SUMO accompanied by polyhistidine affinity tag. Both were cloned in the NdeI-XhoI sites of pET-17b and transformed to E. coli BL21 (DE3) pLysS. Recombinant bacteria were cultured and induced with 0.4 mM IPTG at 30 °C. Expression and purification of target proteins were confirmed by Tricine- SDS-PAGE and dot blot analysis. Recovery of 250 μg PR-39/L from SUMO fusion system and 280 μg PR-39/L from the intein fusion system was achieved. Both purified peptides showed antibacterial activity using MIC/MBC demonstrating their functionality after SUMO and intein mediated purification.

The Binary Effect on Methicillin-Resistant Staphylococcus aureus of Polymeric Nanovesicles Appended by Proline-Rich Amino Acid Sequences and Inorganic Nanoparticles

Prevalent research underscores efforts to engineer highly sophisticated nanovesicles that are functionalized to combat antibiotic-resistant bacterial infections, especially those caused by methicillin-resistant Staphylococcus aureus (MRSA), and that aid with wound healing or immunomodulation. This is especially relevant for patients who are susceptible to Staphylococcus aureus infections postoperatively. Here, antibacterial formulations are incorporated into polymeric, biocompatible vesicles called polymersomes (PsNPs) that self-assemble via hydrophobic interactions of admixed aqueous and organic substances. Nano-PsNPs are synthesized using a high molecular weight amphiphilic block copolymer, and are conjugated to include antimicrobial peptides (AMPs) along the peripheral hydrophilic region and silver nanoparticles (AgNPs) inside their hydrophobic corona. In vitro testing on bacterial and human cell lines indicates that finely tuned treatment concentrations of AMP and AgNPs in PsNPs synergistically inhibits the growth of MRSA without posing significant side effects, as compared with other potent treatment strategies. A ratio of silver-to-AMP of about 1:5.8 corresponding to ≈11.6 µg mL^-1 of silver nanoparticles and 14.3 × 10^-6 m of the peptide, yields complete MRSA inhibition over a 23 h time frame. This bacteriostatic activity, coupled with nominal cytotoxicity toward native human dermal fibroblast cells, extends the potential for AMP/AgNP polymersome therapies to replace antibiotics in the clinical setting.

Secretion of the recombination α-amylase in Escherichia coli and purification by the gram-positive enhancer matrix (GEM) particles

α-Amylases are important enzymes in industry. A recombinant α-amylase with a secretion signal peptide and an AcmA tag was expressed in Escherichia coli to improve the yield. The induction concentrations were optimized, and the temperature had a significant influence on soluble expression and secretion. A visible band could be obtained when the induction was conducted at 16 °C. The gram-positive enhancer matrix (GEM) particles could separate and purify the recombinant α-amylase with the AcmA tag, and no visible band could be seen in the culture even after the culture was concentrated ten times. The solution and concentration of the recombinant α-amylase could be adjusted by GEM particles. The recombinant untagged α-amylase was obtained after digestion. The α-amylase was characterized. The recombinant α-amylase was a thermophilic enzyme with a broad pH tolerance. In addition, the enzyme activity of the recombinant α-amylase was independent of Ca²⁺. The recombinant α-amylase contained the OmpA signal peptide and the AcmA tag and was expressed and purified quickly and easily.

Constitutive expression of antimicrobial peptide PR-39 in transgenic mice significantly enhances resistance to bacterial infection and promotes growth

Use of huge amounts of antibiotics in farm animal production has promoted the prevalence of antibiotic-resistant bacteria, which poses a serious threat to public health. Therefore, alternative approaches are needed to reduce or replace antibiotic usage in the food animal industry. PR-39 is a pig-derived proline-rich antimicrobial peptide that has a broad spectrum of antibacterial activity and a low propensity for development of resistance by microorganisms. To test whether ubiquitous expression of PR-39 in transgenic (TG) mice can increase resistance against bacterial infection, we generated TG mice that ubiquitously express a pig-derived antimicrobial peptide PR-39 and analyzed their growth and resistance to infection of the highly pathogenic Actinobacillus pleuropneumoniae (APP) isolated from swine. The growth performance was significantly increased in TG mice compared with their wild-type (WT) littermates. After the APP challenge, TG mice exhibited a significantly higher survival rate and significantly lower tissue bacterial load than WT littermates. Furthermore, the tissue lesion severity that resulted from APP infection was milder in TG mice than that in their WT littermates. This study provides a good foundation for the development of PR-39-expressing TG animals, which could reduce the use of antibiotics in the farm animal industry.

Do antimicrobial peptides PR-39, PMAP-36 and PMAP-37 have any effect on bacterial growth and quality of liquid-stored boar semen?

