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 Pglv. 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.

Transgenic Brassica juncea plants expressing MsrA1, a synthetic cationic antimicrobial peptide, exhibit resistance to fungal phytopathogens.

Cationic antimicrobial peptides (CAPs) have shown potential against broad spectrum of phytopathogens. Synthetic versions with desirable properties have been modeled on these natural peptides. MsrA1 is a synthetic chimera of cecropin A and melittin CAPs with antimicrobial properties. We generated transgenic Brassica juncea plants expressing the msrA1 gene aimed at conferring fungal resistance. Five independent transgenic lines were evaluated for resistance to Alternaria brassicae and Sclerotinia sclerotiorum, two of the most devastating pathogens of B. juncea crops. In vitro assays showed inhibition by MsrA1 of Alternaria hyphae growth by 44-62 %. As assessed by the number and size of lesions and time taken for complete leaf necrosis, the Alternaria infection was delayed and restricted in the transgenic plants with the protection varying from 69 to 85 % in different transgenic lines. In case of S. sclerotiorum infection, the lesions were more severe and spread profusely in untransformed control compared with transgenic plants. The sclerotia formed in the stem of untransformed control plants were significantly more in number and larger in size than those present in the transgenic plants where disease protection of 56-71.5 % was obtained. We discuss the potential of engineering broad spectrum biotic stress tolerance by transgenic expression of CAPs in crop plants.

Unexpected mucin-type O-glycosylation and host-specific N-glycosylation of human recombinant interleukin-17A expressed in a human kidney cell line.

The T helper cell-derived cytokine interleukin-17A (IL-17A) is a variably glycosylated disulfide-linked homodimer of 34-38 kDa. Its polypeptide monomer contains one canonical N-glycosylation site at Asn68, and human recombinant IL-17A was partly N-glycosylated when expressed in human kidney (HEK293) cells as a fusion protein with a melittin signal sequence and an N-terminal hexahistidine tag. Orbitrap mass analyses of the tryptic N-glycopeptide 63-69 indicated that the N-glycosylation was of the GalNAc-terminated type characteristic of cultured kidney cells. The mass spectrum of IL-17A monomer also included peaks shifted by +948 Da from the respective masses of unglycosylated and N-glycosylated polypeptides. These were caused by unpredicted partial O-glycosylation of Thr26 with the mucin-like structure -GalNAc(-NeuNAc)-Gal-NeuNAc. Identical O-glycosylation occurred in commercially sourced recombinant IL-17A also expressed in HEK293 cells but with a different N-terminal sequence. Therefore, the kidney host cell line not only imposed its characteristic pattern of N-glycosylation on recombinant IL-17A but additionally created an O-glycosylation not known to be present in the T cell-derived cytokine. Mammalian host cell lines for recombinant protein expression generally impose their characteristic patterns of N-glycosylation on the product, but this work exemplifies how a host may also unpredictably O-glycosylate a protein that is probably not normally O-glycosylated.

[Transgenic Belarussian-bred potato plants expressing genes for antimicrobial peptides of the cecropin-melittin type].

Binary vectors for Agrobacterium-mediated transformation were constructed to express the genes for antimicrobial peptides (APs) of the cectropin-melittin type under the control of the cauliflower mosaic virus 35S RNA promoter in plants. It was shown with Escherichia coli and Agrobacterium tumefaciens cells that the cassettes could be cloned in pB1121-based vectors with deletion of the 3-D-glycuronidase gene only in the orientation opposite to that of the original vector. Transgenic potato plants were obtained using the Belarussian varieties Odyssey, Vetraz, and Scarb. Their cells expressed the MsrA1 or CEMA peptides of the cecropin-melittin type. The expression was shown to confer higher resistance to bacterial (Erwinia carotovora) infection and extremely high resistance to fungal (Phytophtora infestans and Alternarla solani) infections.

[Cloning and expression of a gene encoding shortened LfcinB(1-15)-Melittin(5-12) hybrid peptide in Escherichia coli BL21(DE3)].

