Antimicrobial and cytolytic polypeptides of amoeboid protozoa--effector molecules of primitive phagocytes

Metabolic Regulation of Longevity and Immune Response in Caenorhabditis elegans by Ingestion of Lacticaseibacillus rhamnosus IDCC 3201 Using Multi-Omics Analysis

Probiotics, specifically Lacticaseibacillus rhamnosus, have garnered attention for their potential health benefits. This study focuses on evaluating the probiotic properties of candidate probiotics L. rhamnosus IDCC 3201 (3201) using the Caenorhabditis elegans surrogate animal model, a well-established in vivo system for studying host-bacteria interactions. The adhesive ability to the host's gastrointestinal tract is a crucial criterion for selecting potential probiotic bacteria. Our findings demonstrated that 3201 exhibits significantly higher adhesive capabilities compared with Escherichia coli OP50 (OP50), a standard laboratory food source for C. elegans and is comparable with the widely recognized probiotic L. rhamnosus GG (LGG). In lifespan assay, 3201 significantly increased the longevity of C. elegans compared with OP50. In addition, preconditioning with 3201 enhanced C. elegans immune response against four different foodborne pathogenic bacteria. To uncover the molecular basis of these effects, transcriptome analysis elucidated that 3201 modulates specific gene expression related to the innate immune response in C. elegans. C-type lectin-related genes and lysozyme-related genes, crucial components of the immune system, showed significant upregulation after feeding 3201 compared with OP50. These results suggested that preconditioning with 3201 may enhance the immune response against pathogens. Metabolome analysis revealed increased levels of fumaric acid and succinic acid, metabolites of the citric acid cycle, in C. elegans fed with 3201 compared with OP50. Furthermore, there was an increase in the levels of lactic acid, a well-known antimicrobial compound. This rise in lactic acid levels may have contributed to the robust defense mechanisms against pathogens. In conclusion, this study demonstrated the probiotic properties of the candidate probiotic L. rhamnosus IDCC 3201 by using multi-omics analysis.

Recent advances in antimicrobial peptide-based therapy

Antimicrobial peptides (AMPs) are a group of polypeptide chains that have the property to target and kill a myriad of microbial organisms including viruses, bacteria, protists, etc. The first discovered AMP was named gramicidin, an extract of aerobic soil bacteria. Further studies discovered that these peptides are present not only in prokaryotes but in eukaryotes as well. They play a vital role in human innate immunity and wound repair. Consequently, they have maintained a high level of intrigue among scientists in the field of immunology, especially so with the rise of antibiotic-resistant pathogens decreasing the reliability of antibiotics in healthcare. While AMPs have promising potential to substitute for common antibiotics, their use as effective replacements is barred by certain limitations. First, they have the potential to be cytotoxic to human cells. Second, they are unstable in the blood due to action by various proteolytic agents and ions that cause their degradation. This review provides an overview of the mechanism of AMPs, their limitations, and developments in recent years that provide techniques to overcome those limitations. We also discuss the advantages and drawbacks of AMPs as a replacement for antibiotics as compared to other alternatives such as synthetically modified bacteriophages, traditional medicine, and probiotics.

Improving the Therapeutic Index of Smp24, a Venom-Derived Antimicrobial Peptide: Increased Activity against Gram-Negative Bacteria

Antimicrobial peptides (AMPs) are naturally occurring compounds which possess a rapid killing mechanism and low resistance potential. Consequently, they are being viewed as potential alternatives to traditional antibiotics. One of the major factors limiting further development of AMPs is off-target toxicity. Enhancements to antimicrobial peptides which can maximise antimicrobial activity whilst reducing mammalian cytotoxicity would make these peptides more attractive as future pharmaceuticals. We have previously characterised Smp24, an AMP derived from the venom of the scorpion Scorpio maurus palmatus. This study sought to better understand the relationship between the structure, function and bacterial selectivity of this peptide by performing single amino acid substitutions. The antimicrobial, haemolytic and cytotoxic activity of modified Smp24 peptides was determined. The results of these investigations were compared with the activity of native Smp24 to determine which modifications produced enhanced therapeutic indices. The structure–function relationship of Smp24 was investigated by performing N-terminal, mid-chain and C-terminal amino acid substitutions and determining the effect that they had on the antimicrobial and cytotoxic activity of the peptide. Increased charge at the N-, mid- and C-termini of the peptide resulted in increased antimicrobial activity. Increased hydrophobicity at the N-terminus resulted in reduced haemolysis and cytotoxicity. Reduced antimicrobial, haemolytic and cytotoxic activity was observed by increased hydrophobicity at the mid-chain. Functional improvements have been made to modified peptides when compared with native Smp24, which has produced peptides with enhanced therapeutic indices.

iTRAQ-Based Comparative Proteomic Analysis of Larval Midgut From the Beet Armyworm, Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) Challenged With the Entomopathogenic Bacteria Serratia marcescens

Entomopathogenic bacteria Serratia marcescens is widely used as an environmentally friendly biocontrol agent against various pests, including Spodoptera exigua. Understanding the immune defense mechanism of S. exigua through comparative proteomic analysis can identify the key proteins expressed in response to the microbial infection. Here, we employed the as isobaric tags for relative and absolute quantification (iTRAQ) technique to investigate the effects of S. marcescens on the proteomic expression of S. exigua. Based on the molecular functional analysis, the differentially expressed proteins (DEPs) were mainly involved in the binding process and catalytic activities. Further bioinformatics analysis revealed important DEPs that played a crucial role in innate immunity of S. exigua with recognition (C-type lectin), melanization (propanol oxidase 3, serine protease, Serine-type carboxypeptidase activity, clip domain serine protease 4), antimicrobial activity (lysozyme, lysozyme-like, gloverin, cecropin B), detoxification (acetyl-CoA C-acetyltransferase, 3-dehydroecdysone 3-alpha-reductase, glucuronosyltransferase, glutathione S-transferase) and others. The Quantitative real-time PCR (qRT-PCR) results further indicated the significant upregulation of the immune-related genes in Spodoptera exigua following S. marcescens infection. To the best of our knowledge, this is the first iTRAQ based study to characterize S. marcescens mediated proteomic changes in S. exigua and identified important immune-related DEPs. The results of this study will provide an essential resource for understanding the host-pathogen interactions and the development of novel microbial biopesticides against various pests.

