The Long-Distance Transport of Some Plant Hormones and Possible Involvement of Lipid-Binding and Transfer Proteins in Hormonal Transport

Adaptation to changes in the environment depends, in part, on signaling between plant organs to integrate adaptive response at the level of the whole organism. Changes in the delivery of hormones from one organ to another through the vascular system strongly suggest that hormone transport is involved in the transmission of signals over long distances. However, there is evidence that, alternatively, systemic responses may be brought about by other kinds of signals (e.g., hydraulic or electrical) capable of inducing changes in hormone metabolism in distant organs. Long-distance transport of hormones is therefore a matter of debate. This review summarizes arguments for and against the involvement of the long-distance transport of cytokinins in signaling mineral nutrient availability from roots to the shoot. It also assesses the evidence for the role of abscisic acid (ABA) and jasmonates in long-distance signaling of water deficiency and the possibility that Lipid-Binding and Transfer Proteins (LBTPs) facilitate the long-distance transport of hormones. It is assumed that proteins of this type raise the solubility of hydrophobic substances such as ABA and jasmonates in hydrophilic spaces, thereby enabling their movement in solution throughout the plant. This review collates evidence that LBTPs bind to cytokinins, ABA, and jasmonates and that cytokinins, ABA, and LBTPs are present in xylem and phloem sap and co-localize at sites of loading into vascular tissues and at sites of unloading from the phloem. The available evidence indicates a functional interaction between LBTPs and these hormones.

Novel BRICHOS-Related Antimicrobial Peptides from the Marine Worm Heteromastus filiformis: Transcriptome Mining, Synthesis, Biological Activities, and Therapeutic Potential

Marine polychaetes represent an extremely rich and underexplored source of novel families of antimicrobial peptides (AMPs). The rapid development of next generation sequencing technologies and modern bioinformatics approaches allows us to apply them for characterization of AMP-derived genes and the identification of encoded immune-related peptides with the aid of genome and transcriptome mining. Here, we describe a universal bioinformatic approach based on the conserved BRICHOS domain as a search query for the identification of novel structurally unique AMP families in annelids. In this paper, we report the discovery of 13 novel BRICHOS-related peptides, ranging from 18 to 91 amino acid residues in length, in the cosmopolitan marine worm Heteromastus filiformis with the assistance of transcriptome mining. Two characteristic peptides with a low homology in relation to known AMPs-the α-helical amphiphilic linear peptide, consisting of 28 amino acid residues and designated as HfBRI-28, and the 25-mer β-hairpin peptide, specified as HfBRI-25 and having a unique structure stabilized by two disulfide bonds-were obtained and analyzed as potential antimicrobials. Interestingly, both peptides showed the ability to kill bacteria via membrane damage, but mechanisms of their action and spectra of their activity differed significantly. Being non-cytotoxic towards mammalian cells and stable to proteolysis in the blood serum, HfBRI-25 was selected for further in vivo studies in a lethal murine model of the Escherichia coli infection, where the peptide contributed to the 100% survival rate in animals. A high activity against uropathogenic strains of E. coli (UPEC) as well as a strong ability to kill bacteria within biofilms allow us to consider the novel peptide HfBRI-25 as a promising candidate for the clinical therapy of urinary tract infections (UTI) associated with UPEC.

Molecular Insight into Ligand Binding and Transport by the Lentil Lipid Transfer Protein Lc-LTP2: The Role of Basic Amino Acid Residues at Opposite Entrances to the Hydrophobic Cavity

Lipid transfer proteins (LTPs) realize their functions in plants due to their ability to bind and transport various ligands. Structures of many LTPs have been studied; however, the mechanism of ligand binding and transport is still not fully understood. In this work, we studied the role of Lys61 and Lys81 located near the "top" and "bottom" entrances to the hydrophobic cavity of the lentil lipid transfer protein Lc-LTP2, respectively, in these processes. Using site-directed mutagenesis, we showed that both amino acid residues played a key role in lipid binding to the protein. In experiments with calcein-loaded liposomes, we demonstrated that both the above-mentioned lysine residues participated in the protein interaction with model membranes. According to data obtained from fluorescent spectroscopy and TNS probe displacement, both amino acid residues are necessary for the ability of the protein to transfer lipids between membranes. Thus, we hypothesized that basic amino acid residues located at opposite entrances to the hydrophobic cavity of the lentil Lc-LTP2 played an important role in initial protein-ligand interaction in solution as well as in protein-membrane docking.

Marine Invertebrate Antimicrobial Peptides and Their Potential as Novel Peptide Antibiotics

Marine invertebrates constantly interact with a wide range of microorganisms in their aquatic environment and possess an effective defense system that has enabled their existence for millions of years. Their lack of acquired immunity sets marine invertebrates apart from other marine animals. Invertebrates could rely on their innate immunity, providing the first line of defense, survival, and thriving. The innate immune system of marine invertebrates includes various biologically active compounds, and specifically, antimicrobial peptides. Nowadays, there is a revive of interest in these peptides due to the urgent need to discover novel drugs against antibiotic-resistant bacterial strains, a pressing global concern in modern healthcare. Modern technologies offer extensive possibilities for the development of innovative drugs based on these compounds, which can act against bacteria, fungi, protozoa, and viruses. This review focuses on structural peculiarities, biological functions, gene expression, biosynthesis, mechanisms of antimicrobial action, regulatory activities, and prospects for the therapeutic use of antimicrobial peptides derived from marine invertebrates.

Epithelial-Immune Cell Crosstalk Determines the Activation of Immune Cells In Vitro by the Human Cathelicidin LL-37 at Low Physiological Concentrations

The only human cathelicidin, LL-37, is a host defense antimicrobial peptide with antimicrobial activities against protozoans, fungi, Gram(+) and Gram(-) bacteria, and enveloped viruses. It has been shown in experiments in vitro that LL-37 is able to induce the production of various inflammatory and anti-inflammatory cytokines and chemokines by different human cell types. However, it remains an open question whether such cytokine induction is physiologically relevant, as LL-37 exhibited its immunomodulatory properties at concentrations that are much higher (>20 μg/mL) than those observed in non-inflamed tissues (1-5 μg/mL). In the current study, we assessed the permeability of LL-37 across the Caco-2 polarized monolayer and showed that this peptide could pass through the Caco-2 monolayer with low efficiency, which predetermined its low absorption in the gut. We showed that LL-37 at low physiological concentrations (<5 μg/mL) was not able to directly activate monocytes. However, in the presence of polarized epithelial monolayers, LL-37 is able to activate monocytes through the MAPK/ERK signaling pathway and induce the production of cytokines, as assessed by a multiplex assay at the protein level. We have demonstrated that LL-37 is able to fulfill its immunomodulatory action in vivo in non-inflamed tissues at low physiological concentrations. In the present work, we revealed a key role of epithelial-immune cell crosstalk in the implementation of immunomodulatory functions of the human cathelicidin LL-37, which might shed light on its physiological action in vivo.

