A novel family of defensin-like peptides from Hermetia illucens with antibacterial properties

BACKGROUND

The world faces a major infectious disease challenge. Interest in the discovery, design, or development of antimicrobial peptides (AMPs) as an alternative approach for the treatment of bacterial infections has increased. Insects are a good source of AMPs which are the main effector molecules of their innate immune system. Black Soldier Fly Larvae (BSFL) are being developed for large-scale rearing for food sustainability, waste reduction and as sustainable animal and fish feed. Bioinformatic studies have suggested that BSFL have the largest number of AMPs identified in insects. However, most AMPs identified in BSF have not yet undergone antimicrobial evaluation but are promising leads to treat critical infections.

RESULTS

Jg7197.t1, Jg7902.t1 and Jg7904.t1 were expressed into the haemolymph of larvae following infection with Salmonella enterica serovar Typhimurium and were predicted to be AMPs using the computational tool ampir. The genes encoding these proteins were within 2 distinct clusters in chromosome 1 of the BSF genome. Following removal of signal peptides, predicted structures of the mature proteins were superimposed, highlighting a high degree of structural conservation. The 3 AMPs share primary sequences with proteins that contain a Kunitz-binding domain; characterised for inhibitory action against proteases, and antimicrobial activities. An in vitro antimicrobial screen indicated that heterologously expressed SUMO-Jg7197.t1 and SUMO-Jg7902.t1 did not show activity against 12 bacterial strains. While recombinant SUMO-Jg7904.t1 had antimicrobial activity against a range of Gram-negative and Gram-positive bacteria, including the serious pathogen Pseudomonas aeruginosa.

CONCLUSIONS

We have cloned and purified putative AMPs from BSFL and performed initial in vitro experiments to evaluate their antimicrobial activity. In doing so, we have identified a putative novel defensin-like AMP, Jg7904.t1, encoded in a paralogous gene cluster, with antimicrobial activity against P. aeruginosa.

Class I defensins (BraDef) from broccoli (Brassica oleracea var. italica) seeds and their antimicrobial activity

The objective of this study was to determine whether seeds of Brassica oleracea var. italica (i.e. broccoli, an edible plant) produce defensins that inhibit phytopathogenic fungi and pathogenic bacteria of clinical significance. Crude extracts obtained from broccoli seeds were fractioned by molecular exclusion techniques and analyzed by liquid chromatography-high-resolution mass spectrometry. Two peptides were identified, BraDef1 (10.68 kDa) and BraDef2 (9.9 kDa), which were categorized as Class I defensins based on (a) their primary structure, (b) the presence of four putative cysteine disulfide bridges, and (c) molecular modeling predictions. BraDef1 and BraDef2 show identities of, respectively, 98 and 71%, and 67 and 85%, with defensins from Brassica napus and Arabidopsis thaliana. BraDef (BraDef1 + BraDef2) disrupted membranes of Colletotrichum gloeosporioides and Alternaria alternata and also reduced hyphal growth of C. gloeosporioides by ~ 56% after 120 h of incubation. Pathogenic bacteria (Bacillus cereus 183, Listeria monocytogenes, Salmonella typhimurium, Pseudomonas aeruginosa, and Vibrio parahaemolitycus) were susceptible to BraDef, but probiotic bacteria such as Bifidobacterium animalis, Lactobacillus acidophilus, and Lactobacillus casei were not inhibited. To our knowledge, this is the first report of defensins present in seeds of B. oleracea var. italica (i.e. edible broccoli). Our findings suggest an applied value for BraDef1/BraDef2 in controlling phytopathogenic fungi and pathogenic bacteria of clinical significance.

A novel recombinant javanicin with dual antifungal and anti-proliferative activities

Resistance to common drugs by microorganisms and cancers has become a major issue in modern healthcare, increasing the number of deaths worldwide. Novel therapeutic agents with a higher efficiency and less side effects for the treatment of certain diseases are urgently needed. Plant defensins have an integral role in a hosts' immune system and are attractive candidates for combatting drug-resistant microorganisms. Interestingly, some of these defensins also showed great potential due to their cytotoxic activity toward cancer cells. In this study, a defensin encoding gene was isolated from five legume seeds using 3' rapid amplification of cDNA ends (3' RACE) with degenerate primers and cDNA cloning strategies. Bioinformatic tools were used for in silico identification and the characterization of new sequences. To study the functional characteristics of these unique defensins, the gene encoded for Sesbania javanica defensin, designated as javanicin, was cloned into pTXB-1 plasmid and expressed in the Escherichia coli Origami 2 (DE3) strain. Under optimized conditions, a 34-kDa javanicin-intein fusion protein was expressed and approximately 2.5-3.5 mg/L of soluble recombinant javanicin was successfully extracted with over 90% purity. Recombinant javanicin displayed antifungal properties against human pathogenic fungi, including resistant strains, as well as cytotoxic activities toward the human breast cancer cell lines, MCF-7 & MDA-MB-231. Recombinant javanicin holds great promise as a novel therapeutic agent for further medical applications.

Molecular characterization and protein localization of the antimicrobial peptide big defensin from the scallop Argopecten purpuratus after Vibrio splendidus challenge

Big defensins are antimicrobial peptides (AMPs) that are proposed as important effectors of the immune response in mollusks, chelicerates and chordates. At present, only two members of the big defensin family have been identified in scallop. In the present work, a cDNA sequence encoding a new big defensin homologue was characterized from the scallop Argopecten purpuratus, namely ApBD1. ApBD1 cDNA sequence comprised 585 nucleotides, with an open reading frame of 375 bp and 5'- and 3'-UTRs of 41 and 167 bp, respectively. The deduced protein sequence contains 124 amino acids with a molecular weight of 13.5 kDa, showing characteristic motifs of the big defensin family and presenting 76% identity with the big defensin from the scallop A. irradians. Phylogenetic analysis revealed that ApBD1 is included into the cluster of big defensins from mollusks. Tissue-specific transcript expression analysis by RT-qPCR showed that ApBD1 was present in all tissues tested from non-immune challenged scallops but it was most strongly expressed in the mantle. The transcript levels of ApBD1 were significantly up-regulated in gills at 24 and 48 h post-injection with the heat-attenuated bacteria Vibrio splendidus. Additionally, immunofluorescence analysis using a polyclonal anti-ApBD1 antibody showed that this protein was abundantly located in epithelial linings of gills and mantle; and also in digestive gland showing ApBD1-infiltrating hemocytes from immune challenged scallops. This is the first time that a big defensin is detected and located at the protein level in a mollusk. These results suggest an important role of ApBD1 in the mucosal immune response of A. purpuratus.

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

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

Two novel antimicrobial defensins from rice identified by gene coexpression network analyses

Defensins form an antimicrobial peptides (AMP) family, and have been widely studied in various plants because of their considerable inhibitory functions. However, their roles in rice (Oryza sativa L.) have not been characterized, even though rice is one of the most important staple crops that is susceptible to damaging infections. Additionally, a previous study identified 598 rice genes encoding cysteine-rich peptides, suggesting there are several uncharacterized AMPs in rice. We performed in silico gene expression and coexpression network analyses of all genes encoding defensin and defensin-like peptides, and determined that OsDEF7 and OsDEF8 are coexpressed with pathogen-responsive genes. Recombinant OsDEF7 and OsDEF8 could form homodimers. They inhibited the growth of the bacteria Xanthomonas oryzae pv. oryzae, X. oryzae pv. oryzicola, and Erwinia carotovora subsp. atroseptica with minimum inhibitory concentration (MIC) ranging from 0.6 to 63μg/mL. However, these OsDEFs are weakly active against the phytopathogenic fungi Helminthosporium oryzae and Fusarium oxysporum f.sp. cubense. This study describes a useful method for identifying potential plant AMPs with biological activities.