DAF-16 and SMK-1 Contribute to Innate Immunity During Adulthood in Caenorhabditis elegans

Aging is accompanied by a progressive decline in immune function termed "immunosenescence". Deficient surveillance coupled with the impaired function of immune cells compromises host defense in older animals. The dynamic activity of regulatory modules that control immunity appears to underlie age-dependent modifications to the immune system. In the roundworm Caenorhabditis elegans levels of PMK-1 p38 MAP kinase diminish over time, reducing the expression of immune effectors that clear bacterial pathogens. Along with the PMK-1 pathway, innate immunity in C. elegans is regulated by the insulin signaling pathway. Here we asked whether DAF-16, a Forkhead box (FOXO) transcription factor whose activity is inhibited by insulin signaling, plays a role in host defense later in life. While in younger C. elegans DAF-16 is inactive unless stimulated by environmental insults, we found that even in the absence of acute stress the transcriptional activity of DAF-16 increases in an age-dependent manner. Beginning in the reproductive phase of adulthood, DAF-16 upregulates a subset of its transcriptional targets, including genes required to kill ingested microbes. Accordingly, DAF-16 has little to no role in larval immunity, but functions specifically during adulthood to confer resistance to bacterial pathogens. We found that DAF-16-mediated immunity in adults requires SMK-1, a regulatory subunit of the PP4 protein phosphatase complex. Our data suggest that as the function of one branch of the innate immune system of C. elegans (PMK-1) declines over time, DAF-16-mediated immunity ramps up to become the predominant means of protecting adults from infection, thus reconfiguring immunity later in life.

Trematocine, a Novel Antimicrobial Peptide from the Antarctic Fish Trematomus bernacchii: Identification and Biological Activity

Antimicrobial peptides (AMPs) are short peptides active against a wide range of pathogens and, therefore, they are considered a useful alternative to conventional antibiotics. We have identified a new AMP in a transcriptome derived from the Antarctic fish Trematomus bernacchii. This peptide, named Trematocine, has been investigated for its expression both at the basal level and after in vivo immunization with an endemic Antarctic bacterium (Psychrobacter sp. TAD1). Results agree with the expected behavior of a fish innate immune component, therefore we decided to synthesize the putative mature sequence of Trematocine to determine the structure, the interaction with biological membranes, and the biological activity. We showed that Trematocine folds into a α-helical structure in the presence of both zwitterionic and anionic charged vesicles. We demonstrated that Trematocine has a highly specific interaction with anionic charged vesicles and that it can kill Gram-negative bacteria, possibly via a carpet like mechanism. Moreover, Trematocine showed minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values against selected Gram-positive and Gram-negative bacteria similar to other AMPs isolated from Antarctic fishes. The peptide is a possible candidate for a new drug as it does not show any haemolytic or cytotoxic activity against mammalian cells at the concentration needed to kill the tested bacteria.

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.

The Saposin-Like Protein AplD Displays Pore-Forming Activity and Participates in Defense Against Bacterial Infection During a Multicellular Stage of Dictyostelium discoideum

Due to their archaic life style and microbivor behavior, amoebae may represent a source of antimicrobial peptides and proteins. The amoebic protozoon Dictyostelium discoideum has been a model organism in cell biology for decades and has recently also been used for research on host-pathogen interactions and the evolution of innate immunity. In the genome of D. discoideum, genes can be identified that potentially allow the synthesis of a variety of antimicrobial proteins. However, at the protein level only very few antimicrobial proteins have been characterized that may interact directly with bacteria and help in fighting infection of D. discoideum with potential pathogens. Here, we focus on a large group of gene products that structurally belong to the saposin-like protein (SAPLIP) family and which members we named provisionally Apls (amoebapore-like peptides) according to their similarity to a comprehensively studied antimicrobial and cytotoxic pore-forming protein of the protozoan parasite Entamoeba histolytica. We focused on AplD because it is the only Apl gene that is reported to be primarily transcribed further during the multicellular stages such as the mobile slug stage. Upon knock-out (KO) of the gene, aplD⁻ slugs became highly vulnerable to virulent Klebsiella pneumoniae. AplD⁻ slugs harbored bacterial clumps in their interior and were unable to slough off the pathogen in their slime sheath. Re-expression of AplD in aplD⁻ slugs rescued the susceptibility toward K. pneumoniae. The purified recombinant protein rAplD formed pores in liposomes and was also capable of permeabilizing the membrane of live Bacillus megaterium. We propose that the multifarious Apl family of D. discoideum comprises antimicrobial effector polypeptides that are instrumental to interact with bacteria and their phospholipid membranes. The variety of its members would allow a complementary and synergistic action against a variety of microbes, which the amoeba encounters in its environment.

Antimicrobial effectors in the nematode Caenorhabditis elegans: an outgroup to the Arthropoda

Nematodes and arthropods likely form the taxon Ecdysozoa. Information on antimicrobial effectors from the model nematode Caenorhabditis elegans may thus shed light on the evolutionary origin of these defences in arthropods. This nematode species possesses an extensive armory of putative antimicrobial effector proteins, such as lysozymes, caenopores (or saposin-like proteins), defensin-like peptides, caenacins and neuropeptide-like proteins, in addition to the production of reactive oxygen species and autophagy. As C. elegans is a bacterivore that lives in microbe-rich environments, some of its effector peptides and proteins likely function in both digestion of bacterial food and pathogen elimination. In this review, we provide an overview of C. elegans immune effector proteins and mechanisms. We summarize the experimental evidence of their antimicrobial function and involvement in the response to pathogen infection. We further evaluate the microbe-induced expression of effector genes using WormExp, a recently established database for C. elegans gene expression analysis. We emphasize the need for further analysis at the protein level to demonstrate an antimicrobial activity of these molecules both in vitro and in vivoThis article is part of the themed issue 'Evolutionary ecology of arthropod antimicrobial peptides'.

Evolution of Cell-Autonomous Effector Mechanisms in Macrophages versus Non-Immune Cells

Specialized adaptations for killing microbes are synonymous with phagocytic cells including macrophages, monocytes, inflammatory neutrophils, and eosinophils. Recent genome sequencing of extant species, however, reveals that analogous antimicrobial machineries exist in certain non-immune cells and also within species that ostensibly lack a well-defined immune system. Here we probe the evolutionary record for clues about the ancient and diverse phylogenetic origins of macrophage killing mechanisms and how some of their properties are shared with cells outside the traditional bounds of immunity in higher vertebrates such as mammals.

