In vitro antimicrobial properties of recombinant ASABF, an antimicrobial peptide isolated from the nematode Ascaris suum

Helminthic host defense peptides: using the parasite to defend the host

Parasitic helminths are destined to share niches with a variety of microbiota that inevitably influence their interaction with the host. To modulate the microbiome for their benefit and defend against pathogenic isolates, helminths have developed host defense peptides (HDPs) and proteins as integral elements of their immunity. These often exert a relatively nonspecific membranolytic activity toward bacteria, sometimes with limited or no toxicity toward host cells. With a few exceptions, such as nematode cecropin-like peptides and antibacterial factors (ABFs), helminthic HDPs are largely underexplored. This review scrutinizes current knowledge on the repertoire of such peptides in helminths and promotes their research as potential leads for an anti-infective solution to the burgeoning problem of antibiotic resistance.

In vitro and in vivo efficacy of Caenorhabditis elegans recombinant antimicrobial protein against Gram-negative bacteria

Antimicrobial peptides (AMPs) are short, positively charged host defense peptides, found in various life forms from microorganisms to humans. AMPs are gaining more attention as substitutes for antibiotics in order to combat the risk posed by multi-drug- resistant pathogens. The nematode Caenorhabditis elegans relies solely on its innate immune defense to cope with its challenging life-style. Bacterial infection in C. elegans leads to induction of antimicrobial proteins, defensins, nemapores, cecropins, and neuropeptide-like proteins, which act to limit bacterial proliferation. This study reports how the C. elegans recombinant antibacterial factor (ABF-1) rapidly inhibited bacterial growth (Salmonella Typhi, Klebsiella pneumonia, Shigella sonnei and Vibrio alginolyticus). The ABF-1 exposure on S. Typhi, showed differential regulation in cell-cycle, DNA repair mechanism, membrane stability, and stress related proteins. The exogenous supply of ABF-1 protein has extended C. elegans survival by reducing the bacterial colony forming units on the nematode intestine. Together, these findings indicate the valuable and potential therapeutic applications of ABF-1 protein as antimicrobial agents against intracellular pathogens.

Worms' Antimicrobial Peptides

Antimicrobial peptides (AMPs) are natural antibiotics produced by all living organisms. In metazoans, they act as host defense factors by eliminating microbial pathogens. But they also help to select the colonizing bacterial symbionts while coping with specific environmental challenges. Although many AMPs share common structural characteristics, for example having an overall size between 10-100 amino acids, a net positive charge, a γ-core motif, or a high content of cysteines, they greatly differ in coding sequences as a consequence of multiple parallel evolution in the face of pathogens. The majority of AMPs is specific of certain taxa or even typifying species. This is especially the case of annelids (ringed worms). Even in regions with extreme environmental conditions (polar, hydrothermal, abyssal, polluted, etc.), worms have colonized all habitats on Earth and dominated in biomass most of them while co-occurring with a large number and variety of bacteria. This review surveys the different structures and functions of AMPs that have been so far encountered in annelids and nematodes. It highlights the wide diversity of AMP primary structures and their originality that presumably mimics the highly diverse life styles and ecology of worms. From the unique system that represents marine annelids, we have studied the effect of abiotic pressures on the selection of AMPs and demonstrated the promising sources of antibiotics that they could constitute.

Reciprocal Interactions between Nematodes and Their Microbial Environments

Parasitic nematode infections are widespread in nature, affecting humans as well as wild, companion, and livestock animals. Most parasitic nematodes inhabit the intestines of their hosts living in close contact with the intestinal microbiota. Many species also have tissue migratory life stages in the absence of severe systemic inflammation of the host. Despite the close coexistence of helminths with numerous microbes, little is known concerning these interactions. While the environmental niche is considerably different, the free-living nematode Caenorhabditis elegans (C. elegans) is also found amongst a diverse microbiota, albeit on decaying organic matter. As a very well characterized model organism that has been intensively studied for several decades, C. elegans interactions with bacteria are much more deeply understood than those of their parasitic counterparts. The enormous breadth of understanding achieved by the C. elegans research community continues to inform many aspects of nematode parasitology. Here, we summarize what is known regarding parasitic nematode-bacterial interactions while comparing and contrasting this with information from work in C. elegans. This review highlights findings concerning responses to bacterial stimuli, antimicrobial peptides, and the reciprocal influences between nematodes and their environmental bacteria. Furthermore, the microbiota of nematodes as well as alterations in the intestinal microbiota of mammalian hosts by helminth infections are discussed.