Purification and characterization of a novel antibacterial peptide from black soldier fly (Hermetia illucens) larvae

In this study, we induced and purified a novel antimicrobial peptide exhibiting activity against Gram-positive bacteria from the immunized hemolymph of Hermetia illucens larvae. The immunized hemolymph was extracted, and the novel defensin-like peptide 4 (DLP4) was purified using solid-phase extraction and reverse-phase chromatography. The purified DLP4 demonstrated a molecular weight of 4267 Da, as determined using the matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) method. From analysis of DLP4 by N-terminal amino acid sequencing using Edman degradation, combined with MALDI-TOF and rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR), the amino acid sequence of the mature peptide was determined to be ATCDLLSPFKVGHAACAAHCIARGKRGGWCDKRAVCNCRK. In NCBI BLAST, the amino acid sequence of DPL4 was found to be 75% identical to the Phlebotomus duboscqi defensin. Analysis of the minimal inhibitory concentration (MIC) revealed that DLP4 have antibacterial effects against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). The expression of DLP4 transcripts in several tissues after bacterial challenge was measured by quantitative real-time PCR. Expression of the DLP4 gene hardly occurred throughout the body before immunization, but was mostly evident in the fat body after immunization.

Isolation of a Hemagglutinin with Potent Antiproliferative Activity and a Large Antifungal Defensin from Phaseolus vulgaris cv. Hokkaido Large Pinto Beans

Lectins (hemagglutinins) are defined as sugar-binding proteins or glycoproteins with various biological activities. A 60 kDa dimeric hemagglutinin with a blocked N-terminus was isolated in large yield (190 mg/60 g) from the common edible bean Phaseolus vulgaris cv. Hokkaido large pinto bean. Its hemagglutinating, antifungal, and antitumor activities as well as the effects of carbohydrate and metal ions on its hemagglutinating activity were examined. It inhibited the proliferation of nasopharyngeal carcinoma (CNE2), human breast cancer (MCF7), and hepatoma (HepG2) cells. The IC50 values toward HepG2, MCF7, and CNE2 cells after treatment for 48 h were 8.1, 6.07, and 7.49 μM, respectively, which were relatively low among lectins of different P. vulgaris cultivars. From the pinto beans, a 10888 Da antifungal peptide with similarity to plant defensins as revealed by mass spectroscopic analysis was also isolated with a yield of 3.2 mg of proteins from 60 g of beans. The large defensin was capable of inhibiting mycelial growth in Mycosphaerella arachidicola, Setosphaeria turcica, Bipolaris maydis, and Fusarium oxysporum but not in Valsa mali.

[Effect of thrombodefensins on the course of chronic staphylococci dermatitis on in vivo model]

AIM

Evaluate therapeutic effect of thrombodefensins (TD) on the course of chronic staphylococci dermatitis (CSD) in mice.

MATERIALS AND METHODS

TD was obtained from human thrombocytes. 24 CBRB-Rb(8.17)1Iem line female mice were used in the experiment, that were divided into 2 equal groups. Staphylococcus aureus strain producing exfoliative exotoxin was isolated from withers of each mouse with signs of affection. Mice of the experiment group subcutaneously around the locus of affection, received for 4 weeks daily a composition in the volume of 0.2 ml, that contains 1 g of dry lyophilized TD diluted in 10 ml of 0.9% NaCl (final concentration of the preparation--15 μg/ml). Control group animals similarly received 0.9% solution of NaCl without TD. Area and degree of the affected zone on the back was evaluated in all the mice. Statistical significance of differences in the values of parameters was determined by t-criteria.

RESULTS

At the start of the experiment the average area of the affected zone in mice of both groups was 167 ± 17 mm2. From day 8 to 23 the expansion of the affection zone was observed, however in the experiment group of mice these negative tendencies were less pronounced. At the end of the experiment on day 50 the area of affection was significantly smaller (2.3 times) in the experiment group of mice compared with the control (p < 0.05).

CONCLUSION

The anti-staphylococci effect of TD, demonstrated in the study, opens perspective of their clinical use in CSD therapy.

Defensin from the ornate sheep tick Dermacentor marginatus and its effect on Lyme borreliosis spirochetes

Expression of the previously reported defensin of the tick Dermacentor marginatus (defDM) was analysed in different organs by RT-PCR. mRNA of the defDM gene was detected in the hemolymph, midgut and salivary glands. Moreover defDM was isolated from the tick hemolymph using RP-HPLC and its sequence was determined by mass spectrometry and Edman degradation. Synthetic peptide was used for determining biological activities. The results showed an anti-Gram-positive bacterial role for the defensin. As D. marginatus ticks appear not to be vectors of the Lyme disease agent of the complex Borrelia burgdorferi sensu lato, we tested the influence of defDM on Borrelia afzelii. There is a very clear borrelicidal activity of the defensin, which is concentration dependent and suggests a possible role in the clearing of Borrelia ingested by D. marginatus ticks.

Lysozyme and defense peptides as suppressors of phenoloxidase activity in Galleria mellonella

The prophenoloxidase (proPO) cascade supplies quinones and other reactive compounds for melanin formation, protein cross-linking, hemolymph coagulation, and killing of microbial invaders as well as parasites. The high cytotoxicity of the generated compounds requires a strict control of the activation of the proPO system and phenoloxidase (PO) activity to minimize damage to host tissues and cells. The PO activity in hemolymph of Escherichia coli challenged Galleria mellonella larvae increased, with a temporal drop 1 h after the challenge, reaching the highest level 24 h after the challenge. In the present study, a potential role of G. mellonella defense peptides and lysozyme in controlling the proPO system was investigated. The effects of purified defense peptides (anionic peptides 1 and 2, cecropin D-like peptide, Galleria defensin, proline-rich peptides 1 and 2) and lysozyme were analyzed. Four compounds, namely lysozyme, Galleria defensin, proline-rich peptide 1, and anionic peptide 2, decreased the hemolymph PO activity considerably, whereas the others did not affect the enzyme activity level. Our results indicate that these hemolymph factors could play multiple and distinct roles in the insect immune response.

Phosphoinositide-mediated oligomerization of a defensin induces cell lysis

Cationic antimicrobial peptides (CAPs) such as defensins are ubiquitously found innate immune molecules that often exhibit broad activity against microbial pathogens and mammalian tumor cells. Many CAPs act at the plasma membrane of cells leading to membrane destabilization and permeabilization. In this study, we describe a novel cell lysis mechanism for fungal and tumor cells by the plant defensin NaD1 that acts via direct binding to the plasma membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2). We determined the crystal structure of a NaD1:PIP2 complex, revealing a striking oligomeric arrangement comprising seven dimers of NaD1 that cooperatively bind the anionic headgroups of 14 PIP2 molecules through a unique 'cationic grip' configuration. Site-directed mutagenesis of NaD1 confirms that PIP2-mediated oligomerization is important for fungal and tumor cell permeabilization. These observations identify an innate recognition system by NaD1 for direct binding of PIP2 that permeabilizes cells via a novel membrane disrupting mechanism. DOI: http://dx.doi.org/10.7554/eLife.01808.001.