In order to get new antibacterial peptide, we designed a hybrid peptide LfcinB(1-15)-Melittin(5-12), composed of 1-15 amino acid residues of bovine Lactoferricin and 5-12 amino acid residues of Melittin. According to the bias of codon utilization of Escherichia coli, We synthesized the gene encoding the hybrid peptide. We inserted the gene between the sites of Nco I and Sal I of pET-32a and obtained the recombinant expression vector for heterologous expression of LfcinB(1-15)-Melittin(5-12) in Escherichia coli. We used Escherichia coli BL21(DE3) as expression host for the recombinant plasmid. After induced by isopropyl-beta-D-thiogalactoside (IPTG) under the optimized conditions, we realized the fusion protein was successfully expressed. The fusion protein was expressed in soluble form and the level was more than 35% of the total proteins. With (His)6 x Tag, the fusion protein was easily purified by His x Bind Purification Kit. After purification, we obtained 35 mg of fusion protein from 1 L of culture medium. At last, we accomplished that the peptide LfcinB(1-15)-Melittin(5-12) was released from the fusion protein cleaved by enterokinase. The recombinant LfcinB(1-15)-Melittin(5-12) showed antimicrobial activity assayed by agar diffusion test. This is the first report on the heterologous expression of the hybrid antibacterial peptide LfcinB(1-15)-Melittin(5-12) in Escherichia coli and also provides basis for next cost-effective expression of other antimicrobial peptides in genetic engineering.

In vitro- and in vivo-targeted tumor lysis by an MMP2 cleavable melittin-LAP fusion protein.

Chemotherapy is one of the main treatment options for cancer, but the effectiveness of chemotherapeutic drugs is severely limited due to their systemic toxicity. Therefore, the need for a more targeted approach in tumor treatment is obvious. A tumor-activated agent would decrease systemic toxicity as well as increase the efficacy of the treatment. It has previously been shown that the latency of pro-TGF-beta is conferred by dimerization of two latency-associated peptides (LAP) that form a protective shield, which is cleaved off upon activation by matrix metalloproteinases (MMPs). It has also been shown that the fusion of this LAP peptide with other cytokines can confer their latency. In the present study, a recombinant adenovirus with a fusion gene encoding a tumor-activated pro-cytolytic peptide was made in which the LAP domain of TGF-beta was fused with melittin, a potent cytolytic toxin, with an MMP2 cleavage site in between the two. In vitro studies show that the melittin-MMP2-LAP recombinant adenovirus can be activated by MMP2 which leads to the release of free melittin to lyse the target cells. In vivo studies show approximately a 70% decrease in B16 tumor volume in melittin-MMP2-LAP recombinant adenovirus-treated mice as compared to control mice. No significant systemic toxicity was observed in the treated mice.

Pathogen-induced expression of a cecropin A-melittin antimicrobial peptide gene confers antifungal resistance in transgenic tobacco.

Expression of defensive genes from a promoter that is specifically activated in response to pathogen invasion is highly desirable for engineering disease-resistant plants. A plant transformation vector was constructed with transcriptional fusion between the pathogen-responsive win3.12T promoter from poplar and the gene encoding the novel cecropin A-melittin hybrid peptide (CEMA) with strong antimicrobial activity. This promoter-transgene combination was evaluated in transgenic tobacco (Nicotiana tabacum L. cv. Xanthi) for enhanced plant resistance against a highly virulent pathogenic fungus Fusarium solani. Transgene expression in leaves was strongly increased after fungal infection or mechanical wounding, and the accumulation of CEMA transcripts was found to be systemic and positively correlated with the number of transgene insertions. A simple and efficient in vitro regeneration bioassay for preliminary screening of transgenic lines against pathogenic fungi was developed. CEMA had strong antifungal activity in vitro, inhibiting conidia germination at concentrations that were non-toxic to tobacco protoplasts. Most importantly, the expression level of the CEMA peptide in vivo, regulated by the win3.12T promoter, was sufficient to confer resistance against F. solani in transgenic tobacco. The antifungal resistance of plants with high CEMA expression was strong and reproducible. In addition, leaf tissue extracts from transgenic plants significantly reduced the number of fungal colonies arising from germinated conidia. Accumulation of CEMA peptide in transgenic tobacco had no deleterious effect on plant growth and development. This is the first report showing the application of a heterologous pathogen-inducible promoter to direct the expression of an antimicrobial peptide in plants, and the feasibility of this approach to provide disease resistance in tobacco and, possibly, other crops.

[Anti-hepatocarcinoma effect of recombinant adenovirus carrying melittin gene].