Design of Protegrin-1 Analogs with Improved Antibacterial Selectivity

Protegrin-1 (PG-1) is a cationic β-hairpin pore-forming antimicrobial peptide having a membranolytic mechanism of action. It possesses in vitro a potent antimicrobial activity against a panel of clinically relevant MDR ESKAPE pathogens. However, its extremely high hemolytic activity and cytotoxicity toward mammalian cells prevent the further development of the protegrin-based antibiotic for systemic administration. In this study, we rationally modulated the PG-1 charge and hydrophobicity by substituting selected residues in the central β-sheet region of PG-1 to design its analogs, which retain a high antimicrobial activity but have a reduced toxicity toward mammalian cells. In this work, eight PG-1 analogs with single amino acid substitutions and five analogs with double substitutions were obtained. These analogs were produced as thioredoxin fusions in Escherichia coli. It was shown that a significant reduction in hemolytic activity without any loss of antimicrobial activity could be achieved by a single amino acid substitution, V16R in the C-terminal β-strand, which is responsible for the PG-1 oligomerization. As the result, a selective analog with a ≥30-fold improved therapeutic index was obtained. FTIR spectroscopy analysis of analog, [V16R], revealed that the peptide is unable to form oligomeric structures in a membrane-mimicking environment, in contrast to wild-type PG-1. Analog [V16R] showed a reasonable efficacy in septicemia infection mice model as a systemic antibiotic and could be considered as a promising lead for further drug design.

Immunomodulatory Effects of the Pea Defensin Psd1 in the Caco-2/Immune Cells Co-Culture upon Candida albicans Infection

Candidiasis is one of the most common fungal diseases that can pose a threat to life in immunodeficient individuals, particularly in its disseminated form. Not only fungal invasion but also fatal infection-related inflammation are common causes of systemic candidiasis. In this study, we investigated in vitro immunomodulatory properties of the antifungal pea defensin Psd1 upon Candida albicans infection. Using the real-time PCR, we showed that Psd1 inhibited the antimicrobial peptide HBD-2 and pro-inflammatory cytokines IL-1 and IL-8 downregulation at mRNA level in epithelium cells caused by C. albicans infection. By using the Caco-2/immune cells co-culture upon C. albicans infection and the multiplex xMAP assay, we demonstrated that this pathogenic fungus induced a pronounced host defense response; however, the cytokine responses were different in the presence of dendritic cells or monocytes. We revealed that Psd1 at a low concentration (2 µM) had a pronounced immunomodulatory effect on the Caco-2/immune cells co-culture upon fungal infection. Thus, we hypothesized that the pea defensin Psd1 might be an effective agent in the treatment of candidiasis not only due to its antifungal activity, but also owing to its ability to modulate a protective immune response upon infection.

Genomic Insights into Bacterial Resistance to Proline-Rich Antimicrobial Peptide Bac7

Proline-rich antimicrobial peptides (PrAMPs) having a potent antimicrobial activity and a modest toxicity toward mammalian cells attract much attention as new templates for the development of antibiotic drugs. However, a comprehensive understanding of mechanisms of bacterial resistance development to PrAMPs is necessary before their clinical application. In this study, development of the resistance to the proline-rich bovine cathelicidin Bac7_1-22 derivative was characterized in the multidrug-resistant Escherichia coli clinical isolate causing the urinary tract infection. Three Bac7_1-22-resistant strains with ≥16-fold increase in minimal inhibitory concentrations (MICs) were selected by serially passaging after four-week experimental evolution. It was shown that in salt-containing medium, the resistance was mediated by inactivation of the SbmA transporter. The absence of salt in the selection media affected both dynamics and main molecular targets under selective pressure: a point mutation leading to the amino acid substitution N159H in the WaaP kinase responsible for heptose I phosphorylation in the LPS structure was also found. This mutation led to a phenotype with a decreased susceptibility to both the Bac7_1-22 and polymyxin B. Screening of antimicrobial activities with the use of a wide panel of known AMPs, including the human cathelicidin LL-37 and conventional antibiotics, against selected strains indicated no significant cross-resistance effects.

Bet v 1-independent sensitization to major allergens in Fagales pollen: Evidence at the T-cell level

BACKGROUND

In birch-dominated areas, allergies to pollen from trees of the order Fagales are considered to be initiated by the major birch pollen allergen Bet v 1. However, the sensitizing activity of Bet v 1-homologs in Fagales pollen might be underestimated. Allergen-specific T-cells are crucial in the sensitization process. The T-cell response to major allergens from alder, hazel, oak, hornbeam, chestnut, beech, and chestnut pollen has not yet been analyzed. Here, we characterized the cellular cross-reactivity of major allergens in Fagales pollen with Bet v 1.

METHODS

T-cell-lines (TCL) were established from allergic individuals with Aln g 1, Car b 1, Ost c 1, Cor a 1, Fag s 1, Cas s 1, and Que a 1, and tested for reactivity with Bet v 1 and synthetic overlapping 12-mer peptides representing its primary sequence. Aln g 1-specific TCL was additionally tested with Aln g 1-derived peptides and all allergens. IgE-competition experiments with Aln g 1 and Bet v 1 were performed.

RESULTS

T-cell-lines initiated with Fagales pollen allergens varied strongly in their reactivity with Bet v 1 and by the majority responded stronger to the original stimulus. Cross-reactivity was mostly restricted to the epitope Bet v 1_142-153 . No distinct cross-reactivity of Aln g 1-specific T-cells with Bet v 1 was detected. Among 22 T-cell epitopes, Aln g 1 contained two immunodominant epitopes. Bet v 1 inhibited IgE-binding to Aln g 1 less potently than Aln g 1 itself.