Inhibition of cereal rust fungi by both class I and II defensins derived from the flowers of Nicotiana alata

Defensins are a large family of small, cysteine-rich, basic proteins, produced by most plants and plant tissues. They have a primary function in defence against fungal disease, although other functions have been described. This study reports the isolation and characterization of a class I secreted defensin (NaD2) from the flowers of Nicotiana alata, and compares its antifungal activity with the class II defensin (NaD1) from N. alata flowers, which is stored in the vacuole. NaD2, like all other class I defensins, lacks the C-terminal pro-peptide (CTPP) characteristic of class II defensins. NaD2 is most closely related to Nt-thionin from N. tabacum (96% identical) and shares 81% identity with MtDef4 from alfalfa. The concentration required to inhibit in vitro fungal growth by 50% (IC50 ) was assessed for both NaD1 and NaD2 for the biotrophic basidiomycete fungi Puccinia coronata f. sp. avenae (Pca) and P. sorghi (Ps), the necrotrophic pathogenic ascomycetes Fusarium oxysporum f. sp. vasinfectum (Fov), F. graminearum (Fgr), Verticillium dahliae (Vd) and Thielaviopsis basicola (Tb), and the saprobe Aspergillus nidulans. NaD1 was a more potent antifungal molecule than NaD2 against both the biotrophic and necrotrophic fungal pathogens tested. NaD2 was 5-10 times less effective at killing necrotrophs, but only two-fold less effective on Puccinia species. A new procedure for testing antifungal proteins is described in this study which is applicable to pathogens with spores that are not amenable to liquid culture, such as rust pathogens. Rusts are the most damaging fungal pathogens of many agronomically important crop species (wheat, barley, oats and soybean). NaD1 and NaD2 inhibited urediniospore germination, germ tube growth and germ tube differentiation (appressoria induction) of both Puccinia species tested. NaD1 and NaD2 were fungicidal on Puccinia species and produced stunted germ tubes with a granular cytoplasm. When NaD1 and NaD2 were sprayed onto susceptible oat plants prior to the plants being inoculated with crown rust, they reduced the number of pustules per leaf area, as well as the amount of chlorosis induced by infection. Similar to observations in vitro, NaD1 was more effective as an antifungal control agent than NaD2. Further investigation revealed that both NaD1 and NaD2 permeabilized the plasma membranes of Puccinia spp. This study provides evidence that both secreted (NaD2) and nonsecreted (NaD1) defensins may be useful for broad-spectrum resistance to pathogens.

Identification and mechanism of action of the plant defensin NaD1 as a new member of the antifungal drug arsenal against Candida albicans

In recent decades, pathogenic fungi have become a serious threat to human health, leading to major efforts aimed at characterizing new agents for improved treatments. Promising in this context are antimicrobial peptides produced by animals and plants as part of innate immune systems. Here, we describe an antifungal defensin, NaD1, with activity against the major human pathogen Candida albicans, characterize the mechanism of killing, and identify protection strategies used by the fungus to survive defensin treatment. The mechanism involves interaction between NaD1 and the fungal cell surface followed by membrane permeabilization, entry into the cytoplasm, hyperproduction of reactive oxygen species, and killing induced by oxidative damage. By screening C. albicans mutant libraries, we identified that the high-osmolarity glycerol (HOG) pathway has a unique role in protection against NaD1, while several other stress-responsive pathways are dispensable. The involvement of the HOG pathway is consistent with induction of oxidative stress by NaD1. The HOG pathway has been reported to have a major role in protection of fungi against osmotic stress, but our data indicate that osmotic stress does not contribute significantly to the adverse effects of NaD1 on C. albicans. Our data, together with previous studies with human beta-defensins and salivary histatin 5, indicate that inhibition of the HOG pathway holds promise as a broad strategy for increasing the activity of antimicrobial peptides against C. albicans.

Expression and characterization of a novel scorpine-like peptide Ev37, from the scorpion Euscorpiops validus

Scorpion venom contains a group of two-domain peptides that function to block potassium channels or have cytolytic activities. These peptides, whose functions are poorly studied, are named β-KTx or scorpine-like peptides. Ev37, the first identified gene in the Euscorpiidae family, which encoded a novel scorpine-like peptide, was cloned from the venom cDNA library of scorpion Euscorpiops validus. Sequence analysis showed that the mature Ev37 peptide contained 78 amino acid residues, which formed two structural domains: a putative α-helical N-terminus and a C-terminus with the cysteine-stabilized α/β motif. The peptide rEv37 and two truncated peptides representing the individual structural domains (Ev37-N and Ev37-C) were expressed in Escherichia coli and purified for functional study. Unlike classic scorpine-like peptides, rEv37 and truncated peptides showed no cytolytic activity against bacteria or eukaryotic cells. Interestingly, rEv37 selectively inhibited Kv1.3 channel without effectively blocking Kv1.1 and Kv1.2 channels. Neither Ev37-N nor Ev37-C blocked Kv1.3 channel, suggesting that both the N-terminal and C-terminal domain of Ev37 are likely involved in the interaction with Kv1.3 channel. These results not only enrich our knowledge of scorpion toxins from scorpine-like subfamily but also provide a novel template with unique structure for designing new types of selective Kv1.3 blockers.

Anti-Legionella dumoffii activity of Galleria mellonella defensin and apolipophorin III

The gram-negative bacterium Legionella dumoffii is, beside Legionella pneumophila, an etiological agent of Legionnaires’ disease, an atypical form of pneumonia. The aim of this study was to determine the antimicrobial activity of Galleria mellonella defense polypeptides against L. dumoffii. The extract of immune hemolymph, containing a mixture of defense peptides and proteins, exhibited a dose-dependent bactericidal effect on L. dumoffii. The bacterium appeared sensitive to a main component of the hemolymph extract, apolipophorin III, as well as to a defense peptide, Galleria defensin, used at the concentrations 0.4 mg/mL and 40 μg/mL, respectively. L. dumoffii cells cultured in the presence of choline were more susceptible to both defense factors analyzed. A transmission electron microscopy study of bacterial cells demonstrated that Galleria defensin and apolipophorin III induced irreversible cell wall damage and strong intracellular alterations, i.e., increased vacuolization, cytoplasm condensation and the appearance of electron-white spaces in electron micrographs. Our findings suggest that insects, such as G. mellonella, with their great diversity of antimicrobial factors, can serve as a rich source of compounds for the testing of Legionella susceptibility to defense-related peptides and proteins.

An antifungal peptide from Phaseolus vulgaris cv. brown kidney bean

A 5.4-kDa antifungal peptide, with an N-terminal sequence highly homologous to defensins and inhibitory activity against Mycosphaerella arachidicola (IC(50)= 3 μM), Setospaeria turcica and Bipolaris maydis, was isolated from the seeds of Phaseolus vulgaris cv. brown kidney bean. The peptide was purified by employing a protocol that entailed adsorption on Affi-gel blue gel and Mono S and finally gel filtration on Superdex 75. The antifungal activity of the peptide against M. arachidicola was stable in the pH range 3-12 and in the temperature range 0°C to 80°C. There was a slight reduction of the antifungal activity at pH 2 and 13, and the activity was indiscernible at pH 0, 1, and 14. The activity at 90°C and 100°C was slightly diminished. Deposition of Congo red at the hyphal tips of M. arachidicola was induced by the peptide indicating inhibition of hyphal growth. The lack of antiproliferative activity of brown kidney bean antifungal peptide toward tumor cells, in contrast to the presence of such activity of other antifungal peptides, indicates that different domains are responsible for the antifungal and antiproliferative activities.

The defensin gene family expansion in the tick Ixodes scapularis

Ixodid ticks transmit a variety of pathogens by blood feeding. Here, we report computational identification of two multigene families of defensin-like peptides (DLPs) in the Ixodes scapularis genome, one corresponding to scapularisin and the other named scasin. Members in the scapularisin family share high sequence similarity to some antibacterial ancient invertebrate-type defensins (AITDs) isolated from primitive insects, arachnids, bivalvia, and fungi whereas scasins represent a novel family of DLPs identified by their overall acidic molecular surface and low sequence similarity to any known defensins. Codon-substitution models support neutral evolution in scapularisins but strong positive selection signal was found throughout the molecules of scasins. The synthetic γ-core region of scapularisin-20 exhibits a wide-spectrum of antimicrobial activity at micromolar concentrations. The finding of extensive gene expansion of DLPs in a vector arachnida may be valuable in the understanding of its role in pathogen transmission.