OBJECTIVE: To find a new method of treating hepatocellular carcinoma with melittin by way of using the melittin gene. METHODS: The recombinant adenoviruses carrying the melittin gene and alpha-fetoprotein (AFP) promoter (Ad-rAFP-Mel) were constructed through a bacterial homologous recombinant system. The efficiency of the adenovirus mediated gene transfer and the inhibition effect of Ad-rAFP-Mel on the proliferation of hepatocarcinoma cells were determined by X-gal staining and MTT assay respectively. The tumorigenicity of hepatocarcinoma cells transfected by Ad-rAFP-Mel and the antitumor effect of Ad-rAFP-Mel on the transplanted tumors in nude mice were detected in vivo. RESULTS: The mRNA of the melittin gene was transcripted in HepG2 hepatocellular carcinoma cells transducted by Ad-rAFP-Mel. The efficiency of adenovirus mediated gene transfered to BEL-7402 hepatocarcinoma cells was 100% when the multiplicities of infection (MOI) of Ad-rAFP-Mel was 10 in vitro and was high in vivo as well. The inhibitive rates of Ad-rAFP-Mel and Ad-rAFP for BEL7402 cells were 66.2%+/-2.7% and 2.9%+/-2.3% (t = 30.83) by MTT assay. The inhibitive rates of Ad-CMV-Mel for BEL7402, SMMC7721 and L02 cells were 58.9%+/-9.6%, 65.9%+/-3.8%, 31.7%+/-1.2%, respectively, and those of the Ad-rAFP-Mel were 6.2%+/-2.7%, 16.1%+/-6.6%, 7.5%+/-3.3%, respectively (t = 1.27; t = 11.31, and t = 12.12, vs. Ad-CMV-Mel group in same cells). The tumorigenicity rates of hepatocarcinoma cells transfected by Ad-rAFP-Mel were decreased. A significant antineoplastic effect was detectd on transplanted tumor in nude mice by intratumoral injection of Ad-rAFP-Mel. CONCLUSION: Ad-rAFP-Mel can inhibit specifically the proliferation of AFP-producing human hepatocarcinoma cells in vitro and in vivo. It suggests that animal toxin gene can be used as an interesting antitumor gene.

[The induced apoptosis of recombinant adenovirus carrying melittin gene for hepatocellular carcinoma cell].

OBJECTIVE: To observe the induced apoptosis of recombinant adenovirus carrying melittin gene (Ad-rAFP-Mel) for hepatocellular carcinoma cell line (BEL-7402). METHODS: The morphological observe, DNA electrophoresis, TUNEL and Flow cytometry assay were used to study the apoptosis of BEL-7042 cell line transfected by Ad-rAFP-Mel. RESULTS: The morphological changes and apoptosis of BEL-7402 transfected by Ad-rAFP-Mel were confirmed with microscopy and DNA electrophoresis, TUNEL, Flow cytometry assay. The DNA ladder could be demonstrated on DNA electrophoresis in Ad-rAFP-Mel group. The apoptosis rates of BEL-7402 cells in Ad-rAFP-Mel, Ad-rAFP, and control groups were (21.5+/-2.4)%, (10.5+/-4.4)% and (3.0+/-1.4)% respectively by TUNEL assay (F = 38.0, P < 0.05) and were (7.3+/-0.5)%, (3.9+/-0.1)% and (0.8+/-0.1)% respectively by flow cytometry assay (F = 415.1, P < 0.05). CONCLUSION: It seems that melittin inducing apoptosis might be one of the antitumor mechanisms.

Bimodal regulatory effect of melittin and phospholipase A2-activating protein on human type II secretory phospholipase A2.

Melittin and phospholipase A2-activating protein (PLAP) are known as efficient activators of secretory phospholipase A2(sPLA2) types I, II, and III when phospholipid liposomes are used as substrate. The present study demonstrates that both peptides can either inhibit or activate sPLA2 depending on the peptide/phospholipid ratio when erythrocyte membranes serve as a biologically relevant substrate. Low concentrations of melittin and PLAP were observed to inhibit sPLA2-triggered release of fatty acids from erythrocyte membranes. The inhibition was reversed at melittin concentrations above 1 microM. PLAP-induced inhibition of sPLA2 persisted steadily throughout the used concentration range (0-150 nM). The two peptides induced a dose-dependent activation of sPLA2 at low concentrations, followed by inhibition when model membranes were used as substrate. This opposite modulatory effect on biological membranes and model membranes is discussed with respect to different mechanisms the interaction of the regulatory peptides with the enzyme molecules and the substrate vesicles.