Overexpression of an antimicrobial peptide derived from C. elegans using an aggregation-prone protein coexpression system

Antibacterial factor 2 (ABF-2) is a 67-residue antimicrobial peptide derived from the nematode Caenorhabditis elegans. Although it has been reported that ABF-2 exerts in vitro microbicidal activity against a range of bacteria and fungi, the structure of ABF-2 has not yet been solved. To enable structural studies of ABF-2 by NMR spectroscopy, a large amount of isotopically labeled ABF-2 is essential. However, the direct expression of ABF-2 in Escherichia coli is difficult to achieve due to its instability. Therefore, we applied a coexpression method to the production of ABF-2 in order to enhance the inclusion body formation of ABF-2. The inclusion body formation of ABF-2 was vastly enhanced by coexpression of aggregation-prone proteins (partner proteins). By using this method, we succeeded in obtaining milligram quantities of active, correctly folded ABF-2. In addition, ¹⁵ N-labeled ABF-2 and a well-dispersed heteronuclear single quantum coherence (HSQC) spectrum were also obtained successfully. Moreover, the effect of the charge of the partner protein on the inclusion body formation of ABF-2 in this method was investigated by using four structurally homologous proteins. We concluded that a partner protein of opposite charge enhanced the formation of an inclusion body of the target peptide efficiently.

Expression and characterization of recombinant bovine lactoferrin in E. coli

Lactoferrin is a member of the transferrin family of iron-binding proteins with a number of properties, including antibacterial activity against a broad spectrum of Gram-negative and Gram-positive bacteria. bovine lactoferrin cDNA was isolated, cloned and expressed as a fusion protein. The amino acid sequence of the fusion was analyzed and compared with other species. Crystallographic data were used to compare structural differences between bovine and human lactoferrin in 3-D models. A thioredoxin fusion protein was expressed and shown to have a different molecular weight compared with native bLf. After purification using Ni-NTA, the yield of recombinant bovine lactoferrin was 15.3 mg/l with a purity of 90.3 %. Recombinant bLf and pepsin-digested rbLf peptides demonstrated antibacterial activity of 79.8 and 86.9 %, respectively. The successful expression of functional, active and intact rbLf allows us to study the biochemical interactions of antimicrobial proteins and peptides and will facilitate their study as immunomodulators.

Distribution and characteristics of ABFs, cecropins, nemapores, and lysozymes in nematodes

Several groups of antimicrobial effector molecules have been identified in nematodes, but most studies have been limited to Caenorhabditis elegans and, to a lesser extent, Ascaris suum. Although these two species are not closely related, they are not representative of overall nematode diversity. This study utilized available sequence information to investigate whether four groups of antimicrobial effectors (defensin-like antibacterial factors [ABFs], cecropins, saposin domain-containing proteins, and lysozymes) are components of an archetypal nematode immune system or more narrowly restricted. Saposin domain-containing proteins (caenopores in C. elegans) and lysozymes were widely distributed and found in most taxa, but likely have digestive as well as defensive functions. ABFs were widely distributed in fewer taxa, suggesting selective loss in some lineages. In contrast, cecropins were identified in only three related species, suggesting acquisition of this effector molecule in their common ancestor.