Structure-activity determinants in antifungal plant defensins MsDef1 and MtDef4 with different modes of action against Fusarium graminearum

Plant defensins are small cysteine-rich antimicrobial proteins. Their three-dimensional structures are similar in that they consist of an α-helix and three anti-parallel β-strands stabilized by four disulfide bonds. Plant defensins MsDef1 and MtDef4 are potent inhibitors of the growth of several filamentous fungi including Fusarium graminearum. However, they differ markedly in their antifungal properties as well as modes of antifungal action. MsDef1 induces prolific hyperbranching of fungal hyphae, whereas MtDef4 does not. Both defensins contain a highly conserved γ-core motif (GXCX_3–9C), a hallmark signature present in the disulfide-stabilized antimicrobial peptides, composed of β2 and β3 strands and the interposed loop. The γ-core motifs of these two defensins differ significantly in their primary amino acid sequences and in their net charge. In this study, we have found that the major determinants of the antifungal activity and morphogenicity of these defensins reside in their γ-core motifs. The MsDef1-γ4 variant in which the γ-core motif of MsDef1 was replaced by that of MtDef4 was almost as potent as MtDef4 and also failed to induce hyperbranching of fungal hyphae. Importantly, the γ-core motif of MtDef4 alone was capable of inhibiting fungal growth, but that of MsDef1 was not. The analysis of synthetic γ-core variants of MtDef4 indicated that the cationic and hydrophobic amino acids were important for antifungal activity. Both MsDef1 and MtDef4 induced plasma membrane permeabilization; however, kinetic studies revealed that MtDef4 was more efficient in permeabilizing fungal plasma membrane than MsDef1. Furthermore, the in vitro antifungal activity of MsDef1, MsDef1-γ4, MtDef4 and peptides derived from the γ-core motif of each defensin was not solely dependent on their ability to permeabilize the fungal plasma membrane. The data reported here indicate that the γ-core motif defines the unique antifungal properties of each defensin and may facilitate de novo design of more potent antifungal peptides.

Novel antifungal defensins from Nigella sativa L. seeds

From seeds of Nigella sativa L. (Ranunculaceae), an endemic plant of Uzbekistan, two novel defensins named Ns-D1 and Ns-D2, were isolated and sequenced. The peptides differ by a single amino acid residue and show high sequence similarity to Raphanus sativus L. defensins Rs-AFP1 and Rs-AFP2. The Ns-D1 and Ns-D2 defensins display strong although divergent antifungal activity towards a number of phytopathogenic fungi. High antifungal activity of N. sativa defensins makes them promising candidates for engineering pathogen-resistant plants.

An antifungal defensin from Phaseolus vulgaris cv. 'Cloud Bean'

An antifungal peptide with a defensin-like sequence and exhibiting a molecular mass of 7.3kDa was purified from dried seeds of Phaseolus vulgaris 'Cloud Bean'. The isolation procedure entailed anion exchange chromatography on DEAE-cellulose, affinity chromatography an Affi-gel blue gel, cation exchange chromatography on SP-Sepharose, and gel filtration by fast protein liquid chromatography on Superdex 75. Although the antifungal peptide was unadsorbed on DEAE-cellulose, it was adsorbed on both Affi-gel blue gel and SP-Sepharose. The antifungal peptide exerted antifungal activity against Mycosphaerella arachidicola with an IC(50) value of 1.8 μM. It was also active against Fusarium oxysporum with an IC(50) value of 2.2 μM. It had no inhibitory effect on HIV-1 reverse transcriptase when tested up to 100 μM. Proliferation of L1210 mouse leukemia cells and MBL2 lymphoma cells was inhibited by the antifungal peptide with an IC(50) of 10 μM and 40 μM, respectively.

Expression and characterization of antimicrobial peptides Retrocyclin-101 and Protegrin-1 in chloroplasts to control viral and bacterial infections

Retrocyclin-101 (RC101) and Protegrin-1 (PG1) are two important antimicrobial peptides that can be used as therapeutic agents against bacterial and/or viral infections, especially those caused by the HIV-1 or sexually transmitted bacteria. Because of their antimicrobial activity and complex secondary structures, they have not yet been produced in microbial systems and their chemical synthesis is prohibitively expensive. Therefore, we created chloroplast transformation vectors with the RC101 or PG1 coding sequence, fused with GFP to confer stability, furin or Factor Xa cleavage site to liberate the mature peptide from their fusion proteins and a His-tag to aid in their purification. Stable integration of RC101 into the tobacco chloroplast genome and homoplasmy were confirmed by Southern blots. RC101 and PG1 accumulated up to 32%-38% and 17%∼26% of the total soluble protein. Both RC101 and PG1 were cleaved from GFP by corresponding proteases in vitro, and Factor Xa-like protease activity was observed within chloroplasts. Confocal microscopy studies showed location of GFP fluorescence within chloroplasts. Organic extraction resulted in 10.6-fold higher yield of RC101 than purification by affinity chromatography using His-tag. In planta bioassays with Erwinia carotovora confirmed the antibacterial activity of RC101 and PG1 expressed in chloroplasts. RC101 transplastomic plants were resistant to tobacco mosaic virus infections, confirming antiviral activity. Because RC101 and PG1 have not yet been produced in other cell culture or microbial systems, chloroplasts can be used as bioreactors for producing these proteins. Adequate yield of purified antimicrobial peptides from transplastomic plants should facilitate further preclinical studies.

Purification of antimicrobial peptides from human skin

Human skin is a rich source of human antimicrobial peptides. Its cellular source is the keratinocyte, which terminally differentiates in the uppermost parts of the skin, eventually forming the stratum corneum, the horny layer. The easy availability of human stratum corneum makes it possible to identify and characterize human antimicrobial peptides with a biochemical approach. Moreover, the availability of lesional scales of patients with psoriasis, an inflammatory skin disease, allows the identification of human-inducible peptide antibiotics, which are absent in healthy skin. With this strategy, the beta-defensins hBD-2 and hBD-3, RNase-7 as well as psoriasin/S100A7 have been discovered as human antimicrobial peptides and proteins. A detailed description of the strategies and methods is presented, which allowed a successful identification and characterization of human antimicrobial peptides. We used various HPLC techniques, combined with antimicrobial testing as read-out system. In parallel, SDS-PAGE analyses as well as electrospray ionization mass spectrometry were used for further biochemical characterization as well as purity assessment.

PDC1, a corn defensin peptide expressed in Escherichia coli and Pichia pastoris inhibits growth of Fusarium graminearum

Plant defensin corn 1 (Pdc1) gene was amplified from corn genomic DNA with the primers designed from a corn EST sequence homologous to a barley defensin gene. The cloned gene contains two exons and an intron. The deduced 9KDa PDC1 peptide has a sequence that is identical to corn gamma2-zeathionin and has the typical features of a plant defensin, including a signal sequence of 35 amino acids, followed by a characteristic defensin domain of 47 amino acids containing 8 cysteines. The defensin protein was expressed from the cloned cDNA introduced into two different expression systems; prokaryotic, Escherichia coli and eukaryotic, yeast (Pichia pastoris). The PDC1 protein was purified with a nickel resin column and was tested for its antifungal activities using the pathogen Fusarium graminearum. The protein expressed in both E. coli and P. pastoris had antifungal activity, however the protein expressed in P. pastoris was more efficient in inhibiting growth of F. graminearum. FTIR analysis of PDC1 protein expressed in the two expression systems showed that expression in P. pastoris gave a product with more beta-sheets and less random unordered structure than when it was expressed in E. coli. In addition, removal of the His-tag used for purification increased the fungicidal activity of the PDC1 protein. The data presented here suggest that the defensin PDC1 peptide of corn could be effectively used to restrict the disease caused by F. graminearum.