Screening and Optimizing Antimicrobial Peptides by Using SPOT-Synthesis

Peptide arrays on cellulose are a powerful tool to investigate peptide interactions with a number of different molecules, for examples antibodies, receptors or enzymes. Such peptide arrays can also be used to study interactions with whole cells. In this review, we focus on the interaction of small antimicrobial peptides with bacteria. Antimicrobial peptides (AMPs) can kill multidrug-resistant (MDR) human pathogenic bacteria and therefore could be next generation antibiotics targeting MDR bacteria. We describe the screen and the result of different optimization strategies of peptides cleaved from the membrane. In addition, screening of antibacterial activity of peptides that are tethered to the surface is discussed. Surface-active peptides can be used to protect surfaces from bacterial infections, for example implants.

Macrobrachium rosenbergii mannose binding lectin: synthesis of MrMBL-N20 and MrMBL-C16 peptides and their antimicrobial characterization, bioinformatics and relative gene expression analysis

Mannose-binding lectin (MBL), an antimicrobial protein, is an important component of innate immune system which recognizes repetitive sugar groups on the surface of bacteria and viruses leading to activation of the complement system. In this study, we reported a complete molecular characterization of cDNA encoded for MBL from freshwater prawn Macrobrachium rosenbergii (Mr). Two short peptides (MrMBL-N20: (20)AWNTYDYMKREHSLVKPYQG(39) and MrMBL-C16: (307)GGLFYVKHKEQQRKRF(322)) were synthesized from the MrMBL polypeptide. The purity of the MrMBL-N20 (89%) and MrMBL-C16 (93%) peptides were confirmed by MS analysis (MALDI-ToF). The purified peptides were used for further antimicrobial characterization including minimum inhibitory concentration (MIC) assay, kinetics of bactericidal efficiency and analysis of hemolytic capacity. The peptides exhibited antimicrobial activity towards all the Gram-negative bacteria taken for analysis, whereas they showed the activity towards only a few selected Gram-positive bacteria. MrMBL-C16 peptides produced the highest inhibition towards both the Gram-negative and Gram-positive bacteria compared to the MrMBL-N20. Both peptides do not produce any inhibition against Bacillus sps. The kinetics of bactericidal efficiency showed that the peptides drastically reduced the number of surviving bacterial colonies after 24 h incubation. The results of hemolytic activity showed that both peptides produced strong activity at higher concentration. However, MrMBL-C16 peptide produced the highest activity compared to the MrMBL-N20 peptide. Overall, the results indicated that the peptides can be used as bactericidal agents. The MrMBL protein sequence was characterized using various bioinformatics tools including phylogenetic analysis and structure prediction. We also reported the MrMBL gene expression pattern upon viral and bacterial infection in M. rosenbergii gills. It could be concluded that the prawn MBL may be one of the important molecule which is involved in antimicrobial mechanism. Moreover, MrMBL derived MrMBL-N20 and MrMBL-C16 peptides are important antimicrobial peptides for the recognition and eradication of viral and bacterial pathogens.

Characterization of a novel anti-lipopolysaccharide factor isoform (SpALF5) in mud crab, Scylla paramamosain

Anti-lipopolysaccharide factors (ALFs), the potential antimicrobial peptides that bind and neutralize lipopolysaccharide (LPS), are common effectors of innate immunity in crustaceans. In this study, a novel isoform of ALFs (SpALF5) was isolated from the hemocytes of mud crab Scylla paramamosain. The full-length 975bp SpALF5 contains a 375bp open reading frame (ORF) encoding 125 amino acids. Although SpALF5 exhibits a low degree of nucleotide homology with other reported ALFs, it contains the conserved amino acid sequence with a signal peptide and a LPS-binding domain including two conservative cysteine residues. The genomic organization of SpALF5 consists of four exons and three introns, with each intron containing one or more tandem repeats. Unlike most of ALFs mainly distributed in crab hemocytes, SpALF5 transcript was predominantly observed in the brain, muscle and skin, while barely detected in the hemocytes in our study. In situ hybridization assay also showed that SpALF5 mRNA was localized in brain, muscle and skin tissues of mud crab. Further, SpALF5 transcript was significantly up-regulated after challenge with LPS, polyinosinic polycytidylic acid (PolyI:C) (with the except of that in brain), Vibrio parahemolyticus or white spot syndrome virus (WSSV). The recombinant SpALF5 protein showed a varying degree of binding activity towards bacteria and fungus. Moreover, in vitro, the recombinant SpALF5 revealed a strong antimicrobial activity against Gram-negative bacteria (V. parahemolyticus, Vibrio alginolyticus, Escherichia coli, Aeromonas hydrophila) and fungus (Sacchromyces cerevisiae), but could only inhibited the growth of some Gram-positive bacteria like Staphylococcus aureus. The results suggest that SpALF5 is a potent immune protector and plays an important role in immune defense against invading pathogens in S. paramamosain.

Quantitative proteome analysis of Caenorhabditis elegans upon exposure to nematicidal Bacillus thuringiensis

Caenorhabditis elegans can be infected by a plethora of pathogens, most of them are also pathogenic for humans. Consequently, the nematode has emerged as a powerful surrogate host to model microbial human infectious diseases in a non-vertebrate, for the study of innate immunity and host-pathogen interactions. Signaling cascades are well investigated that face bacterial or fungal pathogens. We analyzed the downstream processes of these cascades, i.e. the differential expression of effector and regulatory molecules due to a microbial challenge with a pathogenic strain of the bacterium Bacillus thuringiensis (Bt) in comparison to a non-pathogenic Bt strain. The protein abundance profile of the nematode was studied by quantitative proteomics using iTRAQ labeling and 2D-LC-MS analysis. We developed (i) a novel method for the preparation of defined C. elegans samples; (ii) a pooling strategy for fractions in 2D-LC separation schemes; and (iii) an isobaric labeling scheme reducing the number of necessary LC-MS experiments. More than 3,600 proteins were quantified, 288 of which showed altered abundances, implicating protein classes such as lectins, lysozymes, and transthyretin-like proteins to be involved in the nematode innate immune defense. A number of gene products previously only identified by transcriptomic profiling could be verified at the protein level. Moreover, several other protein classes such as proteases, proteins related to autophagy and apoptosis, structural proteins, and proteins involved in chromatin organization were detected. The results provide an overview of the physiological response towards a pathogen at protein level in the important model organism C. elegans, giving insights into highly complex host-pathogen interactions.