Impact of infection with recombinant adenovirus carrying melittin gene on CD54 expression in HepG2 cells.

OBJECTIVE: To observe the effects of melittin gene transfection on the biological behavior of hepatocarcinoma cells. METHODS: Melittin gene was recombined into a shuttle plasmid under the control by alpha-fetoprotein (AFP) transcription regulatory element (rAFP), and the gene of interest was then recombined into an adenoviral backbone plasmid through a simplified efficient bacterial homologous recombination system. The recombinant adenoviral plasmids were subsequently linearized with Pac I and transfected into 293 cells mediated by lipofectin to generate the desired recombinant adenoviruses. After infections of the hepatocarcinoma cells with the resultant viruses carrying melittin gene was achieved, melittin gene transcription was verified by way of RT-PCR, and CD54 expression was measured by flow cytometry. RESULTS: Recombinant adenoviral vectors containing melittin gene were successfully constructed, and melittin gene transcription was approved by RT-PCR. Flow cytometry results showed that melittin gene transfection inhibited CD54 expression in the hepatocarcinoma cells. CONCLUSION: Melittin gene transfection may result in changes of the biological behavior of hepatocarcinoma cells, thus decreasing the malignancy of the tumor cells.

Induced expression of melittin, an antimicrobial peptide, inhibits infection by Chlamydia trachomatis and Mycoplasma hominis in a HeLa cell line.

As the number of pathogenic microbial strains resistant to different antibiotics increases, amphipathic peptides with antimicrobial activity are promising agents for the therapy of infectious diseases. This work deals with the effect of an amphipathic antimicrobial peptide, melittin, expressed within recombinant plasmid vectors, on infection with urogenital pathogens Chlamydia trachomatis and Mycoplasma hominis in HeLa cell culture. Recombinant plasmid constructs with the melittin gene under the control of the tetracycline-responsive promoter of human cytomegalovirus were obtained. We showed inhibition of C. trachomatis and M. hominis infection after the introduction of recombinant plasmid vectors expressing the melittin gene into the infected cell culture.

[Cloning and expression of a synthetic gene encoding magainin-melittin hybrid peptide in Escherichia coli and studies on its antibacterial activity].

A hybrid peptide gene was designed and synthesized. Its encoding peptide is constructed from residues 3-14 of magainin and residues 1-13 of melittin. The MA-E gene was cloned into plasmids pUC18 and pBV220. By DNA sequencing, the whole sequences of this gene is confirmed to be correct. The recombinant plasmid pBMA-E was expressed in E. coli DH5 alpha. A gene product band can be seen with Tricine-SDS-PAGE. The MA-E hybrid peptide was purified by immobilized metal affinity chromatography. Bioactivity assay was carried out in liquid turbidity method. The bactericide value to E. coli K12D31 is 0.182.

[Cloning of promelittin cDNA and its expression in Escherichia coli].

The cDNA encoding promelittin was obtained from the total RNA of bee poison gland by RT-PCR and was cloned to pT7Blu-T vector. The expression vector of promelittin fused with partial sequence of beta-galactosidase was constructed by ligating the fragment inserted to pUC118. Moreover, it was expressed in the strain DH5 alpha of Escherichia coli. The result of DNA sequence analysis demonstrated that the obtained cDNA sequence was same with the published one and the reading frame of fusion gene was correct.

Different bioactivities of human thyrotropin receptors with different signal peptides.

For investigation of the mechanism and pathogenesis of Graves' disease, availability of a large amount of functional human thyrotropin receptor (TSHR) capable of recognition by Graves' autoantibodies is essential. Many attempts have been made to produce the extracellular domain of TSH receptor (TSHRE) in a baculovirus expression system. However, the receptor is expressed as an insoluble form and the refolded protein is often not recognized by the autoantibodies. In this study, we found that the TSHRE expressed with its own signal peptide (VL3-RE) in insect cells is retained inside of the cells and found in both soluble and insoluble fractions in equal proportion. The signal peptide is not removed. The receptor in the soluble fraction is not recognized by either TSH or Graves' autoantibodies. The TSHRE with an insect-specific mellitin signal peptide (Mel-RE) is also retained inside of the cell and found in both the soluble and insoluble fractions in equal proportion. However, the signal peptide is removed and the receptor is recognized by the Graves' autoantibodies but not by TSH. Also, the amount of Mel-RE expressed was 5-10-fold higher than VL3-RE. The two receptor preparations apparently have the same degree of glycosylation as evidenced by the same increased mass (approximately 15 kDa) due to glycosylation. However, the two receptors have different affinity for an anion-exchange resin and different pI. Deglycosylated receptors have the same pI. This suggests that the composition of sugars may be different. Taken together, the results suggest that the two receptors are modified and folded differently by different pathways due to the presence of different signal peptides. Use of an insect-specific signal peptide is recommended for expression of TSHR that is recognized by Graves' autoantibodies in a baculovirus system.