Isolation, characterization and cloning of a cDNA encoding a new antifungal defensin from Phaseolus vulgaris L. seeds

The PvD1 defensin was purified from Phaseolus vulgaris (cv. Pérola) seeds, basically as described by Terras et al. [Terras FRG, Schoofs HME, De Bolle MFC, Van Leuven F, Ress SB, Vanderleyden J, Cammue BPA, Broekaer TWF. Analysis of two novel classes of plant antifungal proteins from radish (Raphanus sativus L.) seeds. J Biol Chem 1992;267(22):15301-9], with some modifications. A DEAE-Sepharose, equilibrated with 20mM Tris-HCl, pH 8.0, was initially utilized for the separation of peptides after ammonium sulfate fractionation. The basic fraction (the non-retained peak) obtained showed the presence of one unique band in SDS-Tricine gel electrophoresis with a molecular mass of approximately 6kDa. The purification of this peptide was confirmed after a reverse-phase chromatography in a C2/C18 column by HPLC, where once again only one peak was observed and denominated H1. H1 was submitted to N-terminal sequencing and the comparative analysis in databanks revealed high similarity with sequences of different defensins isolated from other plants species. The N-terminal sequence of the mature defensin isolated was used to produce a degenerated primer. This primer allowed the amplification of the defensin cDNA by RT-PCR from mRNA of P. vulgaris seeds. The sequence analysis of the cloned cDNA, named PVD1, demonstrated 314bp encoding a polypeptide of 47 amino acids. The deduced peptide presented high similarity with plant defensins of Vigna unguiculata (93%), Cicer arietinum (95%) and Pachyrhizus erosus (87%). PvD1 inhibited the growth of the yeasts, Candida albicans, Candida parapsilosis, Candida tropicalis, Candida guilliermondii, Kluyveromyces marxiannus and Saccharomyces cerevisiae. PvD1 also presented an inhibitory activity against the growth of phytopathogenic fungi including Fusarium oxysporum, Fusarium solani, Fusarium lateritium and Rizoctonia solani.

Evolutionary relationship between defensins in the Poaceae family strengthened by the characterization of new sugarcane defensins

Plant defensins are small (45-54 amino acids), highly basic, cysteine-rich peptides structurally related to defensins of other organisms, including insects and mammals. Small putative proteins (MW < 10 kDa) containing eight cysteines were screened based on the sugarcane expressed sequence tag (EST) database. We selected ORFs that exhibited 25-100% similarity in primary sequence with other defensins in the NCBI database and that contained eight cysteines. This similarity is sufficient for folding prediction, but not enough for biological activity inference. Six putative defensins (Sd1-6) were selected, and activity assays showed that recombinant Sd1, Sd3 and Sd5 are active against fungi, but not against bacteria. Structural characterization, based on circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy showed that the structures of these Sds were compatible with alpha/beta proteins, a feature expected for plant defensins. Phylogenetic analysis revealed that sugarcane defensins could clearly be grouped within defensins from Poaceae family and Andropogoneae tribe. Our work demonstrates that defensins show strong conservation in the Poaceae family and may indicate that the same conservation occurs in other families. We suggest that evolutionary relationships within plant families can be used as a procedure to predict and annotate new defensins in genomes and group them in evolutionary classes to help in the investigation of their biological function.

Vv-AMP1, a ripening induced peptide from Vitis vinifera shows strong antifungal activity

BACKGROUND

Latest research shows that small antimicrobial peptides play a role in the innate defense system of plants. These peptides typically contribute to preformed defense by developing protective barriers around germinating seeds or between different tissue layers within plant organs. The encoding genes could also be upregulated by abiotic and biotic stimuli during active defense processes. The peptides display a broad spectrum of antimicrobial activities. Their potent anti-pathogenic characteristics have ensured that they are promising targets in the medical and agricultural biotechnology sectors.

RESULTS

A berry specific cDNA sequence designated Vv-AMP1, Vitis vinifera antimicrobial peptide 1, was isolated from Vitis vinifera. Vv-AMP1 encodes for a 77 amino acid peptide that shows sequence homology to the family of plant defensins. Vv-AMP1 is expressed in a tissue specific, developmentally regulated manner, being only expressed in berry tissue at the onset of berry ripening and onwards. Treatment of leaf and berry tissue with biotic or abiotic factors did not lead to increased expression of Vv-AMP1 under the conditions tested. The predicted signal peptide of Vv-AMP1, fused to the green fluorescent protein (GFP), showed that the signal peptide allowed accumulation of its product in the apoplast. Vv-AMP1 peptide, produced in Escherichia coli, had a molecular mass of 5.495 kDa as determined by mass spectrometry. Recombinant Vv-AMP1 was extremely heat-stable and showed strong antifungal activity against a broad spectrum of plant pathogenic fungi, with very high levels of activity against the wilting disease causing pathogens Fusarium oxysporum and Verticillium dahliae. The Vv-AMP1 peptide did not induce morphological changes on the treated fungal hyphae, but instead strongly inhibited hyphal elongation. A propidium iodide uptake assay suggested that the inhibitory activity of Vv-AMP1 might be associated with altering the membrane permeability of the fungal membranes.

CONCLUSION

A berry specific cDNA clone, Vv-AMP1, was isolated and characterized and shown to encode a plant defensin. Recombinant Vv-AMP1 displayed non-morphogenic antifungal activity against a broad spectrum of fungi, probably altering the membrane permeability of the fungal pathogens. The expression of this peptide is highly regulated in Vitis vinifera, hinting at an important defense role during berry-ripening.

Seed defensins of barnyard grass Echinochloa crusgalli (L.) Beauv

From the annual weed barnyard grass Echinochloa crusgalli (L.) Beauv., two novel defensins Ec-AMP-D1 and Ec-AMP-D2 that differ by a single amino acid substitution were isolated by a combination of different chromatographic procedures. Both defensins were active against several phytopathogenic fungi and the oomycete Phytophthora infestans at micromolar concentrations. The Ec-AMP-D1 showed higher activity against the oomycete than Ec-AMP-D2. The comparison of the amino acid sequences of the antifungal E. crusgalli defensins with those of earlier characterized T. kiharae defensins [T.I. Odintsova, Ts.A. Egorov, A.Kh. Musolyamov, M.S. Odintsova, V.A. Pukhalsky, E.V. Grishin, Seed defensins from T. kiharae and related species: genome localization of defensin-encoding genes, Biochimie, 89 (2007) 605-612.] that were devoid of substantial antifungal activity point to the C-terminal region of the molecule as the main determinant of the antifungal activity of E. crusgalli defensins.

Analysis of Triticum boeoticum and Triticum urartu seed defensins: To the problem of the origin of polyploid wheat genomes

The origin of polyploid wheat genomes has been the subject of numerous studies and is the key problem in wheat phylogeny. Different diploid species have been supposed to donate genomes to tetraploid and hexaploid wheat species. To shed light on phylogenetic relationships between the presumable A genome donors and hexaploid wheat species we have applied a new approach: the comparison of defensins from diploid Triticum species, Triticum boeoticum Boiss. and Triticum urartu Thum. ex Gandil., with previously characterized Triticum kiharae defensins [T.I. Odintsova et al., Biochimie 89 (2007) 605-612]. Defensins were isolated by acidic extraction of seeds followed by three-step chromatographic separation. Isolated defensins were identified by molecular masses using MALDI-TOF mass spectrometry and N-terminal sequencing. For the first time, we have shown that T. urartu defensins are more similar to those of the hexaploid wheat than T. boeoticum defensins, although variation among samples collected in different regions of the world was revealed. Our results clearly demonstrate that T. urartu of the Asian origin contributed the A genome to polyploid wheat species.