The use of antimicrobial peptides (AMP) has become one of the most promising alternatives to the use of antibiotics (Abs) in semen extender's formulation to overcome the increasing bacterial resistance to antibiotics. However, AMP may impair boar sperm quality, so that their deleterious effects might be higher than their effectiveness against bacteria. Thus, the aim of this study was to determine whether three different AMP, the proline-arginine-rich antimicrobial peptide PR-39 (PR-39), and the porcine myeloid antimicrobial peptides 36 (PMAP-36) and 37 (PMAP-37) had any effect upon boar sperm quality and bacterial growth. For this purpose, three different concentrations of each peptide (1 μM, 10 μM and 20 μM for PR-39 and 0.5 μM, 1 μM and 3 μM for PMAP-36 and PMAP-37) were added to 2 mL of a pool of extended semen with BTS without Abs; two controls, one without AMPs and Abs, and the other with Abs only were used for each peptide (n = 3). Total (TMOT) and progressive (PMOT) sperm motility, sperm viability and bacterial concentration were assessed before the addition of each AMP or Abs and at 1, 3, 6, 8 and 10 days post-addition. For each AMP, results revealed a drop in the TMOT and PMOT in all treatments and controls. In regard to sperm viability, while PR-39 at 10 μM maintained it in values similar to those of the control with Abs and PMAP-36 kept also the sperm viability in a similar fashion to the treatment with Abs, PMAP-37 was more effective in keeping sperm viability than controls (P < 0.05). Whereas PR-39 at 20 μM and PMAP-37 at 3 μM were quite effective in controlling bacterial load, PMAP-36 did not avoid bacterial growth at any concentration tested. In conclusion, taking all results together, PMAP-37 seems to be a suitable candidate to replace Abs in extended semen, as it hardly impairs sperm viability and controls the bacterial load. Nevertheless, further studies are still required to improve its effectiveness.

Probiotic Lactobacillus casei expressing porcine antimicrobial peptide PR39 elevates antibacterial activity in the gastrointestinal tract

PR39, a 4.7 kDa proline-rich antimicrobial peptide, acts as a cationic host defense peptide. In addition to killing bacteria, PR39 mediates inflammatory reactions, including cell proliferation, migration, wound healing, and angiogenesis. Here, we examined the antibacterial effects of this peptide. The synthetic gene fragment PR39 was inserted into the secretory expression vector plasmid pPG:612 of Lactobacillus casei, yielding the recombinant strain pPG:612-PR39/L. casei 393. In vitro antibacterial tests showed that expression of the PR39 peptide in recombinant L. casei resulted in antibacterial activity against Escherichia coli and Salmonella but had only minor antibacterial effects in Staphylococcus aureus. In addition, BALB/c mice fed the recombinant pPG:612-PR39/L. casei 393 grew better and had increased peripheral blood lymphocyte percentages, white blood cell numbers, and spleen indices than mice in the control group. Scanning electron microscopy showed that jejunum and duodenum villus height, crypt depth, and the ratio of villus height/crypt depth in the intestinal villi also increased. Moreover, mice fed the recombinant strain showed significantly lower mortality rates than the control group mice when challenged with the enterotoxigenic E. coli K88⁺. Thus, this recombinant expression system had the beneficial characteristics of both L. casei and PR39, supporting its potential as an animal feed additive.

Green fluorescent protein as a scaffold for high efficiency production of functional bacteriotoxic proteins in Escherichia coli

The availability of simple, robust, and cost-effective methods for the large-scale production of bacteriotoxic peptides such as antimicrobial peptides (AMPs) is essential for basic and pharmaceutical research. However, the production of bacteriotoxic proteins has been difficult due to a high degree of toxicity in bacteria and proteolytic degradation. In this study, we inserted AMPs into the Green fluorescent protein (GFP) in a loop region and expressed them as insoluble proteins in high yield, circumventing the inherent toxicity of AMP production in Escherichia coli. The AMPs inserted were released by cyanogen bromide and purified by chromatography. We showed that highly potent AMPs such as Protegrin-1, PMAP-36, Buforin-2, and Bactridin-1 are produced in high yields and produced AMPs showed similar activities compared to chemically synthesized AMPs. We increased the yield more than two-fold by inserting three copies of Protegrin-1 in the GFP scaffold. The immunogold electron micrographs showed that the expressed Protegrin-1 in the GFP scaffold forms large and small size aggregates in the core region of the inclusion body and become entirely nonfunctional, therefore not influencing the proliferation of E. coli. Our novel method will be applicable for diverse bacteriotoxic peptides which can be exploited in biomedical and pharmaceutical researches.