Inducible ASABF-type antimicrobial peptide from the sponge Suberites domuncula: microbicidal and hemolytic activity in vitro and toxic effect on molluscs in vivo

Since sponges, as typical filter-feeders, are exposed to a high load of attacking prokaryotic and eukaryotic organisms, they are armed with a wide arsenal of antimicrobial/cytostatic low-molecular-weight, non-proteinaceous bioactive compounds. Here we present the first sponge agent belonging to the group of ASABF-type antimicrobial peptides. The ASABF gene was identified and cloned from the demosponge Suberites domuncula. The mature peptide, with a length of 64 aa residues has a predicted pI of 9.24, and comprises the characteristic CSα β structural motif. Consequently, the S. domuncula ASABF shares high similarity with the nematode ASABFs; it is distantly related to the defensins. The recombinant peptide was found to display besides microbicidal activity, anti-fungal activity. In addition, the peptide lyses human erythrocytes. The expression of ASABF is upregulated after exposure to the apoptosis-inducing agent 2,2′-dipyridyl. During the process of apoptosis of surface tissue of S. domuncula, grazing gastropods (Bittium sp.) are attracted by quinolinic acid which is synthesized through the kynurenine pathway by the enzyme 3-hydroxyanthranilate 3,4-dioxygenase (HAD). Finally, the gastropods are repelled from the sponge tissue by the ASABF. It is shown that the effector peptide ASABF is sequentially expressed after the induction of the HAD gene and a caspase, as a central enzyme executing apoptosis.

C. elegans: model host and tool for antimicrobial drug discovery

For almost four decades, the nematode Caenorhabditis elegans has been of great value in many fields of biological research. It is now used extensively in studies of microbial pathogenesis and innate immunity. The worm lacks an adaptive immune system and relies solely on its innate immune defences to cope with pathogen attack. Infectious microbes, many of which are of clinical interest, trigger specific mechanisms of innate immunity, and provoke the expression of antifungal or antibacterial polypeptides. In this review, we highlight some of these families of antimicrobial peptides (AMPs) and proteins that are candidates for the development of novel antibiotics. In addition, we describe how systems of C. elegans infection provide an increasing number of possibilities for large-scale in vivo screens for the discovery of new antimicrobial drugs. These systems open promising perspectives for innovative human therapies.

Generation of novel cationic antimicrobial peptides from natural non-antimicrobial sequences by acid-amide substitution

Background

Cationic antimicrobial peptides (CAMPs) are well recognized to be promising as novel antimicrobial and antitumor agents. To obtain novel skeletons of CAMPs, we propose a simple strategy using acid-amide substitution (i.e. Glu→Gln, Asp→Asn) to confer net positive charge to natural non-antimicrobial sequences that have structures distinct from known CAMPs. The potential of this strategy was verified by a trial study.

Methods

The pro-regions of nematode cecropin P1-P3 (P1P-P3P) were selected as parent sequences. P1P-P3P and their acid-amide-substituted mutants (NP1P-NP3P) were chemically synthesized. Bactericidal and membrane-disruptive activities of these peptides were evaluated. Conformational changes were estimated from far-ultraviolet circular dichroism (CD) spectra.

Results

NP1P-NP3P acquired potent bactericidal activities via membrane-disruption although P1P-P3P were not antimicrobial. Far-ultraviolet CD spectra of NP1P-NP3P were similar to those of their parent peptides P1P-P3P, suggesting that NP1P-NP3P acquire microbicidal activity without remarkable conformational changes. NP1P-NP3P killed bacteria in almost parallel fashion with their membrane-disruptive activities, suggesting that the mode of action of those peptides was membrane-disruption. Interestingly, membrane-disruptive activity of NP1P-NP3P were highly diversified against acidic liposomes, indicating that the acid-amide-substituted nematode cecropin pro-region was expected to be a unique and promising skeleton for novel synthetic CAMPs with diversified membrane-discriminative properties.

Conclusions

The acid-amide substitution successfully generated some novel CAMPs in our trial study. These novel CAMPs were derived from natural non-antimicrobial sequences, and their sequences were completely distinct from any categories of known CAMPs, suggesting that such mutated natural sequences could be a promising source of novel skeletons of CAMPs.

An enhancer peptide for membrane-disrupting antimicrobial peptides

BACKGROUND

NP4P is a synthetic peptide derived from a natural, non-antimicrobial peptide fragment (pro-region of nematode cecropin P4) by substitution of all acidic amino acid residues with amides (i.e., Glu --> Gln, and Asp --> Asn).