CONCLUSION

The cellular cross-reactivity of major Fagales pollen allergens with Bet v 1 was unincisive, particularly for Aln g 1, most akin to Bet v 1. Our results indicate that humoral and cellular responses to these allergens are not predominantly based on cross-reactivity with the major birch pollen allergen but suggest a Bet v 1-independent sensitization in individuals from birch tree-dominated areas.

Structural and Functional Characteristics of the Proline-Rich Antimicrobial Peptide Minibactenecin from Leukocytes of Domestic Goat Capra hircus

We performed structural and functional studies of minibactenecin mini-ChBac7.5Nα, a natural proline-rich cathelicidin from domestic goat Capra hircus. To identify the key residues important for the biological action of the peptide, a panel of its alanine-substituted analogues was produced. The development of E. coli resistance to the natural minibactenecin, as well as to its analogues carrying substitutions for hydrophobic amino acids in the C-terminal residues was studied. The data obtained indicate the possibility of rapid development of the resistance to this class of peptides. The main factors in the formation of the antibiotic resistance are various mutations leading to inactivation of the SbmA transporter.

Specific Binding of the α-Component of the Lantibiotic Lichenicidin to the Peptidoglycan Precursor Lipid II Predetermines Its Antimicrobial Activity

To date, a number of lantibiotics have been shown to use lipid II-a highly conserved peptidoglycan precursor in the cytoplasmic membrane of bacteria-as their molecular target. The α-component (Lchα) of the two-component lantibiotic lichenicidin, previously isolated from the Bacillus licheniformis VK21 strain, seems to contain two putative lipid II binding sites in its N-terminal and C-terminal domains. Using NMR spectroscopy in DPC micelles, we obtained convincing evidence that the C-terminal mersacidin-like site is involved in the interaction with lipid II. These data were confirmed by the MD simulations. The contact area of lipid II includes pyrophosphate and disaccharide residues along with the first isoprene units of bactoprenol. MD also showed the potential for the formation of a stable N-terminal nisin-like complex; however, the conditions necessary for its implementation in vitro remain unknown. Overall, our results clarify the picture of two component lantibiotics mechanism of antimicrobial action.

Features and Possible Applications of Plant Lipid-Binding and Transfer Proteins

In plants, lipid trafficking within and inside the cell is carried out by lipid-binding and transfer proteins. Ligands for these proteins are building and signaling lipid molecules, secondary metabolites with different biological activities due to which they perform diverse functions in plants. Many different classes of such lipid-binding and transfer proteins have been found, but the most common and represented in plants are lipid transfer proteins (LTPs), pathogenesis-related class 10 (PR-10) proteins, acyl-CoA-binding proteins (ACBPs), and puroindolines (PINs). A low degree of amino acid sequence homology but similar spatial structures containing an internal hydrophobic cavity are common features of these classes of proteins. In this review, we summarize the latest known data on the features of these protein classes with particular focus on their ability to bind and transfer lipid ligands. We analyzed the structural features of these proteins, the diversity of their possible ligands, the key amino acids participating in ligand binding, the currently known mechanisms of ligand binding and transferring, as well as prospects for possible application.

Antimicrobial Activity and Immunomodulatory Properties of Acidocin A, the Pediocin-like Bacteriocin with the Non-Canonical Structure

Pediocin-like bacteriocins are among the natural antimicrobial agents attracting attention as scaffolds for the development of a new generation of antibiotics. Acidocin A has significant structural differences from most other members of this subclass. We studied its antibacterial and cytotoxic activity, as well as effects on the permeability of E. coli membranes in comparison with avicin A, the typical pediocin-like bacteriocin. Acidocin A had a more marked tendency to form an alpha-helical structure upon contact with detergent micelles, as was shown by CD spectroscopy, and demonstrated considerably less specific mode of action: it inhibited growth of Gram-positive and Gram-negative strains, which were unsusceptible to avicin A, and disrupted the integrity of outer and inner membranes of E. coli. However, the peptide retained a low toxicity towards normal and tumor human cells. The effect of mutations in the pediocin box of acidocin A (on average, a 2-4-fold decrease in activity) was less pronounced than is usually observed for such peptides. Using multiplex analysis, we showed that acidocin A and avicin A modulated the expression level of a number of cytokines and growth factors in primary human monocytes. Acidocin A induced the production of a number of inflammatory mediators (IL-6, TNFα, MIG/CXCL9, MCP-1/CCL2, MCP-3/CCL7, and MIP-1β) and inhibited the production of some anti-inflammatory factors (IL-1RA, MDC/CCL22). We assumed that the activity of acidocin A and similar peptides produced by lactic acid bacteria might affect the functional state of the human intestinal tract, not only through direct inhibition of various groups of symbiotic and pathogenic bacteria, but also via immunomodulatory effects.

Structural Features, Mechanisms of Action, and Prospects for Practical Application of Class II Bacteriocins

Bacteriocins are antimicrobial peptides ribosomally synthesized by both Gram-negative and Gram-positive bacteria, as well as by archaea. Bacteriocins are usually active against phylogenetically related bacteria, providing competitive advantage to their producers in the natural bacterial environment. However, some bacteriocins are known to have a broader spectrum of antibacterial activity, including activity against multidrug-resistant bacterial strains. Multitude of bacteriocins studied to date are characterized by a wide variety of chemical structures and mechanisms of action. Existing classification systems for bacteriocins take into account structural features and biosynthetic pathways of bacteriocins, as well as the phylogenetic affiliation of their producing organisms. Heat-stable bacteriocins with molecular weight of less than 10 kDa from Gram-positive and Gram-negative producers are divided into post-translationally modified (class I) and unmodified peptides (class II). In recent years there has been an increasing interest in the class II bacteriocins as potential therapeutic agents that can help to combat antibiotic-resistant infections. Advantages of unmodified peptides are relative simplicity of their biotechnological production in heterologous systems and chemical synthesis. Potential for the combined use of bacteriocins with other antimicrobial agents allowing to enhance their efficacy, low probability of cross-resistance development, and ability of probiotic strains to produce bacteriocins in situ make them promising candidate compounds for creation of new drugs. The review focuses on structural diversity of the class II bacteriocins and their practical relevance.