BIOLOGICAL SIGNIFICANCE

This study identified system-wide effects of Bt intoxication on C. elegans at protein level, expanding the catalogue of immune effectors potentially acting towards the pathogen, and provide verification for numerous gene products implicated in previous transcriptomic studies. The data present evidence in support of both a general defense response as well as a specific reaction against the Bt toxin within the nematode. The described findings will also contribute to a deeper understanding of host-microbe interaction in other organisms, including humans, and may provide key information that touches far reaching aspects of coevolutionary processes.

Orthosiphon stamineus protects Caenorhabditis elegans against Staphylococcus aureus infection through immunomodulation

Amidst growing concerns over the spread of antibiotic-resistant Staphylococcus aureus strains, the identification of alternative therapeutic molecules has become paramount. Previously, we utilized a Caenorhabditis elegans–S. aureus screening platform to identify potential anti-infective agents from a collection of natural extracts and synthetic compounds. One of the hits obtained from the screen was the aqueous extract of Orthosiphon stamineus leaves (UE-12) that enhanced the survival of infected nematodes without interfering with bacterial growth. In this study, we used a fluorescent transgenic reporter strain and observed that the repressed expression of the lys-7 defense gene in infected nematodes was restored in the presence of UE-12. Analysis of a selected panel of PMK-1 and DAF-16-regulated transcripts and loss-of-function mutants in these pathways indicates that the protective role of UE-12 is mediated via the p38 MAP kinase and insulin-like signaling pathways. Further analysis of a panel of known bioactive compounds of UE-12 proposed eupatorin (C₁₈H₁₆O₇) as the possible candidate active molecule contributing to the anti-infective property of UE-12. Taken together, these findings strongly suggest that the O. stamineus leaf extract is a promising anti-infective agent that confers an advantage in survival against S. aureus infection by modulating the immune response of the infected host.

Expression, Purification, and Characteristic of Tibetan Sheep Breast Lysozyme Using Pichia pastoris Expression System

A lysozyme gene from breast of Tibetan sheep was successfully expressed by secretion using a-factor signal sequence in the methylotrophic yeast, Pichia pastoris GS115. An expression yield and specific activity greater than 500 mg/L and 4,000 U/mg was obtained. Results at optimal pH and temperature showed recombinant lysozyme has higher lytic activity at pH 6.5 and 45°C. This study demonstrates the successful expression of recombinant lysozyme using the eukaryotic host organism P. pastoris paving the way for protein engineering. Additionally, this study shows the feasibility of subsequent industrial manufacture of the enzyme with this expression system together with a high purity scheme for easy high-yield purification.

A novel single-domain peptide, anti-LPS factor from prawn: synthesis of peptide, antimicrobial properties and complete molecular characterization

In this study, we reported a complete molecular characterization including bioinformatics features, gene expression, peptide synthesis and its antimicrobial activities of an anti-lipopolysaccharide (LPS) factor (ALF) cDNA identified from the established cDNA library of freshwater prawn Macrobrachium rosenbergii (named as MrALF). The mature protein has an estimated molecular weight of 11.240 kDa with an isoelectric point of 9.46. The bioinformatics analysis showed that the MrALF contains an antimicrobial peptide (AMP) region between T54 and P77 with two conserved cysteine residues (Cys55 and Cys76) which have an anti-parallel β-sheet confirmation. The β-sheet is predicted as cationic with hydrophobic nature containing a net charge of +5. The depicted AMP region is determined to be amphipathic with a predicted hydrophobic face 'FPVFI'. A highest MrALF gene expression was observed in hemocytes and is up-regulated with virus [white spot syndrome baculovirus (WSBV)], bacteria (Aeromonas hydrophila) and Escherichia coli LPS at various time points. The LPS binding region of MrALF peptide was synthesized to study the antimicrobial property, bactericidal efficiency and hemolytic capacity. The peptide showed antimicrobial activity against both the Gram-negative and Gram-positive bacteria. The bactericidal assay showed that the peptide recognized the LPS of bacterial cell walls and binding on its substrate and thereby efficiently distinguishing the pathogens. The hemolytic activity of MrALF peptide is functioning in a concentration dependant manner. In summary, the comprehensive analysis of MrALF showed it to be an effective antimicrobial peptide and thus it plays a crucial role in the defense mechanism of M. rosenbergii.

Antimicrobial peptides

The rapid increase in drug-resistant infections has presented a serious challenge to antimicrobial therapies. The failure of the most potent antibiotics to kill “superbugs” emphasizes the urgent need to develop other control agents. Here we review the history and new development of antimicrobial peptides (AMPs), a growing class of natural and synthetic peptides with a wide spectrum of targets including viruses, bacteria, fungi, and parasites. We summarize the major types of AMPs, their modes of action, and the common mechanisms of AMP resistance. In addition, we discuss the principles for designing effective AMPs and the potential of using AMPs to control biofilms (multicellular structures of bacteria embedded in extracellular matrixes) and persister cells (dormant phenotypic variants of bacterial cells that are highly tolerant to antibiotics).

Immune mediators of sea-cucumber Holothuria tubulosa (Echinodermata) as source of novel antimicrobial and anti-staphylococcal biofilm agents

The present study aims to investigate coelomocytes, immune mediators cells in the echinoderm Holothuria tubulosa, as an unusual source of antimicrobial and antibiofilm agents. The activity of the 5kDa peptide fraction of the cytosol from H. tubulosa coelomocytes (5-HCC) was tested against a reference group of Gram-negative and Gram-positive human pathogens. Minimal inhibitory concentrations (MICs) ranging from 125 to 500 mg/ml were determined against tested strains. The observed biological activity of 5-HCC could be due to two novel peptides, identified by capillary RP-HPLC/nESI-MS/MS, which present the common chemical-physical characteristics of antimicrobial peptides. Such peptides were chemically synthesized and their antimicrobial activity was tested. The synthetic peptides showed broad-spectrum activity at 12.5 mg/ml against the majority of the tested Gram-positive and Gram-negative strains, and they were also able to inhibit biofilm formation in a significant percentage at a concentration of 3.1 mg/ml against staphylococcal and Pseudomonas aeruginosa strains.

The immune mediators in H. tubulosa are a source of novel antimicrobial peptides for the development of new agents against biofilm bacterial communities that are often intrinsically resistant to conventional antibiotics.