The antifungal activity of RsAFP2, a plant defensin from raphanus sativus, involves the induction of reactive oxygen species in Candida albicans

RsAFP2 (Raphanus sativus antifungal peptide 2), an antifungal plant defensin isolated from seed of R. sativus, interacts with glucosylceramides (GlcCer) in membranes of susceptible yeast and fungi and induces membrane permeabilization and fungal cell death. However, using carboxyfluorescein-containing small unilamellar vesicles containing purified GlcCer, we could not observe permeabilization as a consequence of insertion of RsAFP2 in such vesicles. Therefore, we focused on a putative RsAFP2-induced signaling cascade downstream of RsAFP2-binding to GlcCer in fungal membranes. We show that RsAFP2 induces reactive oxygen species (ROS) in Candida albicans wild type in a dose-dependent manner, but not at all in an RsAFP2-resistant DeltagcsC. albicans mutant that lacks the RsAFP2-binding site in its membranes. These findings indicate that upstream binding of RsAFP2 to GlcCer is needed for ROS production leading to yeast cell death. Moreover, the antioxidant ascorbic acid blocks RsAFP2-induced ROS generation, as well as RsAFP2 antifungal activity. These data point to the presence of an intracellular plant defensin-induced signaling cascade, which involves ROS generation and leads to fungal cell growth arrest.

X-tox: an atypical defensin derived family of immune-related proteins specific to Lepidoptera

We report here the isolation in Spodoptera frugiperda (Lepidoptera) of an immune-related protein (hereafter named Spod-11-tox), characterized by imperfectly conserved tandem repeats of 11 cysteine-stabilized alpha beta motifs (CS-alphabeta), the structural scaffold characteristic of invertebrate defensins and scorpion toxins. Spod-11-tox orthologs were only found in Lepidopteran species, suggesting that this new protein family (named X-tox) is specific to this insect order. Moreover, phylogenetic analysis suggests that X-tox proteins represent a new class of proteins restricted to Lepidoptera and likely derived from Lepidopteran defensins. In S. frugiperda, analysis of gene expression revealed that spod-11-tox is rapidly induced by infection. However, and conversely to what is known for most insect antimicrobial peptides (AMP), spod-11-tox is mainly expressed in blood cells. Moreover, recombinant Spod-11-tox produced in the Sf9 cell line does not show any antimicrobial activity. Altogether, these results suggest that although X-tox proteins are derived from defensins, they may play a different and still unknown role in Lepidoptera immune response.

Analysis of the immune-inducible transcriptome from microbial stress resistant, rat-tailed maggots of the drone fly Eristalis tenax

Background

The saprophagous and coprophagous maggots of the drone fly Eristalis tenax (Insecta, Diptera) have evolved the unique ability to survive in aquatic habitats with extreme microbial stress such as drains, sewage pools, and farmyard liquid manure storage pits. Therefore, they represent suitable models for the investigation of trade-offs between the benefits resulting from colonization of habitats lacking predators, parasitoids, or competitors and the investment in immunity against microbial stress. In this study, we screened for genes in E. tenax that are induced upon septic injury. Suppression subtractive hybridization was performed to selectively amplify and identify cDNAs that are differentially expressed in response to injected crude bacterial endotoxin (LPS).

Results

Untreated E. tenax maggots exhibit significant antibacterial activity in the hemolymph which strongly increases upon challenge with LPS. In order to identify effector molecules contributing to this microbial defense we constructed a subtractive cDNA library using RNA samples from untreated and LPS injected maggots. Analysis of 288 cDNAs revealed induced expression of 117 cDNAs corresponding to 30 novel gene clusters in E. tenax. Among these immune-inducible transcripts we found homologues of known genes from other Diptera such as Drosophila and Anopheles that mediate pathogen recognition (e.g. peptidoglycan recognition protein) or immune-related signaling (e.g. relish). As predicted, we determined a high diversity of novel putative antimicrobial peptides including one E. tenax defensin.

Conclusion

We identified 30 novel genes of E. tenax that were induced in response to septic injury including novel putative antimicrobial peptides. Further analysis of these immune-related effector molecules from Eristalis may help to elucidate the interdependency of ecological adaptation and molecular evolution of the innate immunity in Diptera.

Structure-based protein engineering for alpha-amylase inhibitory activity of plant defensin

The structure of a novel plant defensin isolated from the seeds of the mung bean, Vigna radiate, has been determined by (1)H nuclear magnetic resonance spectroscopy. The three-dimensional structure of VrD2, the V. radiate plant defensin 2 protein, comprises an alpha-helix and one triple-stranded anti-parallel beta-sheet stabilized by four disulfide bonds. This protein exhibits neither insecticidal activity nor alpha-amylase inhibitory activity in spite of showing a similar global fold to that of VrD1, an insecticidal plant defensin that has been suggested to function by inhibiting insect alpha-amylase. Our previous study proposed that loop L3 of plant defensins is important for this inhibition. Structural analyses and surface charge comparisons of VrD1 and VrD2 revealed that the charged residues of L3 correlate with the observed difference in inhibitory activities of these proteins. A VrD2 chimera that was produced by transferring the proposed functional loop of VrD1 onto the structurally equivalent loop of VrD2 supported this hypothesis. The VrD2 chimera, which differs by only five residues compared with VrD2, showed obvious activity against Tenebrio molitor alpha-amylase. These results clarify the mode of alpha-amylase inhibition of plant defensins and also represent a possible approach for engineering novel alpha-amylase inhibitors. Plant defensins are important constituents of the innate immune system of plants, and thus the application of protein engineering to this protein family may provide an efficient method for protecting against crop losses.

Sequence characterization and expression patterns of two defensin-like antimicrobial peptides from the tick Haemaphysalis longicornis

Two cDNAs encoding defensin-like antimicrobial peptides were cloned and sequenced from the tick Haemaphysalis longicornis. The full-length cDNA of Hlgut-defensin (H. longicornis midgut defensin) is 333bp, encoding an expected protein with 73 amino acids. The full-length cDNA of Hlsal-defensin (H. longicornis salivary gland defensin) is 382bp, encoding an expected protein with 81 amino acids. The antibacterial activities of the synthetic peptides based on the Hlgut-defensin and Hlsal-defensin sequences were tested against a variety of Gram-positive and Gram-negative bacteria. Using real-time PCR, the tissue-specific expression of two defensin-like peptides were determined and it was also found that the gene transcripts of Hlgut-defensin and Hlsal-defensin were significantly induced by a lipopolysaccharide (LPS) injection.

Purification and characterization of eight peptides from Galleria mellonella immune hemolymph

Defense peptides play a crucial role in insect innate immunity against invading pathogens. From the hemolymph of immune-challenged greater wax moth, Galleria mellonella (Gm) larvae, eight peptides were isolated and characterized. Purified Gm peptides differ considerably in amino acid sequences, isoelectric point values and antimicrobial activity spectrum. Five of them, Gm proline-rich peptide 2, Gm defensin-like peptide, Gm anionic peptides 1 and 2 and Gm apolipophoricin, were not described earlier in G. mellonella. Three others, Gm proline-rich peptide 1, Gm cecropin D-like peptide and Galleria defensin, were identical with known G. mellonella peptides. Gm proline-rich peptides 1 and 2 and Gm anionic peptide 2, had unique amino acid sequences and no homologs have been found for these peptides. Antimicrobial activity of purified peptides was tested against gram-negative and gram-positive bacteria, yeast and filamentous fungi. The most effective was Gm defensin-like peptide which inhibited fungal and sensitive bacteria growth in a concentration of 2.9 and 1.9 microM, respectively. This is the first report describing at least a part of defense peptide repertoire of G. mellonella immune hemolymph.