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

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

Expression of porcine protegrin-1 in Pichia pastoris and its anticancer activity in vitro

Protegrin-1 (PG-1), a β-hairpin antimicrobial peptide (AMP), is amongst the shortest AMPs in sequence length while remaining active against a variety of microorganisms. The aim of this study was produce recombinant PG-1 and investigate its anticancer activity. A DNA sequence encoding the mature PG-1, fused with a 6His-tag, was cloned into the pPICZα-A vector and transformed into Pichia pastoris. Expression was induced following culture for ~96 h with 1% methanol at 28°C, and ~15.6 mg PG-1 was expressed in 100 ml culture medium. Following purification using a Ni-chelating Sepharose column, ~20 mg pure active PG-1 was obtained from 500 ml culture broth supernatant. The expressed PG-1/6His exhibited strong dose- and time-dependent anticancer activity against HepG2 cells in vitro.

Antimicrobial and immunomodulatory activities of PR-39 derived peptides

The porcine cathelicidin PR-39 is a host defence peptide that plays a pivotal role in the innate immune defence of the pig against infections. Besides direct antimicrobial activity, it is involved in immunomodulation, wound healing and several other biological processes. In this study, the antimicrobial- and immunomodulatory activity of PR-39, and N- and C-terminal derivatives of PR-39 were tested. PR-39 exhibited an unexpected broad antimicrobial spectrum including several Gram positive strains such as Bacillus globigii and Enterococcus faecalis. Of organisms tested, only Staphylococcus aureus was insensitive to PR-39. Truncation of PR-39 down to 15 (N-terminal) amino acids did not lead to major loss of activity, while peptides corresponding to the C-terminal part of PR-39 were hampered in their antimicrobial activity. However, shorter peptides were all much more sensitive to inhibition by salt. Active peptides induced ATP leakage and loss of membrane potential in Bacillus globigii and Escherichia coli, indicating a lytic mechanism of action for these peptides. Finally, only the mature peptide was able to induce IL-8 production in porcine macrophages, but some shorter peptides also had an effect on TNF-α production showing differential regulation of cytokine induction by PR-39 derived peptides. None of the active peptides showed high cytotoxicity highlighting the potential of these peptides for use as an alternative to antibiotics.

Recombinant expression of novel protegrin-1 dimer and LL-37-linker-histatin-5 hybrid peptide mediated biotin carboxyl carrier protein fusion partner

Antimicrobial peptides (AMPs) hold great promise as potential therapeutic approach for curing of infectious diseases. Prokaryotic protein expression renders high scalability with an effective purification of several heterogeneous proteins. However, it might be inappropriate for recombinant AMPs expression thereby its antimicrobial activity against the host cells. Several fusion partners demonstrated antimicrobial activity neutralization of AMPs expression and purification in Escherichia coli. In order to improve the antimicrobial effect, several hybrid AMPs have been designed and developed. As expected to increase the antimicrobial activity, a dimeric form of porcine protegrin-1 (PG-1) and human LL-37-linker-histatin-5 (LL-37-linker-Hst-5) hybrid peptide were alternatively constructed in this study. Hydroxylamine hydrochloride and thrombin cleavage sites were designed for releasing of hybrid peptide and PG-1 dimer from biotin carboxyl carrier protein (BCCP) fusion partner. The full-length AMPs gene was connected down-stream of BCCP gene using the overlap extension-PCR, cloned into pET-28a vector and expressed in E. coli BL21(DE3)pLysS. After IPTG induction, approximately 20% of BCCP-AMPs was expressed as intracytoplasmic inclusion bodies with an expected molecular weight of 24.5kDa. The mean of purified and refolded BCCP-AMPs was 1.5mg/L with 76% purity. The presence of expressed protein was subsequently determined by Western blotting analysis. Finally, radial diffusion assay supported that these peptides displayed functional antimicrobial activity against E. coli and Staphylococcus aureus standard strains. Two novel AMPs established in this study would be potentially developed as extensive intervention for treating of infectious diseases.

Real-time SPR characterization of the interactions between multi-epitope proteins and antibodies against classical swine fever virus

The envelope glycoprotein E2 is the major immunodominant protein of the classical swine fever virus and can induce neutralizing antibodies and protective host-immune responses in infected swine. We designed, expressed, and purified multi-epitope protein (GST-BT22) that contains a tandem repeat of the E2 antigenic-determinant residues 693-704, 770-780, and 826-843, each of which is separated by a GGSSGG sequence. In the same manner, we also designed, expressed, and purified a second protein (GST-BT23) that contains a C-terminal sequence consisting of residues 1446-1460 from the classical swine fever virus nonstructural protein NS2-3 separated from the GST-BT22 sequence by a GGSSGG sequence. Western blotting of GST-BT22 and GST-BT23 with serum from a swine that had been experimentally infected with the virus showed that the proteins reacted with anti-serum, whereas GST did not. Surface plasmon resonance was used to quantify the affinities of GST-BT22 and GST-BT23 for serum antibodies (K(a) = 4.31 × 10(8) and 5.01 × 10(8), respectively). GST, used as a control, was reacted an order of magnitude less strongly than did GST-BT22 and GST-BT23. Surface plasmon resonance, therefore, appears to be a sensitive and precise method for epitope evaluation and can be used to characterize the immunogenicity of a recombinant protein.