Structure and function of a unique pore-forming protein from a pathogenic acanthamoeba

Human pathogens often produce soluble protein toxins that generate pores inside membranes, resulting in the death of target cells and tissue damage. In pathogenic amoebae, this has been exemplified with amoebapores of the enteric protozoan parasite Entamoeba histolytica. Here we characterize acanthaporin, to our knowledge the first pore-forming toxin to be described from acanthamoebae, which are free-living, bacteria-feeding, unicellular organisms that are opportunistic pathogens of increasing importance and cause severe and often fatal diseases. We isolated acanthaporin from extracts of virulent Acanthamoeba culbertsoni by tracking its pore-forming activity, molecularly cloned the gene of its precursor and recombinantly expressed the mature protein in bacteria. Acanthaporin was cytotoxic for human neuronal cells and exerted antimicrobial activity against a variety of bacterial strains by permeabilizing their membranes. The tertiary structures of acanthaporin's active monomeric form and inactive dimeric form, both solved by NMR spectroscopy, revealed a currently unknown protein fold and a pH-dependent trigger mechanism of activation.

SPP-3, a saposin-like protein of Caenorhabditis elegans, displays antimicrobial and pore-forming activity and is located in the intestine and in one head neuron

Caenopores belong to the saposin-like protein superfamily in Caenorhabditis elegans with 33 putative antimicrobial and pore-forming proteins. In this study, we analysed one selected member of this multifarious protein family, namely SPP-3, in detail, as its coding gene has been described to be inducible after bacterial challenge. The recombinant protein was antimicrobially active against a wide range of gram-negative and gram-positive bacteria and displayed membrane-permeabilizing and pH-dependent pore-forming activity. Promoter activity of the respective gene, spp-3, was localized to the intestine and the head neuron SDQR. While gene silencing had no apparent effect on the number of surviving Escherichia coli bacteria in the intestine, it increased the egg laying significantly. Accordingly, SPP-3 is a protein with antimicrobial activity that is presumably part of the redundant armamentarium of effector proteins in the worm's intestine, may help to protect neurons, and appears to be involved in regulating reproduction.

Studies on Shigella boydii infection in Caenorhabditis elegans and bioinformatics analysis of immune regulatory protein interactions

Shigella boydii causes bacillary dysentery or shigellosis and generates a significant burden in the developing nations. S. boydii-mediated infection assays were performed at both physiological and molecular levels using Caenorhabditis elegans as a host. Continuous exposure of worms to S. boydii showed a reduced life span indicating the pathogenicity of Shigella. Quantitative Real-Time PCR analysis was performed to analyze the expression and regulation of host specific candidate-antimicrobial genes (clec-60, clec-87, lys-7), which were expressed significantly during early infection, but weakened during the latter hours. Increased mortality of mutant RB1285 by S. boydii and Shigella flexneri indicated the role of lys-7 during Shigella infection. Protein-protein interactions (PPIs) database was used to analyze the interaction of immune proteins in both C. elegans and humans. In addition, the expression and regulation were revealed about immune genes (clec-61, clec-62, clec-63, F54D5.3 and ZK1320.2), which encode several intermediate immune protein partners (CLEC-61, CLEC-62, CLEC-63, F54D5.3, ZK1320.2, W03D2.6 and THN-2) that interact with LYS-7 and CLEC-60 and were found to play a role in C. elegans immune defense against S. boydii infections. Similarly, the immune genes that are specific to the human defense system, which encode IGHV4-39, A2M, LTF, and CD79A, were predicted to be expressed with LYZ and MBL2, thus indicating their regulation during Shigella infections. Our results using the lowest eukaryotic model system and human database indicated that the major players involved in immunity-related processes appear to be common in cases of Shigella sp. mediated immune responses. This article is part of a Special Issue entitled: Computational Methods for Protein Interaction and Structural Prediction.

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.

Localization of antimicrobial peptides in the tunic of Ciona intestinalis (Ascidiacea, Tunicata) and their involvement in local inflammatory-like reactions

Tunicates comprising a wide variety of different species synthesize antimicrobial peptides as important effector molecules of the innate immune system. Recently, two putative gene families coding for antimicrobial peptides were identified in the expressed sequence tag database of the tunicate Ciona intestinalis. Two synthetic peptides representing the cationic core region of one member of each of the families displayed potent antibacterial and antifungal activities. Moreover, the natural peptides were demonstrated to be synthesized and stored in distinct hemocyte types. Here, we investigated the presence of these natural peptides, namely Ci-MAM-A and Ci-PAP-A, in the tunic of C. intestinalis considering that the ascidian tunic is a body surface barrier exposed to constant microbial assault. Furthermore, as the tunic may represent a major route of entry for pathogen invasion after its damage we monitored the location of these peptides upon a local inflammatory-like reaction induced by injection of foreign cells. Using immunocytochemistry and electron microscopy both peptides were localized to the tunic and were massively present in granulocytes of inflamed tissue. Conclusively, antimicrobial peptides may constitute a chemical barrier within the tunic of urochordates.

Protist-type lysozymes of the nematode Caenorhabditis elegans contribute to resistance against pathogenic Bacillus thuringiensis

Pathogens represent a universal threat to other living organisms. Most organisms express antimicrobial proteins and peptides, such as lysozymes, as a protection against these challenges. The nematode Caenorhabditis elegans harbours 15 phylogenetically diverse lysozyme genes, belonging to two distinct types, the protist- or Entamoeba-type (lys genes) and the invertebrate-type (ilys genes) lysozymes. In the present study we characterized the role of several protist-type lysozyme genes in defence against a nematocidal strain of the Gram-positive bacterium Bacillus thuringiensis. Based on microarray and subsequent qRT-PCR gene expression analysis, we identified protist-type lysozyme genes as one of the differentially transcribed gene classes after infection. A functional genetic analysis was performed for three of these genes, each belonging to a distinct evolutionary lineage within the protist-type lysozymes (lys-2, lys-5, and lys-7). Their knock-out led to decreased pathogen resistance in all three cases, while an increase in resistance was observed when two out of three tested genes were overexpressed in transgenic lines (lys-5, lys-7, but not lys-2). We conclude that the lysozyme genes lys-5, lys-7, and possibly lys-2 contribute to resistance against B. thuringiensis, thus highlighting the particular role of lysozymes in the nematode's defence against pathogens.

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.

Analysis of Shigella flexneri-mediated infections in model organism Caenorhabditis elegans

BACKGROUND

Shigella flexneri is the causative agent of bacillary dysentery and generates a significant global disease burden. The aim of this study was to analyze the pathogenesis and host immune response, at both the physiological and molecular level, using the model organism Caenorhabditis elegans, in response to S. flexneri. C. elegans is a nematode that responds to infection with a simple innate immune system, key aspects of which have been shown to be conserved.