RESULTS

In the presence of NP4P, some membrane-disrupting antimicrobial peptides (ASABF-alpha, polymyxin B, and nisin) killed microbes at lower concentration (e.g., 10 times lower minimum bactericidal concentration for ASABF-alpha against Staphylococcus aureus), whereas NP4P itself was not bactericidal and did not interfere with bacterial growth at

CONCLUSIONS

NP4P selectively enhanced the bactericidal activities of membrane-disrupting antimicrobial peptides by increasing the efficacy of membrane disruption against the cytoplasmic membrane.

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Key Words Collapse

MESH Headings

• Amino Acid Sequence
• Anti-Infective Agents/chemistry
• Anti-Infective Agents/pharmacology
• Antimicrobial Cationic Peptides/pharmacology
• Cell Membrane/drug effects
• Cell Membrane Permeability/drug effects
• Cell Proliferation/drug effects
• Drug Synergism
• Escherichia coli/drug effects
• Liposomes/metabolism
• Microbial Sensitivity Tests
• Molecular Sequence Data
• Peptides/chemistry
• Peptides/pharmacology
• Staphylococcus aureus/drug effects

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Affiliation(s)

Satoshi Ueno Division of Insect Sciences, National Institute of Agrobiological Sciences, Oowashi 1-2, Tsukuba, Ibaraki 305-8634, Japan Graduate School of Life and Environmental Sciences, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8572, Japan
Kohtaro Kusaka Division of Insect Sciences, National Institute of Agrobiological Sciences, Oowashi 1-2, Tsukuba, Ibaraki 305-8634, Japan
Yasushi Tamada Division of Insect Sciences, National Institute of Agrobiological Sciences, Oowashi 1-2, Tsukuba, Ibaraki 305-8634, Japan
Hong Zhang Division of Insect Sciences, National Institute of Agrobiological Sciences, Oowashi 1-2, Tsukuba, Ibaraki 305-8634, Japan
Masaomi Minaba Division of Insect Sciences, National Institute of Agrobiological Sciences, Oowashi 1-2, Tsukuba, Ibaraki 305-8634, Japan
Yusuke Kato Division of Insect Sciences, National Institute of Agrobiological Sciences, Oowashi 1-2, Tsukuba, Ibaraki 305-8634, Japan

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Evolution of ASABF (Ascaris suum antibacterial factor)-type antimicrobial peptides in nematodes: putative rearrangement of disulfide bonding patterns

ASABF (Ascaris suum antibacterial factor)-type antimicrobial peptides are defensin-like cysteine-rich peptides that are widely distributed in the phylum Nematoda. In known members of ASABF-type antimicrobial peptides, an array consisting of eight cysteine residues is completely conserved. In this study, we report a novel member ASABF-6Cys-alpha, which contains only six cysteine residues, in the pig round worm A. suum. The two cysteine residues deleted in ASABF-6Cys-alpha were not identical to a pair of half-cystine forming a disulfide bridge in ASABF-alpha, suggesting a rearrangement of disulfide bonding patterns. Gene organization and phylogenetic analyses suggested that ASABF-6Cys-alpha was generated from an ancestral ASABF gene after the divergence of Ascaridida from Rhabditida. ASABF-6Cys-alpha transcripts dramatically increased after bacterial injection, suggesting that ASABF-6Cys-alpha may contribute to immunity in nematodes.

Heterologous extracellular production of enterocin P fromEnterococcus faeciumP13 in the methylotrophic bacteriumMethylobacterium extorquens

Enterocin P (EntP), a strong antilisterial pediocin-like bacteriocin from Enterococcus faecium P13, was produced by Methylobacterium extorquens. For heterologous expression of EntP in the methylotrophic bacterium M. extorquens, a recombinant plasmid was constructed. The gene encoding the EntP structural gene (entP) was cloned into the plasmid vector pCM80, under control of the methanol dehydrogenase promoter (P(mxaF)), to generate plasmid pS25. When M. extorquens ATCC 55366 was transformed with pS25, EntP was detected and quantified in supernatants of the recombinant M. extorquens S25 strain by using specific anti-EntP antibodies and a non-competitive indirect enzyme-linked immunosorbent assay (NCI-ELISA). Purification of EntP by hydrophobic adsorption and reverse-phase (RP-FPLC) chromatographies, permitted recovery of active EntP from the supernatants of M. extorquens S25 grown in a synthetic defined medium.