Melittin synthesis in the venom system of the honey bee (Apis mellifera L.).

The amount of melittin (measured by a direct hemolytic assay) contained in the venom system of single honey bees (Apis mellifera), of known age, increases from the time of eclosion to an age of about 4 weeks when about 500 micrograms of melittin is present. In older bees (5-6 weeks) the melittin level falls to about 250 micrograms. Measurements of the incorporation of [3H]leucine (injected into the haemolymph) into melittin show that melittin synthesis is most active in bees aged between 1 and 2 weeks after eclosion. The melittin content of the venom system changes as the summer progresses. Melittin levels in a bee of any age greater than 1 week are lower in mid-August than in a bee of the same age in early June.

Expression of honeybee prepromelittin as a fusion protein in Escherichia coli.

Strategies for the expression of precursors of eukaryotic secreted proteins as part of fused proteins in Escherichia coli have been explored. A fusion protein with beta-galactosidase at the N-terminal end and honeybee prepromelittin at the C-terminal end (beta-gal-pM) was expressed in low amounts as a cleaved polypeptide, from which the promelittin portion had been removed. Inclusion in the induction culture of 10 mM MgCl2 or 8.3% (v/v) ethanol, inhibitors of signal peptidase, gave rise to the full-length beta-gal-pM fusion protein. The results suggest that a soluble recombinant fusion protein with a signal peptide in an internal location 660 residues from the N-terminus is recognized by the E. coli translocation apparatus in the inner membrane and by leader peptidase. High-level production (about 45% of total cellular proteins) of prepromelittin was achieved when it was part of a fusion protein at the C-terminus of a truncated insoluble polypeptide from bacteriophage gene 10. This fusion protein separated into inclusion bodies in an aggregated form. In contrast, attempts to express prepromelittin by itself or at the N-terminal end of a fusion with mouse dihydrofolate reductase (pM-DHFR) proved unsuccessful.

Enhanced secretion from insect cells of a foreign protein fused to the honeybee melittin signal peptide.

The baculovirus/insect cell system has been remarkably successful in yielding high levels of synthesis of many proteins which have been difficult to synthesize in other host/vector systems. The system is also capable of secreting heterologous proteins, but with generally low efficiency. We have increased the efficiency of secretion of the system by using signal peptides of insect origin to direct the secretion of a foreign protein. The precursor of the plant cysteine protease papain (propapain) has been used as a report enzyme to compare secretion efficiency. Insect cells infected with a baculovirus recombined with the gene encoding propapain fused to the sequence encoding the honeybee melittin signal peptide secreted over five times more papain precursor than the wild-type prepropapain which used the plant signal peptide. Based on these results, we have assembled pVT-Bac, an Autographa californica nuclear polyhedrosis virus transfer vector that may enhance secretion of other foreign proteins from insect cells. The vector incorporates a number of features: phage f1 ori to facilitate site-directed mutagenesis, the strong polyhedrin promoter upstream from the melittin signal peptide-encoding sequence, and eight unique restriction sites to facilitate fusion of heterologous genes.

Export of honeybee prepromelittin in Escherichia coli depends on the membrane potential but does not depend on proteins secA and secY.

Honeybee prepromelittin (70 amino acid residues), the precursor of an eukaryotic secretory protein, and a hybrid protein between prepromelittin and mouse dihydrofolate reductase (257 amino acid residues) were expressed in Escherichia coli and characterized with respect to their requirements for transport across the plasma membrane. Both precursor proteins are posttranslationally processed and exported into the periplasm, and they both depend on the membrane potential for this to occur. With respect to dependence on components of the export machinery, however, the two precursor proteins show striking differences: the small precursor protein prepromelittin does not require the function of proteins secA and secY; the large precursor protein prepromelittin-dihydrofolate reductase, on the other hand, depends on both components. The implications of these observations with respect to the mechanisms of protein export in E. coli and of protein import into the endoplasmic reticulum are discussed.