METHODS

S. flexneri-mediated infection of C. elegans was performed in both solid and liquid assays. The expression and subsequent regulation of host candidate antimicrobial genes such as lysozymes, C-type lectins and pathogen virulence genes were kinetically analyzed in the S. flexneri-exposed nematode.

RESULTS

In solid assays, worms fed with S. flexneri showed complete killing at 153 ± 9 h. The kinetic studies showed that S. flexneri killed the worms upon continuous exposure at 41 ± 1.7 h. However, short-time exposure of the host to S. flexneri indicated that 14 h of exposure resulted in a loss of progeny, and death occurred after 46 h. Semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed that mRNA levels of host candidate antimicrobial genes and pathogen virulence genes varied significantly at the time of early infection.

CONCLUSIONS

The killing of C. elegans requires live bacteria, and a minimal exposure time is sufficient for S. flexneri to have a lethal effect. The candidate antimicrobial genes and virulence genes are kinetically regulated within C. elegans during S. flexneri-mediated infections, thereby exhibiting their role and contribution in the host innate immune system.

[Insect antimicrobial peptides: structures, properties and gene regulation]

Insect antimicrobial peptides (AMPs) are an important group of insect innate immunity effectors. Insect AMPs are cationic and contain less than 100 amino acid residues. According to structure, insect AMPs can be divided into a limited number of families. The diverse antimicrobial spectrum of insect AMPs may indicate different modes of action. Research on the model organism Drosophila indicate that insect AMPs gene regulation involves multiple signaling pathways and a large number of signaling molecules.

Caenopores are antimicrobial peptides in the nematode Caenorhabditis elegans instrumental in nutrition and immunity

For the soil nematode Caenorhabditis elegans, microbes are both food source and potential pathogens. Intrinsic antibiotic agents such as antimicrobial peptides (AMP) are important to protect the worm against infection. Here, we show that among potential antimicrobial peptides of C. elegans, with respect to gene number, the majority belongs to the SPP-protein family which we named caenopores as they resemble structurally and functionally amoebapores. SPP-5 kills bacteria by permeabilizing their cytoplasmic membrane and displays pore-forming activity as judged by liposome depolarization. The antimicrobial polypeptide is required to cope with Escherichia coli, the regular food source of C. elegans in the laboratory, as worms devoid of this weapon develop poorly, permitting a substantial number of bacteria to survive in the intestine. As numerous caenopores exert their activity in the intestinal lumen, an environment mimicking with its acidic pH and the presence of hydrolytic enzymes, the interior of phagolysosomes, individual members may be operative in eliminating distinct groups of microorganisms that enter this tract by food consumption. Individual spp genes are induced upon contact with particular bacteria, whereas others are expressed regardless of the bacteria they live on. The multifarious caenopore family of antimicrobial peptides may have been a key event that enables C. elegans to live and survive in its natural habitat, on rotting organic material.

Surfactant protein B propeptide contains a saposin-like protein domain with antimicrobial activity at low pH

Surfactant protein B (SP-B) proprotein contains three saposin-like protein (SAPLIP) domains: a SAPLIP domain corresponding to the mature SP-B peptide is essential for lung function and postnatal survival; the function of SAPLIP domains in the N-terminal (SP-BN) and C-terminal regions of the proprotein is not known. In the current study, SP-BN was detected in the supernatant of mouse bronchoalveolar lavage fluid (BALF) and in nonciliated bronchiolar cells, alveolar type II epithelial cells, and alveolar macrophages. rSP-BN indirectly promoted the uptake of bacteria by macrophage cell lines and directly killed bacteria at acidic pH, consistent with a lysosomal, antimicrobial function. Native SP-BN isolated from BALF also killed bacteria but only at acidic pH; the bactericidal activity of BALF at acidic pH was completely blocked by SP-BN Ab. Transgenic mice overexpressing SP-BN and mature SP-B peptide had significantly decreased bacterial burden and increased survival following intranasal inoculation with bacteria. These findings support the hypothesis that SP-BN contributes to innate host defense of the lung by supplementing the nonoxidant antimicrobial defenses of alveolar macrophages.

In-silico homology modeling of three isoforms of insect defensins from the dengue vector mosquito, Aedes aegypti (Linn., 1762)

Dengue is a serious public health problem in tropical and subtropical countries. It is caused by any of the four serologically distinct dengue viruses, namely DENV1-4. The viruses are transmitted by Aedes mosquitoes. Understanding various defence mechanisms of insects has become a prime area of research worldwide. In insects, the first line of defence against invading pathogens includes cellular mechanisms and a battery of antimicrobial peptides such as defensins, cecropins etc. Defensins--cationic, cysteine-rich peptides consisting of approximately 40 amino acids with broad-spectrum activity against Gram-positive bacteria--have been reported from a wide range of organisms. In the dengue vector mosquito, Aedes aegypti, three isoforms of defensins are reported to be expressed in a spatial and temporal fashion. This report presents the three-dimensional structures of the three isoforms of Ae. aegypti defensins predicted by comparative modeling. Prediction was done with Modeller 9v1 and the structures validated through a series of tests. The best results of the prediction study are presented, and may help lead to the discovery of new synthetic peptides or derivatives of defensins that could be useful in the control of vector-borne diseases.

First isolation of a novel thermostable antifungal peptide secreted by Aspergillus clavatus

A novel antifungal peptide produced by an indigenous fungal strain (VR) of Aspergillus clavatus was purified. The antifungal peptide was enriched in the supernatant after heat treatment at 70 degrees C. The thermostable character was exploited in the first purification step, as purified peptide was obtained after ultrafiltration and reverse phase-HPLC on C18 column application. The purified peptide named "AcAFP" for A. clavatus antifungal peptide, has molecular mass of 5773Da determined by MALDI-ToF spectrometry. The N-terminal sequence showed a notable identity to the limited family of antifungal peptides produced by ascomycetes fungi. The AcAFP activity remains intact even after heat treatment at 100 degrees C for 1h confirming its thermostability. It exhibits a strong inhibitory activity against mycelial growth of several serious human and plant pathogenic fungi: Fusariuym oxysporum, Fusarium solani, Aspergillus niger, Botrytis cinerea, Alternaria solani, whereas AcAFP did not affect yeast and bacterial growth.

Diversification and adaptive sequence evolution of Caenorhabditis lysozymes (Nematoda: Rhabditidae)

BACKGROUND

Lysozymes are important model enzymes in biomedical research with a ubiquitous taxonomic distribution ranging from phages up to plants and animals. Their main function appears to be defence against pathogens, although some of them have also been implicated in digestion. Whereas most organisms have only few lysozyme genes, nematodes of the genus Caenorhabditis possess a surprisingly large repertoire of up to 15 genes.