Cecropin P1 and novel nematode cecropins: a bacteria-inducible antimicrobial peptide family in the nematode Ascaris suum

Cecropin P1 was first identified as a mammalian antimicrobial peptide isolated from the pig intestine. Much research aimed at characterizing this peptide has been reported. Recently, the workers who discovered the peptide corrected their original conclusion, and confirmed that this peptide originates in fact from the pig intestinal parasitic nematode, Ascaris suum. In the present study, we carried out a semi-exhaustive search for bacteria-inducible transcripts in A. suum by the cDNA subtraction method. The transcripts encoding cecropin P1 and novel Ascaris cecropins, designated cecropins P2, P3 and P4, were found to be positively induced factors. Chemically synthesized Ascaris cecropins were bactericidal against a wide range of microbes, i.e. Gram-positive (Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus) and Gram-negative (Pseudomonas aeruginosa, Salmonella typhimurium, Serratia marcescens and Esherichia coli) bacteria, and were weakly but detectably active against yeasts (Saccharomyces cerevisiae and Candida albicans). Cecropin P1-like sequences were also detected at least in two other species (Ascaris lumbricoides and Toxocara canis) of the Ascarididae. All Ascaris cecropin precursors contain an acidic pro-region connected by a tetra-basic cleavage site at the C-terminus. Such an acidic pro-region is also reported to be present in the tunicate cecropin-type antimicrobial peptide styelin. On the basis of the evolutionary position of nematodes and tunicates, the ancestral cecropin may have contained the acidic pro-region at the C-terminus.

Convergent evolution of invertebrate defensins and nematode antibacterial factors

Antibacterial factors (ABFs) are secreted polypeptides that have an important role in the innate immune system of nematodes. Comparison of these polypeptides revealed similarity in bioactivity, protein sequence and 3D structure, suggesting that they originated from a common ancestor. Comparison of gene organization of nematode ABF genes revealed that all except one contain a Phase 0 intron at a conserved location. The intron phase and location are congruent with the postulated intron gain rules, suggesting a gain of intron before duplication and divergence of the ancestral gene. Although nematode ABFs display similarity in activity and structure to invertebrate (arthropod and mollusk) defensins, lack of sequence similarity and the different genomic organization suggest that these two polypeptide families exhibit convergent evolution.

Production of enterocin P, an antilisterial pediocin-like bacteriocin from Enterococcus faecium P13, in Pichia pastoris

The gene encoding mature enterocin P (EntP), an antimicrobial peptide from Enterococcus faecium P13, was cloned into the pPICZalphaA expression vector to generate plasmid pJC31. This plasmid was integrated into the genome of P. pastoris X-33, and EntP was heterologously secreted from the recombinant P. pastoris X-33t1 derivative at a higher production and antagonistic activity than from E. faecium P13.

In vitro resistance to the CSαβ-type antimicrobial peptide ASABF-α is conferred by overexpression of sigma factor sigB in Staphylococcus aureus

OBJECTIVES

ASABF (Ascaris suum antibacterial factor) is a CSalphabeta-type antimicrobial peptide isolated from nematodes. ASABF-alpha, a member of ASABF, is particularly effective against the gram-positive pathogen Staphylococcus aureus. In this study, we investigated the role of sigB expression on ASABF-resistance in S. aureus.

METHODS

Based on preliminary characterization of the ASABF-resistant strain, Mu50, we speculated that the alternative sigma factor sigB may regulate resistance against antimicrobial peptides. To test this hypothesis, the ASABF susceptibility was compared between NKSB (a sigB-knockout derivative of N315) and its sigB-overexpressing derivative. In addition, similar experiments were carried out for N315ex, a deletion mutant of N315 for SCCmec (Staphylococcus cassette chromosome mec) which contains essential genes for beta-lactam resistance.