Real-time analysis of the interaction of a multiple-epitope peptide with antibodies against classical swine fever virus using surface plasmon resonance

The E2 envelope glycoprotein is the major immunodominant protein of classical swine fever virus (CSFV), and can induce neutralizing antibodies and protective immune responses in infected swine. We developed a tandem-repeat multiple-epitope recombinant protein that contains two copies of each of the regions of E2 spanned by residues 693-704, 770-780, and 826-843, coupled by two copies of the region spanned by residues 1446-1460 of the CSFV nonstructural protein NS2-3. The chemically synthesized gene was expressed in Escherichia coli as a fusion with glutathione S-8 (GST), named GST-BT21. After it was purified with Glutathione Sepharose 4B, we used Western blotting to characterize the construct and surface plasmon resonance to analyze its affinity and specific interaction with CSFV-positive serum. Purified GST-BT21 protein displayed excellent immunoreactivity with antiserum against CSFV (Tian et al., 2012), and surface plasmon resonance confirmed the specific affinity between BT21, but not GST, and antibodies in serum from animals infected with CSFV. Surface plasmon resonance is a sensitive and precise method for epitope evaluation, and it can be used to characterize the immunogenicity and functions of recombinant proteins.

Expression and purification of the antimicrobial peptide cecropin AD by fusion with cationic elastin-like polypeptides

Cationic elastin-like polypeptides (CELP) are thermally responsive polypeptides that undergo an inverse temperature phase transition, and the recombinant CELP fusion proteins may be purified by inverse transition cycling (ITC). To obtain high-purity antimicrobial peptide cecropin AD (CAD), CELP was placed at the N-terminus of CAD and the expression vector pET28a-CELP-CAD was constructed. The expression vector was then transformed into Escherichia coli BL21 (DE3) to express the recombinant protein. After three rounds of ITC, enterokinase digestion and another hot spin, 1.2mg recombinant CAD was purified from 100ml culture medium. The antimicrobial test indicated that the high-purity CAD had strong antimicrobial activity against E. coli and Staphylococcus aureus.

Expression and purification of 15N- and 13C-isotope labeled 40-residue human Alzheimer's β-amyloid peptide for NMR-based structural analysis

Amyloid fibrils of Alzheimer's β-amyloid peptide (Aβ) are a primary component of amyloid plaques, a hallmark of Alzheimer's disease (AD). Enormous attention has been given to the structural features and functions of Aβ in amyloid fibrils and other type of aggregates in associated with development of AD. This report describes an efficient protocol to express and purify high-quality 40-residue Aβ(1-40), the most abundant Aβ in brains, for structural studies by NMR spectroscopy. Over-expression of Aβ(1-40) with glutathione S-transferase (GST) tag connected by a Factor Xa recognition site (IEGR(▾)) in Escherichia coli resulted in the formation of insoluble inclusion bodies even with the soluble GST tag. This problem was resolved by efficient recovery of the GST-Aβ fusion protein from the inclusion bodies using 0.5% (w/v) sodium lauroyl sarcosinate as solubilizing agent and subsequent purification by affinity chromatography using a glutathione agarose column. The removal of the GST tag by Factor Xa enzymatic cleavage and purification by HPLC yielded as much as ∼7 mg and ∼1.5mg of unlabeled Aβ(1-40) and uniformly (15)N- and/or (13)C-protein Aβ(1-40) from 1L of the cell culture, respectively. Mass spectroscopy of unlabeled and labeled Aβ and (1)H/(15)N HSQC solution NMR spectrum of the obtained (15)N-labeled Aβ in the monomeric form confirmed the expression of native Aβ(1-40). It was also confirmed by electron micrography and solid-state NMR analysis that the purified Aβ(1-40) self-assembles into β-sheet rich amyloid fibrils. To the best of our knowledge, our protocol offers the highest yields among published protocols for production of recombinant Aβ(1-40) samples that are amendable for an NMR-based structural analysis. The protocol may be applied to efficient preparation of other amyloid-forming proteins and peptides that are (13)C- and (15)N-labeled for NMR experiments.