RESULTS

We used phylogenetic inference and sequence analysis tools to assess the evolution of lysozymes from three congeneric nematode species, Caenorhabditis elegans, C. briggsae, and C. remanei. Their lysozymes fall into three distinct clades, one belonging to the invertebrate-type and the other two to the protist-type lysozymes. Their diversification is characterised by (i) ancestral gene duplications preceding species separation followed by maintenance of genes, (ii) ancestral duplications followed by gene loss in some of the species, and (iii) recent duplications after divergence of species. Both ancestral and recent gene duplications are associated in several cases with signatures of adaptive sequence evolution, indicating that diversifying selection contributed to lysozyme differentiation. Current data strongly suggests that genetic diversity translates into functional diversity.

CONCLUSION

Gene duplications are a major source of evolutionary innovation. Our analysis provides an evolutionary framework for understanding the diversification of lysozymes through gene duplication and subsequent differentiation. This information is expected to be of major value in future analysis of lysozyme function and in studies of the dynamics of evolution by gene duplication.

Structure and content of the Entamoeba histolytica genome

The intestinal parasite Entamoeba histolytica is one of the first protists for which a draft genome sequence has been published. Although the genome is still incomplete, it is unlikely that many genes are missing from the list of those already identified. In this chapter we summarise the features of the genome as they are currently understood and provide previously unpublished analyses of many of the genes.

Specificity of the innate immune system and diversity of C-type lectin domain (CTLD) proteins in the nematode Caenorhabditis elegans

The nematode Caenorhabditis elegans has become an important model for the study of innate immunity. Its immune system is based on several signaling cascades, including a Toll-like receptor, three mitogen-activated protein kinases (MAPK), one transforming growth factor-beta (TGF-beta), the insulin-like receptor (ILR), and the programmed cell death (PCD) pathway. Furthermore, it also involves C-type lectin domain- (CTLD) containing proteins as well as several classes of antimicrobial effectors such as lysozymes. Almost all components of the nematode immune system have homologs in other organisms, including humans, and are therefore likely of ancient evolutionary origin. At the same time, most of them are part of a general stress response, suggesting that they only provide unspecific defense. In the current article, we re-evaluate this suggestion and explore the level of specificity in C. elegans innate immunity, i.e. the nematode's ability to mount a distinct defense response towards different pathogens. We draw particular attention to the CTLD proteins, which are abundant in the nematode genome (278 genes) and many of which show a pathogen-specific response during infection. Specificity may also be achieved through the differential activation of antimicrobial genes, distinct functions of the immunity signaling cascades as well as signal integration across pathways. Taken together, our evaluation reveals high potential for immune specificity in C. elegans that may enhance the nematode's ability to fight off pathogens.

Rab11B small GTPase regulates secretion of cysteine proteases in the enteric protozoan parasiteEntamoeba histolytica

Vesicular trafficking plays a pivotal role in the virulence of the enteric protozoan parasite Entamoeba histolytica. In the present study, we showed that one isotype of the small GTPase Rab11, EhRab11B, plays a central role in the secretion of a major virulence factor, cysteine proteases. EhRab11B did not colocalize with markers for the endoplasmic reticulum, early endosomes and lysosomes, but was partially associated with non-acidified vesicles in the endocytic pathway, likely recycling endosomes. Overexpression of EhRab11B resulted in a remarkable increase in both intracellular and secreted cysteine protease activity, concomitant with an augmentation of cytolytic activity as demonstrated by an increased ability to destroy mammalian cells. The oversecretion of cysteine proteases with EhRab11B overexpression was neither sensitive to brefeldin A nor specific to a certain cysteine protease species (e.g. CP1, 2 or 5), suggesting that these three major cysteine proteases are trafficked via an EhRab11B-associated secretory pathway, which is distinct from the classical brefeldin-sensitive pathway. Overexpression of EhRab11B also enhanced exocytosis of the incorporated fluid-phase marker, supporting the notion that it is involved in recycling. This is the first report demonstrating that Rab11 plays a central role in the transport and secretion of pathogenic factors.

Two Rab7 isotypes, EhRab7A and EhRab7B, play distinct roles in biogenesis of lysosomes and phagosomes in the enteric protozoan parasite Entamoeba histolytica

Rab7 small GTPase plays a crucial role in the regulation of trafficking to late endosomes, lysosomes and phagosomes. While most eukaryotes encode a single Rab7, the parasitic protist Entamoeba histolytica possesses nine Rab7. In this study, to understand the significance of the presence of multiple Rab7 isotypes, a role of two representative Rab7 isotypes, EhRab7A and EhRab7B, was investigated. EhRab7B was exclusively localized to acidic vacuoles containing lysosomal proteins, e.g. amoebapore-A and cysteine protease. This lysosome localization of EhRab7B was in good contrast to EhRab7A, localized to a non-acidic compartment in steady state, and only partially colocalized with lysosomal proteins. Overexpression of EhRab7B resulted in augmentation of late endosome/lysosome acidification, similar to the EhRab7A overexpression. Expression of EhRab7B-GTP mutant caused dominant-negative phenotypes including decrease in late endosome/lysosome acidification and missecretion of lysosomal proteins, while EhRab7A-GTP enhanced acidification but did not affect either intracellular or secreted cysteine protease activity. Expression of either EhRab7B or EhRab7B-GTP mutant caused defect in phagocytosis, concomitant with the disturbed formation and disassembly of prephagosomal vacuoles, the compartment previously shown to be linked to efficient ingestion. Altogether, these data indicate that the two Rab7 isotypes play distinct but co-ordinated roles in lysosome and phagosome biogenesis.

Genomic clusters, putative pathogen recognition molecules, and antimicrobial genes are induced by infection of C. elegans with M. nematophilum

The interaction between the nematode Caenorhabditis elegans and a Gram-positive bacterial pathogen, Microbacterium nematophilum, provides a model for an innate immune response in nematodes. This pathogen adheres to the rectal and post-anal cuticle of the worm, causing slowed growth, constipation, and a defensive swelling response of rectal hypodermal cells. To explore the genomic responses that the worm activates after pathogenic attack we used microarray analysis of transcriptional changes induced after 6-h infection, comparing virulent with avirulent infection. We defined 89 genes with statistically significant expression changes of at least twofold, of which 68 were up-regulated and 21 were down-regulated. Among the former, those encoding C-type lectin domains were the most abundant class. Many of the 89 genes exhibit genomic clustering, and we identified one large cluster of 62 genes, of which most were induced in response to infection. We tested 41 of the induced genes for involvement in immunity using mutants or RNAi, finding that six of these are required for the swelling response and five are required more generally for defense. Our results indicate that C-type lectins and other putative pathogen-recognition molecules are important for innate immune defense in C. elegans. We also found significant induction of genes encoding lysozymes, proteases, and defense-related proteins, as well as various domains of unknown function. The genes induced during infection by M. nematophilum appear largely distinct from genes induced by other pathogens, suggesting that C. elegans mounts pathogen-specific responses to infection.