RESULTS

The sigB-overexpressing NKSB acquired an increased resistance to ASABF-alpha compared with the parent strain. The sigB-induced ASABF-alpha resistance was also observed in N315ex.

CONCLUSIONS

The overexpression of sigB confers resistance to the antimicrobial peptide, ASABF-alpha. SCCmec is not essential for this resistance.

Common structural properties specifically found in the CSalphabeta-type antimicrobial peptides in nematodes and mollusks: evidence for the same evolutionary origin?

The structural properties of the Ascaris suum antibacterial factor (ASABF)-type antimicrobial peptides, isolated from nematodes, were compared with the CSalphabeta-type antimicrobial peptides found in other organisms. The spacing of the half-cystine residues, cysteine pairings, and organization of the precursor were different from the 'classical' CSalphabeta-type antimicrobial peptides, such as drosomycin and plant defensins, and identical only to the MGD and myticin in mollusks. In addition, ABF-5, a member of the ASABF-type antimicrobial peptides in Caenorhabditis elegans, is predicted to contain a basic mature region and an acidic pro-region, similar to MGD and myticin. These results suggest that the ASABF-type antimicrobial peptides, MGD and myticin are similar in their structure.

Induction of ASABF (Ascaris suum antibacterial factor)-type antimicrobial peptides by bacterial injection: novel members of ASABF in the nematode Ascaris suum

Recently, invertebrate models have been widely used for the study of innate immunity. Nematodes are novel potential candidates because of the experimental advantages of Caenorhabditis elegans. However, whether nematodes have active immune responses is still ambiguous. Previously, we reported ASABF (Ascaris suum antibacterial factor)-type antimicrobial peptides in the parasitic nematode Ascaris suum and the genetic model nematode C. elegans. Further screening of a cDNA library and an expressed-sequence-tag database search detected five novel members of ASABF (ASABF-beta, -gamma, -delta, - epsilon and -zeta) in A. suum. The transcripts for ASABF-alpha, -beta, -gamma, and -delta clearly increased in the body wall, and also in the intestine for ASABF-delta, 4 h after injection of heat-killed bacteria into the pseudocoelom (body cavity), suggesting that these peptides are inducible in the acute phase of immune response. These results also suggest that the nematodes can recognize bacteria in the pseudocoelomic fluid and evoke an active immune response.

Tackling both sides of the host-pathogen equation with Caenorhabditis elegans

If one is interested in dissecting the complex interactions that exist between host and pathogen, the nematode worm Caenorhabditis elegans is perhaps not the first model host that comes to mind. In this review I will introduce 'the worm' and try to show how it is, in fact, well suited to the identification of universal virulence factors and holds great promise for the study of conserved mechanisms of innate immunity.

abf-1 and abf-2, ASABF-type antimicrobial peptide genes in Caenorhabditis elegans

Two genes encoding the ASABF (Ascaris suum antibacterial factor)-type antimicrobial peptide, abf-1 and abf-2, were identified in Caenorhabditis elegans. Recombinant ABF-2 exhibited potent microbicidal activity against Gram-positive and Gram-negative bacteria, and yeasts. The tissue-specific distribution estimated by immunofluorescence staining and transgenic analysis of a gfp fusion gene (where GFP corresponds to green fluorescent protein) suggested that ABF-2 contributes to surface defence in the pharynx. abf-1 contains a single intron at a conserved position, suggesting that asabf and abf originated from a common ancestor. Both transcripts for abf-1 and abf-2 were detected as two distinct forms, i.e. spliced leader (SL)1-trans-spliced with a long 5'-untranslated region (UTR) and SL-less with a short 5'-UTR. A polycistronic precursor RNA encoding ABF-1 and ABF-2 was detected, suggesting that these genes form an operon. An 'opportunistic operon' model for regulation of abf genes, including the generation of short SL-less transcripts, is proposed. In conclusion, C. elegans should have an immune defence system due to the antimicrobial peptides. C. elegans can be a novel model for innate immunity. Furthermore, the combination of biochemical identification in Ascaris suum and homologue hunting in C. elegans should be a powerful method of finding rapidly evolved proteins, such as some immune-related molecules in C. elegans.