In Vitro Modulation of Complement Activation by Therapeutically Prospective Analogues of the Marine Polychaeta Arenicin Peptides

The widespread resistance to antibiotics in pathogenic bacteria makes the development of a new generation of antimicrobials an urgent task. The development of new antibiotics must be accompanied by a comprehensive study of all of their biological activities in order to avoid adverse side-effects from their application. Some promising antibiotic prototypes derived from the structures of arenicins, antimicrobial peptides from the lugworm Arenicola marina, have been developed. Previously, we described the ability of natural arenicins -1 and -2 to modulate the human complement system activation in vitro. In this regard, it seems important to evaluate the effect of therapeutically promising arenicin analogues on complement activation. Here, we describe the complement-modulating activity of three such analogues, Ar-1[V8R], ALP1, and AA139. We found that the mode of action of Ar-1[V8R] and ALP1 on the complement was similar to that of natural arenicins, which can both activate and inhibit the complement, depending on the concentration. However, Ar-1[V8R] behaved predominantly as an inhibitor, showing only a moderate increase in C3a production in the alternative pathway model and no enhancement at all of the classical pathway of complement activation. In contrast, the action of ALP1 was characterized by a marked increase in the complement activation through the classical pathway in the concentration range of 2.5–20 μg/mL. At the same time, at higher concentrations (80–160 μg/mL), this peptide exhibited a complement inhibitory effect characteristic of the other arenicins. Peptide AA139, like other arenicins, exhibited an inhibitory effect on complement at a concentration of 160 μg/mL, but was much less pronounced. Overall, our results suggest that the effect on the complement system should be taken into account in the development of antibiotics based on arenicins.

Antifungal Activity, Structural Stability, and Immunomodulatory Effects on Human Immune Cells of Defensin from the Lentil Lens culinaris

An increase in the frequency of mycoses and spreading of multidrug-resistant fungal pathogens necessitates the search for new antifungal agents. Earlier, we isolated the novel defensin from lentil Lensculinaris seeds, designated as Lc-def, which inhibited the growth of phytopathogenic fungi. Here, we studied an antifungal activity of Lc-def against human pathogenic Candida species, structural stability of the defensin, and its immunomodulatory effects that may help to prevent fungal infection. We showed that Lc-def caused 50% growth inhibition of clinical isolates of Candida albicans, C. krusei, and C. glabrata at concentrations of 25-50 μM, but was not toxic to different human cells. The lentil defensin was resistant to proteolysis by C. albicans and was not cleaved during simulated gastroduodenal digestion. By using the multiplex xMAP assay, we showed for the first time for plant defensins that Lc-def increased the production of such essential for immunity to candidiasis pro-inflammatory cytokines as IL-12 and IL-17 at the concentration of 2 μM. Thus, we hypothesized that the lentil Lc-def and plant defensins in general may be effective in suppressing of mucocutaneous candidiasis due to their antifungal activity, high structural stability, and ability to activate a protective immune response.

Novel β-Hairpin Peptide from Marine Polychaeta with a High Efficacy against Gram-Negative Pathogens

In recent years, new antibiotics targeting multidrug resistant Gram-negative bacteria have become urgently needed. Therefore, antimicrobial peptides are considered to be a novel perspective class of antibacterial agents. In this study, a panel of novel BRICHOS-related β-hairpin antimicrobial peptides were identified in transcriptomes of marine polychaeta species. Two of them—abarenicin from Abarenicola pacifica and UuBRI-21 from Urechis unicinctus—possess strong antibacterial potential in vitro against a wide panel of Gram-negative bacteria including drug-resistant strains. Mechanism of action assays demonstrate that peptides disrupt bacterial and mammalian membrane integrity. Considering the stronger antibacterial potential and a low ability of abarenicin to be bound by components of serum, this peptide was selected for further modification. We conducted an alanine and arginine scanning of abarenicin by replacing individual amino acids and modulating hydrophobicity so as to improve its antibacterial potency and membrane selectivity. This design approach allowed us to obtain the Ap9 analog displaying a high efficacy in vivo in the mice septicemia and neutropenic mice peritonitis models. We demonstrated that abarenicin analogs did not significantly induce bacterial resistance after a four-week selection experiment and acted on different steps of the biofilm formation: (a) killing bacteria at their planktonic stage and preventing biofilm formation and (b) degrading pre-formed biofilm and killing embedded bacteria. The potent antibacterial and antibiofilm activity of the abarenicin analog Ap9 with its high efficacy in vivo against Gram-negative infection in mice models makes this peptide an attractive candidate for further preclinical investigation.

How Do Pollen Allergens Sensitize?

Plant pollen is one of the main sources of allergens causing allergic diseases such as allergic rhinitis and asthma. Several allergens in plant pollen are panallergens which are also present in other allergen sources. As a result, sensitized individuals may also experience food allergies. The mechanism of sensitization and development of allergic inflammation is a consequence of the interaction of allergens with a large number of molecular factors that often are acting in a complex with other compounds, for example low-molecular-mass ligands, which contribute to the induction a type 2-driven response of immune system. In this review, special attention is paid not only to properties of allergens but also to an important role of their interaction with lipids and other hydrophobic molecules in pollen sensitization. The reactions of epithelial cells lining the nasal and bronchial mucosa and of other immunocompetent cells will also be considered, in particular the mechanisms of the activation of B and T lymphocytes and the formation of allergen-specific antibody responses.

A Novel Proline-Rich Cathelicidin from the Alpaca Vicugna pacos with Potency to Combat Antibiotic-Resistant Bacteria: Mechanism of Action and the Functional Role of the C-Terminal Region

Over recent years, a growing number of bacterial species have become resistant to clinically relevant antibiotics. Proline-rich antimicrobial peptides (PrAMPs) having a potent antimicrobial activity and a negligible toxicity toward mammalian cells attract attention as new templates for the development of antibiotic drugs. Here, we mined genomes of all living Camelidae species and found a novel family of Bac7-like proline-rich cathelicidins which inhibited bacterial protein synthesis. The N-terminal region of a novel peptide from the alpaca Vicugna pacos named VicBac is responsible for inhibition of bacterial protein synthesis with an IC₅₀ value of 0.5 µM in the E. coli cell-free system whereas the C-terminal region allows the peptide to penetrate bacterial membranes effectively. We also found that the full-length VicBac did not induce bacterial resistance after a two-week selection experiment, unlike the N-terminal truncated analog, which depended on the SbmA transport system. Both pro- and anti-inflammatory action of VicBac and its N-terminal truncated variant on various human cell types was found by multiplex immunoassay. The presence of the C-terminal tail in the natural VicBac does not provide for specific immune-modulatory effects in vitro but enhances the observed impact compared with the truncated analog. The pronounced antibacterial activity of VicBac, along with its moderate adverse effects on mammalian cells, make this molecule a promising scaffold for the development of peptide antibiotics.