New tick defensin isoform and antimicrobial gene expression in response to Rickettsia montanensis challenge

Recent studies aimed at elucidating the rickettsia-tick interaction have discovered that the spotted fever group rickettsia Rickettsia montanensis, a relative of R. rickettsii, the etiologic agent of Rocky Mountain spotted fever, induces differential gene expression patterns in the ovaries of the hard tick Dermacentor variabilis. Here we describe a new defensin isoform, defensin-2, and the expression patterns of genes for three antimicrobials, defensin-1 (vsnA1), defensin-2, and lysozyme, in the midguts and fat bodies of D. variabilis ticks that were challenged with R. montanensis. Bioinformatic and phylogenetic analyses of the primary structure of defensin-2 support its role as an antimicrobial. The tissue distributions of the three antimicrobials, especially the two D. variabilis defensin isoforms, are markedly different, illustrating the immunocompetence of the many tissues that R. montanensis presumably invades once acquired by the tick. Antimicrobial gene expression patterns in R. montanensis-challenged ticks suggest that antimicrobial genes play a role during the acquisition-invasion stages in the tick.

A mitogenic defensin from white cloud beans (Phaseolus vulgaris)

A peptide, with a molecular mass of 7458 Da, was purified from the seeds of white cloud beans (Phaseolus vulgaris cv. 'white cloud bean'). This peptide was isolated using a simple protocol consisting of affinity chromatography on Affi-gel blue gel and gel filtration on Superdex 75. The peptide had both antifungal and antibacterial activities. It reduced the activity of HIV-1 reverse transcriptase and it also inhibited translation in a cell-free rabbit reticulocyte lysate system. Its antifungal activity was retained after incubation with trypsin but was reduced when the ambient ionic strength was raised. The peptide elicited a mitogenic response from mouse splenocytes but did not stimulate nitric oxide production in mouse macrophages.

Limenin, a defensin-like peptide with multiple exploitable activities from shelf beans

From the seeds of the shelf bean, an antifungal peptide with a molecular mass of 6.5 kDa was isolated. The isolation procedure comprised affinity chromatography on Affi-gel blue gel, ion exchange chromatography on Mono S, and gel filtration on Superdex 75. The peptide was adsorbed on Affi-gel blue gel and Mono S. It potently suppressed mycelial growth in Botrytis cinerea, Fusarium oxysporum, and Mycosphaerella arachidicola with an IC(50) of 2.9, 2.1, and 0.34 microM, respectively. It exerted antibacterial activity toward several bacterial species with an IC(50) approximating 100 microM. [Methyl-(3)H]-thymidine incorporation into isolated mouse splenocytes was stimulated. [Methyl-(3)H]-thymidine incorporation into M1 (myeloma) and L1210 (leukemia) cells was inhibited. The peptide reduced the activity of HIV-1 reverse transcriptase and also inhibited translation in a cell-free rabbit reticulocyte lysate system.

Purification of a novel arthropod defensin from the American oyster, Crassostrea virginica

An antimicrobial peptide was purified from acidified gill extract of a bivalve mollusk, the American oyster (Crassostrea virginica), by preparative acid-urea--polyacrylamide gel electrophoresis and reversed-phase high performance liquid chromatography. The 4265.0 Da peptide had 38 amino acids, including 6 cysteines. It showed strongest activity against Gram-positive bacteria (Lactococcus lactis subsp. lactis and Staphylococcus aureus; minimum effective concentrations [MECs] 2.4 and 3.0 microg/ml, respectively) but also had significant activity against Gram-negative bacteria (Escherichia coli D31 and Vibrio parahemolyticus; MECs 7.6 and 15.0 microg/ml, respectively). Comparison of the amino acid sequence with those of other known antimicrobial peptides revealed that the novel peptide had high sequence homology to arthropod defensins, including those from other bivalves, the mussels Mytilus edulis and Mytilus galloprovincialis. This is the first antimicrobial peptide to be isolated from any oyster species and we have named it American oyster defensin (AOD).

Analysis of urinary calculi obtained from a patient with idiopathic hypouricemia using micro area x-ray diffractometry and LC-MS

Urolithiasis is a common complication in patients with hypouricemia. Using a microarea x-ray diffractometer and nanoflow liquid chromatography-mass spectrometry (LC-MS) following SDS-polyacrylamide gel electrophoresis (PAGE), recurrent urinary calculi complicating a hypouricemic patient were analyzed. Analysis with the microarea x-ray diffractometer showed that one of the calculi was composed of calcium oxalate monohydrate and hydroxyapatite. The other was found to be formed from calcium oxalate dihydrate. After determination with LC-MS, both were found to contain uromodulin, albumin, osteopontin, protein Z, and defensins. Lysozyme and calgranulin A were also identified in these calculi. Defensins, which were antimicrobial peptides, and lysozyme, a mucopeptide glycohydrolase, were identified as new organic components of urinary stones. The role of these proteins in the process of urolithiasis is of particular interest.

Sesquin, a potent defensin-like antimicrobial peptide from ground beans with inhibitory activities toward tumor cells and HIV-1 reverse transcriptase

An antifungal peptide with a molecular mass around 7 kDa and an N-terminal sequence highly homologous to defensin was isolated from ground beans (Vigna sesquipedalis cv. 'Ground Bean'). The peptide was adsorbed on Affi-gel blue gel and on Mono S. It exerted an antifungal action on Botrytis cinerea, Fusarium oxysporum and Mycosphaerella arachidicola; and an antibacterial action on Escherichia coli B, Proteus vulgaris, Mycobacterium phlei and Bacillus megaterium. The antimicrobial activity was inhibited in presence of the 5 mM CaCl2 and MgCl2, but no inhibition was observed in 5 mM NaCl. The peptide exerted antiproliferative activity toward breast cancer (MCF-7) cells and leukemia M1 cells, this activity could not be inhibited by the ions mentioned above. It also exhibited some inhibitory activity toward human immunodeficiency virus-type 1 reverse transcriptase.

Prodefensins are matrix proteins of specific granules in human neutrophils

Defensins are potent antimicrobial and proinflammatory peptides. The human neutrophil defensins human neutrophil peptide (HNP)-1-3 are synthesized as 94 amino acide (aa) preproHNPs, which are converted to 75 aa proHNPs by cotranslational removal of a 19 aa endoplasmic reticulum signal peptide. At the promyelocytic stage of myelopoiesis, proHNPs are further proteolytically modified and accumulate in azurophil granules as 29-30 aa HNPs. In contrast, proHNPs produced by more mature myeloid cells are not subjected to proteolytic cleavage and undergo a high degree of constitutive exocytosis. The proHNPs are devoid of antimicrobial potential, and the significance of their secretion is unknown. To investigate whether mature neutrophils contain proHNPs, we developed antibodies against proHNP-1 by DNA immunization of rabbits. In addition, antibodies against the 45 aa proHNP pro-piece were raised by conventional immunization procedures. These antibodies allowed detection of proHNPs in homogenates of peripheral blood neutrophils. The proHNPs were isolated by affinity chromatography, and their identity was confirmed by mass spectrometry and N-terminal aa sequence analysis. Finally, the neutrophil proHNPs were identified as novel matrix proteins of specific granules by subcellular fractionation experiments, release studies, and immunoelectron microscopy. Thus, human neutrophils not only store large amounts of mature defensins in azurophil granules but also contain a more easily mobilized reservoir of unprocessed prodefensins in specific granules.