Caenorhabditis elegans as a model for innate immunity to pathogens

The amenability of the nematode Caenorhabditis elegans for genetic analysis and other experimentation provides a powerful tool for studying host-pathogen interactions. Our current understanding of how C. elegans responds to pathogen challenges is in its infancy, but the discovery that the worm has inducible defence responses, which to some extent parallel those of other organisms, demonstrates the potential of this model organism for the study of innate immunity. Most progress in dissecting the C. elegans antimicrobial response has focused around signal transduction pathways and the expression of genes activated by the worm in response to microbial infections.

The Entamoeba histolytica Ehcp112 gene has a distal and weak promoter

Ehcp112 encodes the Entamoeba histolytica EhCP112 cysteine protease that is part of the EhCPADH complex. By in silico analysis we identified putative transcription factor-binding sites along 837 bp upstream the Ehcp112 gene ATG codon. A TATA-like motif (TATATAAA) was located at -36 to -29 bp, a GAAC box (GAACC) was found at -10 to -14 bp and an Inr sequence (TTCAAC) at -8 to -2 bp. These tripartite promoter elements are in non-canonical positions, downstream the transcription initiation site (-280 bp). We cloned four Ehcp112 promoter fragments in pBSCAT-ACT plasmid to obtain pI (355 bp), pII (681 bp), pIII (833 bp), and pIV (554 bp) constructs. In transfected trophozoites, only pIII drove CAT activity with 44% efficiency in relation to actin promoter activity. Our results showed the presence of a distal and weak promoter in the Ehcp112 gene. The active DNA region is inside the open reading frame of the Ehrab B gene, suggesting that expression of both genes could be coordinately regulated.

Structural rearrangement of model membranes by the peptide antibiotic NK-2

We have developed a novel alpha-helical peptide antibiotic termed NK-2. It efficiently kills bacteria, but not human cells, by membrane destruction. This selectivity could be attributed to the different membrane lipid compositions of the target cells. To understand the mechanisms of selectivity and membrane destruction, we investigated the influence of NK-2 on the supramolecular aggregate structure, the phase transition behavior, the acyl chain fluidity, and the surface charges of phospholipids representative for the bacterial and the human cell cytoplasmic membranes. The cationic NK-2 binds to anionic phosphatidylglycerol liposomes, causing a thinning of the membrane and an increase in the phase transition temperature. However, this interaction is not solely of electrostatic but also of hydrophobic nature, indicated by an overcompensation of the Zeta potential. Whereas NK-2 has no effect on phosphatidylcholine liposomes, it enhances the fluidity of phosphatidylethanolamine acyl chains and lowers the phase transition enthalpy of the gel to liquid cristalline transition. The most dramatic effect, however, was observed for the lamellar/inverted hexagonal transition of phosphatidylethanolamine which was reduced by more than 10 degrees C. Thus, NK-2 promotes a negative membrane curvature which can lead to the collapse of the phosphatidylethanolamine-rich bacterial cytoplasmic membrane.

Rab5-associated Vacuoles Play a Unique Role in Phagocytosis of the Enteric Protozoan Parasite Entamoeba histolytica

In mammals, Rab5 and Rab7 play a specific and coordinated role in a sequential process during phagosome maturation. Here, we report that Rab5 and Rab7 in the enteric protozoan parasite Entamoeba histolytica, EhRab5 and EhRab7A, are involved in steps that are distinct from those known for mammals. EhRab5 and EhRab7A were localized to independent small vesicular structures at steady state. Priming with red blood cells induced the formation of large vacuoles associated with both EhRab5 and EhRab7A ("prephagosomal vacuoles (PPV)") in the amoeba within an incubation period of 5-10 min. PPV emerged de novo physically and distinct from phagosomes. PPV were gradually acidified and matured by fusion with lysosomes containing a digestive hydrolase, cysteine proteinase, and a membrane-permeabilizing peptide amoebapore. After EhRab5 dissociated from PPV, 5-10 min later, the EhRab7A-PPV fused with phagosomes, and EhRab7A finally dissociated from the phagosomes. Immunoelectron and light micrographs showed that PPV contained small vesicle-like structures containing fluid-phase markers and amoebapores, which were not evenly distributed within PPV, suggesting that the mechanism was similar to multivesicular body formation in PPV generation. In contrast to Rab5 from other organisms, EhRab5 was involved exclusively in phagocytosis, but not in endocytosis. Overexpression of wild-type EhRab5 enhanced phagocytosis and the transport of amoebapore to phagosomes. Conversely, expression of an EhRab5Q67L GTP form mutant impaired the formation of PPV and phagocytosis. Altogether, we propose that the amoebic Rab5 plays an important role in the formation of unique vacuoles, which is essential for engulfment of erythrocytes and important for packaging of lysosomal hydrolases, prior to the targeting to phagosomes.

Regulation of aging and innate immunity in C. elegans

The free-living soil nematode Caenorhabditis elegans is a versatile model for the study of the genetic regulation of aging and of host-pathogen interactions. Many genes affecting multiple processes, such as neuroendocrine signalling, nutritional sensing and mitochondrial functions, have been shown to play important roles in determining the lifespan of C. elegans. The DAF-2-mediated insulin signalling pathway is the major pathway that regulates aging in this nematode and this role appears universal; neuroendrocrine signalling also affects aging in Drosophila and mice. Recent studies have shown that the innate immune function in C. elegans is modulated by signalling from the TGF-beta-like, the p38 MAPK and the DAF-2 insulin pathways. The requirement for the DAF-2 pathway in modulating aging and immunity suggests that these processes may be linked at the molecular level. It is well known that as humans age, immunosenescence occurs in which there is a general degradation of immune efficiency. However, the molecular mechanisms involved in this process remain unclear. In this review, we discuss the molecular mechanisms that modulate aging and immune response and attempt to suggest molecular links between these two processes.