Do Lipids Influence Gastrointestinal Processing: A Case Study of Major Soybean Allergen Gly m 4

Previously, we have demonstrated that Gly m 4, one of the major soybean allergens, could pass through the Caco-2 epithelial barrier and have proposed a mechanism of sensitization. However, it is not known yet whether Gly m 4 can reach the intestine in its intact form after digestion in stomach. In the present work, we studied an influence of various factors including lipids (fatty acids and lysolipids) on digestibility of Gly m 4. Using fluorescent and CD spectroscopies, we showed that Gly m 4 interacted with oleic acid and LPPG (lyso-palmitoyl phosphatidylglycerol), but its binding affinity greatly decreased under acidic conditions, probably due to the protein denaturation. The mimicking of gastric digestion revealed that Gly m 4 digestibility could be significantly reduced with the change of pH value and pepsin-to-allergen ratio, as well as by the presence of LPPG. We suggested that the protective effect of LPPG was unlikely associated with the allergen binding, but rather connected to the pepsin inhibition due to the lipid interaction with its catalytic site. As a result, we assumed that, under certain conditions, the intact Gly m 4 might be able to reach the human intestine and thereby could be responsible for allergic sensitization.

Dodecapeptide Cathelicidins of Cetartiodactyla: Structure, Mechanism of Antimicrobial Action, and Synergistic Interaction With Other Cathelicidins

In this study, dodecapeptide cathelicidins were shown to be widespread antimicrobial peptides among the Cetruminantia clade. In particular, we investigated the dodecapeptide from the domestic goat Capra hircus, designated as ChDode and its unique ortholog from the sperm whale Physeter catodon (PcDode). ChDode contains two cysteine residues, while PcDode consists of two dodecapeptide building blocks and contains four cysteine residues. The recombinant analogs of the peptides were obtained by heterologous expression in Escherichia coli cells. The structures of the peptides were studied by circular dichroism (CD), FTIR, and NMR spectroscopy. It was demonstrated that PcDode adopts a β-hairpin structure in water and resembles β-hairpin antimicrobial peptides, while ChDode forms a β-structural antiparallel covalent dimer, stabilized by two intermonomer disulfide bonds. Both peptides reveal a significant right-handed twist about 200 degrees per 8 residues. In DPC micelles ChDode forms flat β-structural tetramers by antiparallel non-covalent association of the dimers. The tetramers incorporate into the micelles in transmembrane orientation. Incorporation into the micelles and dimerization significantly diminished the amplitude of backbone motions of ChDode at the picosecond-nanosecond timescale. When interacting with negatively charged membranes containing phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), the ChDode peptide adopted similar oligomeric structure and was capable to form ion-conducting pores without membrane lysis. Despite modest antibacterial activity of ChDode, a considerable synergistic effect of this peptide in combination with another goat cathelicidin – the α-helical peptide ChMAP-28 was observed. This effect is based on an increase in permeability of bacterial membranes. In turn, this mechanism can lead to an increase in the efficiency of the combined action of the synergistic pair ChMAP-28 with the Pro-rich peptide mini-ChBac7.5Nα targeting the bacterial ribosome.

Investigation of Sensitization Potential of the Soybean Allergen Gly m 4 by Using Caco-2/Immune Cells Co-Culture Model

The soybean allergen Gly m 4 is known to cause severe allergic reactions including anaphylaxis, unlike other Bet v 1 homologues, which induce mainly local allergic reactions. In the present study, we aimed to investigate whether the food Bet v 1 homologue Gly m 4 can be a sensitizer of the immune system. Susceptibility to gastrointestinal digestion was assessed in vitro. Transport through intestinal epithelium was estimated using the Caco-2 monolayer. Cytokine response of different immunocompetent cells was evaluated by using Caco-2/Immune cells co-culture model. Absolute levels of 48 cytokines were measured by multiplex xMAP technology. It was shown that Gly m 4 can cross the epithelial barrier with a moderate rate and then induce production of IL-4 by mature dendritic cells in vitro. Although Gly m 4 was shown to be susceptible to gastrointestinal enzymes, some of its proteolytic fragments can selectively cross the epithelial barrier and induce production of Th2-polarizing IL-5, IL-10, and IL-13, which may point at the presence of the T-cell epitope among the crossed fragments. Our current data indicate that Gly m 4 can potentially be a sensitizer of the immune system, and intercommunication between immunocompetent and epithelial cells may play a key role in the sensitization process.

Identification of Na+-Pumping Cytochrome Oxidase in the Membranes of Extremely Alkaliphilic Thioalkalivibrio Bacteria

For the first time, the functioning of the oxygen reductase Na+-pump (Na+-pumping cytochrome c oxidase of the cbb₃-type) was demonstrated by examining the respiratory chain of the extremely alkaliphilic bacterium Thioalkalivibrio versutus [Muntyan, M. S., et al. (2015) Cytochrome cbb₃ of Thioalkalivibrio is a Na+-pumping cytochrome oxidase, Proc. Natl. Acad. Sci. USA, 112, 7695-7700], a product of the ccoNOQP operon. In this study, we detected and identified this enzyme using rabbit polyclonal antibody against the predicted C-terminal amino acid sequence of its catalytic subunit. We found that this cbb₃-type oxidase is synthesized in bacterial cells, where it is located in the membranes. The 48-kDa oxidase subunit (CcoN) is catalytic, while subunits CcoO and CcoP with molecular masses of 29 and 34 kDa, respectively, are cytochromes c. The theoretical pI values of the CcoN, CcoO, and CcoP subunits were determined. It was shown that parts of the CcoO and CcoP subunits exposed to the aqueous phase on the cytoplasmic membrane P-side are enriched with negatively charged amino acid residues, in contrast to the parts of the integral subunit CcoN adjacent to the aqueous phase. Thus, the Na+-pumping cytochrome c oxidase of T. versutus, both in function and in structure, demonstrates adaptation to extremely alkaline conditions.