Phaseococcin, an antifungal protein with antiproliferative and anti-HIV-1 reverse transcriptase activities from small scarlet runner beans

From the seeds of small scarlet runner beans (Phaseolus coccineus 'Minor'), an antifungal protein with an N-terminal sequence homologous to those of defensins was isolated. The antifungal protein bound to Affi-gel blue gel and Mono S but it did not bind to DEAE-cellulose. It was further purified by gel filtration on a Superdex peptide column. It exhibited a molecular mass of 5422 Da as determined by mass spectrometry. The protein, designated as phaseococcin, suppressed mycelial growth in a number of fungi including Botrytis cinerea, Coprinus comatus, Fusarium oxysporum, Mycosphaerella arachidicola, Physalospora piricola, and Rhizoctonia solani. It also inhibited proliferation in several Bacillus species and the leukemia cell lines HL60 and L1210 and curtailed the activity of HIV-1 reverse transcriptase. It did not affect proliferation of mouse splenocytes and neither did it inhibit protein synthesis in a cell-free rabbit reticulocyte lysate system.Key words: antifungal proteins, runner beans, antiproliferative.

Purification, characterization, and sequencing of novel antimicrobial peptides, Tu-AMP 1 and Tu-AMP 2, from bulbs of tulip (Tulipa gesneriana L.)

Novel antimicrobial peptides (AMP), designated Tu-AMP 1 and Tu-AMP 2, were purified from the bulbs of tulip (Tulipa gesneriana L.) by chitin affinity chromatography and reverse-phase high-performance liquid chromatography (HPLC). They bind to chitin in a reversible way. They were basic peptides having isoelectric points of over 12. Tu-AMP 1 and Tu-AMP 2 had molecular masses of 4,988 Da and 5,006 Da on MALDI-TOF MS analysis, and their extinction coefficients of 1% aqueous solutions at 280 nm were 3.3 and 3.4, respectively. Half of all amino acid residues of Tu-AMP 1 and Tu-AMP 2 were occupied by cysteine, arginine, lysine, and proline. The concentrations of peptides required for 50% inhibition (IC(50)) of the growth of plant pathogenic bacteria and fungi were 2 to 20 microg/ml. The structural characteristics of Tu-AMP 1 and Tu-AMP 2 indicated that they were novel thionin-like antimicrobial peptides, though Tu-AMP 2 was a heterodimer composes of two short peptides joined with disulfide bonds.

Two novel non-cationic defensin-like antimicrobial peptides from haemolymph of the female tick, Amblyomma hebraeum

Two non-cationic defensin-like antimicrobial peptides, named Amblyomma defensin peptide 1 and Amblyomma defensin peptide 2, were identified from the hard tick, Amblyomma hebraeum, by a combination of suppression subtractive hybridization for differentially expressed genes and proteomics. cDNA clones encoding each of these two defensin-like antimicrobial peptides were isolated from the differentially expressed cDNA library of the tick synganglia (central nervous system). The preproproteins deduced from the cDNA sequences each have 92 amino acid residues. Amblyomma defensin peptide 2 was purified from the haemolymph of fed female ticks. The purified peptide displayed antibacterial activity against Gram-negative and Gram-positive bacteria. Amblyomma defensin peptide 1 was further identified by protein chip capture combined with SELDI-TOF (surface-enhanced laser desorption/ionization-time-of-flight) MS. By screening for differentially expressed proteins, it was found that the expression of Amblyomma defensin peptide 1 was upregulated during 4 days post-feeding. Our findings firstly provide two defensin-like antimicrobial peptides that are particularly novel in being anionic, together with corresponding cDNA sequences, in hard ticks, and prove that the combination of suppression subtractive hybridization and protein profiling is a powerful method to study differentially expressed proteins, especially for organisms without available genome sequence information.

Purification, cDNA cloning and expression of an insect defensin from the great wax moth, Galleria mellonella

An insect defensin, named Galleria defensin, was purified from the larval haemolymph of Galleria mellonella immunized against E. coli. The peptide was composed of forty-three amino acid residues containing six cysteines that might be engaged in intramolecular disulphide bridges. The primary structure of Galleria defensin shared about 90.7% identity to that of heliomicin, which was an insect defensin isolated from Heliothis virescens. The full-length cDNA encoding Galleria defensin was cloned from the fat body of the immunized G. mellonella larvae. Northern blot analysis revealed that Galleria defensin was expressed not only in the fat body but also in the midgut against invading bacteria into haemocoel. This is the first report presenting cDNA and expression of an insect defensin in the lepidopteran species.

[Purification of a big defensin from Ruditapes philippinesis and its antibacterial activity]

A novel big defensin was isolated and characterized from the plasma of Ruditapes philippinesis. It was purified to homogeneity by means of precipitation with (NH(4))(2)SO(4), gel-exclusion chromatography, two kinds of cation-exchange chromatography and named RPD-1. Its relative molecular mass was 24.8 kD by means of SDS-PAGE. By means of ABI437 amino acid sequence analyser, its 11 NH(2)-terminal amino acid sequence is AVPDVAFNAYG. Two databank systems (NCBI and EBI/EMBL) was indexed, no sequence with homology to RPD-1 was found. Furthermore, it exhibited strong inhibition on the growth of Gram-negative and -positive bacteria. Minimal inhibitory concentration (MIC) of RPD-1 against Staphylococcus aureus, Bacillus subtilis, Micrococcus tetragenus, Escherichia coli, Vibrio parahaemolyticus, Vibrio anguillarum was 9.6 mg/L, 76.8 mg/L, 38.4 mg/L, 76.8 mg/L, 19.2 mg/L, 19.2 mg/L respectively.

Minidefensins: antimicrobial peptides with activity against HIV-1

Over 80 different alpha-defensin or beta-defensin peptides are expressed by the leukocytes and epithelial cells of birds and mammals. Although their broad spectrum antimicrobial properties makes them candidates for therapeutic development, technical limitations related to their size (typically 30-45 residues) and complex structure have impeded such development. The minidefensins covered in this review are antimicrobial peptides with 16-18 residues, approximately half the number found in alpha-defensins. The theta-defensins are evolutionarily related toalpha- and beta-defensins, but other minidefensins probably arose independently. Like alpha- or beta-defensins, minidefensin molecules have a net positive charge and a largely beta-sheet structure that is stabilized by intramolecular disulfide bonds. Whereas alpha-defensins are found only in mammals and theta-defensins only in nonhuman primates, the other minidefensins come from widely divergent species, including horseshoe crabs, spiders, and pigs. Several alpha-defensins and minidefensins are effective inhibitors of HIV-1 infection in vitro, and recent evidence implicates alpha-defensins in resistance to HIV-1 progression in vivo. This review compares defensins and minidefensins with respect to their activity against HIV-1. It pays special attention to retrocyclins - the ancestral theta-defensins of humans, and their extant counterparts in rhesus monkeys. In addition to describing critical elements of their structure and unusual mode of formation, we will venture some predictions about using theta-defensins as antiviral agents.

Purification, characterization, and sequencing of a novel type of antimicrobial peptides, Fa-AMP1 and Fa-AMP2, from seeds of buckwheat (Fagopyrum esculentum Moench.)

Novel antimicrobial peptides (AMP), designated Fa-AMP1 and Fa-AMP2, were purified from the seeds of buckwheat (Fagopyrum esculentum Moench.) by gel filtration on Sephadex G75, ion-exchange HPLC on SP COSMOGEL, and reverse-phase HPLC. They were basic peptides having isoelectric points of over 10. Fa-AMP1 and Fa-AMP2 had molecular masses of 3,879 Da and 3,906 Da on MALDI-TOF MS analysis, and their extinction coefficients in 1% aqueous solutions at 280 nm were 42.8 and 38.9, respectively. Half of all amino acid residues of Fa-AMP1 and Fa-AMP2 were cysteine and glycine, and they had continuous sequences of cysteine and glycine. The concentrations of peptides required for 50% inhibition (IC50) of the growth of plant pathogenic fungi, and Gram-positive and -negative bacteria were 11 to 36 microg/ml. The structural and antimicrobial characteristics of Fa-AMPs indicated that they are a novel type of antimicrobial peptides belonging to a plant defensin family.