Impact of Different Lipid Ligands on the Stability and IgE-Binding Capacity of the Lentil Allergen Len c 3

Previously, we isolated the lentil allergen Len c 3, belonging to the class of lipid transfer proteins, cross-reacting with the major peach allergen Pru p 3 and binding lipid ligands. In this work, the allergenic capacity of Len c 3 and effects of different lipid ligands on the protein stability and IgE-binding capacity were investigated. Impacts of pH and heat treating on ligand binding with Len c 3 were also studied. It was shown that the recombinant Len c 3 (rLen c 3) IgE-binding capacity is sensitive to heating and simulating of gastroduodenal digestion. While being heated or digested, the protein showed a considerably lower capacity to bind specific IgE in sera of allergic patients. The presence of lipid ligands increased the thermostability and resistance of rLen c 3 to digestion, but the level of these effects was dependent upon the ligand's nature. The anionic lysolipid LPPG showed the most pronounced protective effect which correlated well with experimental data on ligand binding. Thus, the Len c 3 stability and allergenic capacity can be retained in the conditions of food heat cooking and gastroduodenal digestion due to the presence of certain lipid ligands.

Antimicrobial Peptide Arenicin-1 Derivative Ar-1-(C/A) as Complement System Modulator

Antimicrobial peptides (AMPs) are not only cytotoxic towards host pathogens or cancer cells but also are able to act as immunomodulators. It was shown that some human and non-human AMPs can interact with complement proteins and thereby modulate complement activity. Thus, AMPs could be considered as the base for complement-targeted therapeutics development. Arenicins from the sea polychaete Arenicola marina, the classical example of peptides with a β-hairpin structure stabilized by a disulfide bond, were shown earlier to be among the most prospective regulators. Here, we investigate the link between arenicins' structure and their antimicrobial, hemolytic and complement-modulating activities using the derivative Ar-1-(C/A) without a disulfide bond. Despite the absence of this bond, the peptide retains all important functional activities and also appears less hemolytic in comparison with the natural forms. These findings could help to investigate new complement drugs for regulation using arenicin derivatives.

Structure Elucidation and Functional Studies of a Novel β-hairpin Antimicrobial Peptide from the Marine Polychaeta Capitella teleta

Endogenous antimicrobial peptides (AMPs) are evolutionary ancient molecular factors of innate immunity that play a key role in host defense. Among the most active and stable under physiological conditions AMPs are the peptides of animal origin that adopt a β-hairpin conformation stabilized by disulfide bridges. In this study, a novel BRICHOS-domain related AMP from the marine polychaeta Capitella teleta, named capitellacin, was produced as the recombinant analogue and investigated. The mature capitellacin exhibits high homology with the known β-hairpin AMP family—tachyplesins and polyphemusins from the horseshoe crabs. The β-hairpin structure of the recombinant capitellacin was proved by CD and NMR spectroscopy. In aqueous solution the peptide exists as monomeric right-handed twisted β-hairpin and its structure does not reveal significant amphipathicity. Moreover, the peptide retains this conformation in membrane environment and incorporates into lipid bilayer. Capitellacin exhibits a strong antimicrobial activity in vitro against a wide panel of bacteria including extensively drug-resistant strains. In contrast to other known β-hairpin AMPs, this peptide acts apparently via non-lytic mechanism at concentrations inhibiting bacterial growth. The molecular mechanism of the peptide antimicrobial action does not seem to be related to the inhibition of bacterial translation therefore other molecular targets may be assumed. The reduced cytotoxicity against human cells and high antibacterial cell selectivity as compared to tachyplesin-1 make it an attractive candidate compound for an anti-infective drug design.

Caprine Bactenecins as Promising Tools for Developing New Antimicrobial and Antitumor Drugs

Proline-rich antimicrobial peptides (PR-AMPs) having a potent antimicrobial activity predominantly toward Gram-negative bacteria and negligible toxicity toward host cells, are attracting attention as new templates for developing antibiotic drugs. We have previously isolated and characterized several bactenecins that are promising in this respect, from the leukocytes of the domestic goat Capra hircus: ChBac5, miniChBac7.5N-α, and -β, as well as ChBac3.4. Unlike the others, ChBac3.4 shows a somewhat unusual pattern of activities for a mammalian PR-AMP: it is more active against bacterial membranes as well as tumor and, to the lesser extent, normal cells. Here we describe a SAR study of ChBac3.4 (RFRLPFRRPPIRIHPPPFYPPFRRFL-NH2) which elucidates its peculiarities and evaluates its potential as a lead for antimicrobial or anticancer drugs based on this peptide. A set of designed structural analogues of ChBac3.4 was explored for antibacterial activity toward drug-resistant clinical isolates and antitumor properties. The N-terminal region was found to be important for the antimicrobial action, but not responsible for the toxicity toward mammalian cells. A shortened variant with the best selectivity index toward bacteria demonstrated a pronounced synergy in combination with antibiotics against Gram-negative strains, albeit with a somewhat reduced ability to inhibit biofilm formation compared to native peptide. C-terminal amidation was examined for some analogues, which did not affect antimicrobial activity, but somewhat altered the cytotoxicity toward host cells. Interestingly, non-amidated peptides showed a slight delay in their impact on bacterial membrane integrity. Peptides with enhanced hydrophobicity showed increased toxicity, but in most cases their selectivity toward tumor cells also improved. While most analogues lacked hemolytic properties, a ChBac3.4 variant with two additional tryptophan residues demonstrated an appreciable activity toward human erythrocytes. The variant demonstrating the best tumor/nontumor cell selectivity was found to more actively initiate apoptosis in target cells, though its action was slower than that of the native ChBac3.4. Its antitumor effectiveness was successfully verified in vivo in a murine Ehrlich ascites carcinoma model. The obtained results demonstrate the potential of structural modification to manage caprine bactenecins’ selectivity and activity spectrum and confirm that they are promising prototypes for antimicrobial and anticancer drugs design.

New insights into ligand binding by plant lipid transfer proteins: A case study of the lentil Lc-LTP2

Lipid transfer proteins (LTPs) are an important class of plant proteins containing an internal cavity and binding hydrophobic ligands. Although LTP structures and functions are well studied, mechanisms of ligand binding remain unclear. Earlier, we discovered the lentil lipid transfer protein Lc-LTP2 capable of binding and transfer various ligands. We have shown that the "bottom" entrance of the Lc-LTP2 cavity takes part in attachment to the micelle surface and in lipids uptake. Here, we studied the role of Arg45 and Tyr80, located at the "bottom" entrance, in Lc-LTP2 ligand binding. We obtained recombinant mutant analogs of Lc-LTP2 (R45A, Y80A, R45A/Y80A), investigated their ability to bind fatty acids and lysolipids, as well as performed molecular modeling of the protein-ligand complexes. We showed that replacement of one or both residues led to a change of the internal hydrophobic cavity dimensions. As a result, lipids may change their orientation into the protein cavity, and thereby binding ability of mutant analogs may be affected as well. In the present work, we revealed an important role of Arg45 and Tyr80 in stabilization of the Lc-LTP2 complexes with both fatty acids and lysolipids with different ligand orientation.

Role of Pea LTPs and Abscisic Acid in Salt-Stressed Roots

Lipid transfer proteins (LTPs) are a class of small, cationic proteins that bind and transfer lipids and play an important role in plant defense. However, their precise biological role in plants under adverse conditions including salinity and possible regulation by stress hormone abscisic acid (ABA) remains unknown. In this work, we studied the localization of LTPs and ABA in the roots of pea plants using specific antibodies. Presence of LTPs was detected on the periphery of the cells mainly located in the phloem. Mild salt stress (50 mM NaCI) led to slowing plant growth and higher immunostaining for LTPs in the phloem. The deposition of suberin in Casparian bands located in the endoderma revealed with Sudan III was shown to be more intensive under salt stress and coincided with the increased LTP staining. All obtained data suggest possible functions of LTPs in pea roots. We assume that these proteins can participate in stress-induced pea root suberization or in transport of phloem lipid molecules. Salt stress increased ABA immunostaining in pea root cells but its localization was different from that of the LTPs. Thus, we failed to confirm the hypothesis regarding the direct influence of ABA on the level of LTPs in the salt-stressed root cells.

Pediocin-Like Antimicrobial Peptides of Bacteria

Bacteriocins are bacterial antimicrobial peptides that, unlike classical peptide antibiotics, are products of ribosomal synthesis and usually have a narrow spectrum of antibacterial activity against species closely related to the producers. Pediocin-like bacteriocins (PLBs) belong to the class IIa of the bacteriocins of Gram-positive bacteria. PLBs possess high activity against pathogenic bacteria from Listeria and Enterococcus genera. Molecular target for PLBs is a membrane protein complex - bacterial mannose-phosphotransferase. PLBs can be synthesized by components of symbiotic microflora and participate in the maintenance of homeostasis in various compartments of the digestive tract and on the surface of epithelial tissues contacting the external environment. PLBs could give a rise to a new group of antibiotics of narrow spectrum of activity.

Biotechnological Method of Preparation and Characterization of Recombinant Antimicrobial Peptide Avicin A from Enterococcus avium

Avicin A is a bacteriocin from the gram-positive bacterium Enterococcus avium. It exhibits a high microbicidal activity against bacteria of the genus Listeria, a causative agent of the severe human infection listeriosis. We developed a biotechnological method for obtaining avicin A and characterized its structure and biological activity. We also proposed a possible mechanism of the antimicrobial action of avicin A.

Anticancer Activity of the Goat Antimicrobial Peptide ChMAP-28

Cytotoxic effect of the antimicrobial peptide ChMAP-28 from leucocytes of the goat Capra hircus was examined against five cancer and two normal human cell lines. ChMAP-28 has the amino acid sequence GRFKRFRKKLKRLWHKVGPFVGPILHY and is homologous to other α-helical mammalian antimicrobial peptides. ChMAP-28 shows considerably higher cytotoxicity against cultured tumor cells than toward normal cells at concentrations of <10 μM. Our findings suggest that ChMAP-28 can initiate necrotic death of cancer cells. Its cytotoxic effect is accomplished due to disruption of the plasma membrane integrity and is not abrogated by the addition of the caspase inhibitor Z-VAD-FMK. ChMAP-28 causes permeabilization of cytoplasmic membrane of human leukemia cells HL-60 already after 15 min of incubation. Here, we show that ChMAP-28 has one of the highest antitumor activity in vitro among all known antimicrobial peptides. We speculate that the observed specificity of ChMAP-28 cytotoxic effect against tumor cells is due to its relatively low hydrophobicity and high cationicity. In the meantime, this peptide has low hemolytic activity, which generates a potential for its use as a therapeutic agent.

Combined Antibacterial Effects of Goat Cathelicidins With Different Mechanisms of Action

Being essential components of innate immune system, animal antimicrobial peptides (AMPs) also known as host-defense peptides came into sharp focus as possible alternatives to conventional antibiotics due to their high efficacy against a broad range of MDR pathogens and low rate of resistance development. Mammalian species can produce a set of co-localized AMPs with different structures and mechanisms of actions. Here we examined the combined antibacterial effects of cathelicidins, structurally diverse family of host-defense peptides found in vertebrate species. As a model we have used structurally distinct cathelicidins expressed in the leukocytes of goat Capra hircus. The recombinant analogs of natural peptides were obtained by heterologous expression in bacterial system and biological activities as well as the major mechanisms of antibacterial action of the peptides were investigated. As the result, the marked synergistic effect against wide panel of bacterial strains including extensively drug-resistant ones was observed for the pair of membranolytic α-helical amphipathic peptide ChMAP-28 and Pro-rich peptide mini-ChBac7.5Nα targeting a bacterial ribosome. ChMAP-28 was shown to damage the outer bacterial membrane at sub-inhibitory concentrations that could facilitate Pro-rich peptide translocation into the cell. Finally, resistance changes under a long-term continuous selective pressure of each individual peptide and the synergistic combination of both peptides were tested against Escherichia coli strains. The combination was shown to keep a high activity after the 26-days selection experiment in contrast to mini-ChBac7.5Nα used alone and the reference antibiotic polymyxin B. We identified the point mutation leading to amino acid substitution V102E in the membrane transport protein SbmA of the mini-ChBac7.5Nα-resistant strain obtained by selection. The experiments revealed that the presence of sub-inhibitory concentrations of ChMAP-28 restored the activity of mini-ChBac7.5Nα against this strain and clinical isolate with a weak sensitivity to mini-ChBac7.5Nα. The obtained results suggest a potential medical application of synergistic combinations of natural cathelicidins, which allows using a lower therapeutic dose and minimizes the risk of resistance development.

Cytotoxic Potential of the Novel Horseshoe Crab Peptide Polyphemusin III

Biological activity of the new antimicrobial peptide polyphemusin III from the horseshoe crab Limulus polyphemus was examined against bacterial strains and human cancer, transformed, and normal cell cultures. Polyphemusin III has the amino acid sequence RRGCFRVCYRGFCFQRCR and is homologous to other β-hairpin peptides from the horseshoe crab. Antimicrobial activity of the peptide was evaluated and MIC (minimal inhibitory concentration) values were determined. IC₅₀ (half-maximal inhibitory concentration) values measured toward human cells revealed that polyphemusin III showed a potent cytotoxic activity at concentrations of <10 μM. Polyphemusin III caused fast permeabilization of the cytoplasmic membrane of human leukemia cells HL-60, which was measured with trypan blue exclusion assay and lactate dehydrogenase-release assay. Flow cytometry experiments for annexin V-FITC/ propidium iodide double staining revealed that the caspase inhibitor, Z-VAD-FMK, did not abrogate disruption of the plasma membrane by polyphemusin III. Our data suggest that polyphemusin III disrupts the plasma membrane integrity and induces cell death that is apparently not related to apoptosis. In comparison to known polyphemusins and tachyplesins, polyphemusin III demonstrates a similar or lower antimicrobial effect, but significantly higher cytotoxicity against human cancer and transformed cells in vitro.

In Vitro Study of Antitumor Effect of Antimicrobial Peptide Tachyplesin I in Combination with Cisplatin

We studied combined effect of β-hairpin antimicrobial peptide tachyplesin I and cytotoxic agent cisplatin on tumor and normal human cell lines. MTT assay and flow cytometry showed that tachyplesin I selectively sensitized cancer cells to cisplatin in specified concentration ratios. In vitro experiments demonstrated that combined use of tachyplesin I and cisplatin allows decreasing the effective dose of the cytostatic thus reducing nonspecific toxicity.

The First Recombinant Viper Three-Finger Toxins: Inhibition of Muscle and Neuronal Nicotinic Acetylcholine Receptors

Genes encoding two three-finger toxins TFT-AF and TFT-VN, nucleotide sequences of which were earlier determined by cloning cDNA from venom glands of vipers Azemiops feae and Vipera nikolskii, respectively, were expressed for the first time in E. coli cells. The biological activity of these toxins was studied by electrophysiological techniques, calcium imaging, and radioligand analysis. It was shown for the first time that viper three-finger toxins are antagonists of nicotinic acetylcholine receptors of neuronal and muscle type.

Marine antimicrobial peptide arenicin adopts a monomeric twisted β-hairpin structure and forms low conductivity pores in zwitterionic lipid bilayers

Arenicins are 21-residue β-hairpin antimicrobial peptides (AMPs) isolated from the marine lugworm Arenicola marina [Ovchinnikova et al., FEBS Lett. 2004;577:209-214]. The peptides have a high positive charge (+6) and display a broad spectrum of antimicrobial activities against bacteria and fungi. Arenicins adopt the monomeric highly twisted β-hairpin in water or planar β-structural dimers in anionic liposomes and detergent micelles. Until now, the interaction of cationic β-structural AMPs with zwitterionic phospholipid bilayers mimicking eukaryotic membranes is not well understood. To study the structural basis of arenicins activity against eukaryotic cells, we investigated arenicin-2 in the solvents of low polarity (ethanol, 4% dioxane) and in zwitterionic soybean PC and PC/PE liposomes by CD and FTIR spectroscopy. It was shown that arenicin-2 adopted the twisted β-hairpin structure in all the environments studied. Measurements of the Trp fluorescence and H→D exchange in soybean PC liposomes and boundary potential in the planar DPhPC bilayers confirmed the partitioning of the arenicin-2 monomers into interfacial region of the zwitterionic membranes. The low-conductivity (0.12 nS) arenicin-2 pores were detected in the DPhPC bilayers. The lifetime of the open state (up to 260 ms) was significantly longer than lifetime of low-conductivity (0.23 nS) pores previously described in partially anionic membranes (44 ms). The formation of narrow arenicin-2 pores without disruption of the membrane was discussed in the light of the disordered toroidal pore model previously proposed for β-structural AMPs [Jean - Francois et al. Biophys. J. 2008;95:5748 - 5756]. A novel non-lytic mechanism of the arenicin-2 action was proposed.

Comparative in vitro study on cytotoxicity of recombinant β-hairpin peptides

Natural antimicrobial peptides (AMPs) are important components of the innate immune system with a wide spectrum of biological activity. In this study, we investigated the cytotoxic effect of three recombinant β-hairpin cationic AMPs: arenicin-1 from the polychaeta Arenicola marina, tachyplesin I from the horseshoe crab Tachypleus tridentatus, and gomesin from the spider Acanthoscurria gomesiana. All the three β-hairpin AMPs were overexpressed in Escherichia coli. Different cell lines were incubated with various concentrations of the investigated AMPs in order to evaluate their cytotoxic activity. Double staining with subsequent flow cytometric analysis was used to determine the predominant way of cell death mediated by each AMP. Hemolytic activity of the peptides was tested against fresh human red blood cells. Our results indicated that all the three AMPs exhibited significant cytotoxic effect against cancer cells that varied depending on the cell line type and, in most cases, on the presence of serum components. Flow cytometric analysis implicitly indicated that tachyplesin I mostly promoted late apoptosis/necrosis, while arenicin-1 and gomesin induced early apoptosis under the same conditions. Tachyplesin I proved to be the most promising therapeutic candidate as it displayed the highest specific cytotoxicity against cancer cell lines, independent of the serum presence.

Plant Pathogenesis-Related Proteins PR-10 and PR-14 as Components of Innate Immunity System and Ubiquitous Allergens

Pathogenesis-related (PR) proteins are components of innate immunity system in plants. They play an important role in plant defense against pathogens. Lipid transfer proteins (LTPs) and Bet v 1 homologs comprise of two separate families of PR-proteins. Both LTPs (PR-14) and Bet v 1 homologs (PR-10) are multifunctional small proteins involving in plant response to abiotic and biotic stress conditions. The representatives of these PR-protein families do not show any sequence similarity but have other common biochemical features such as low molecular masses, the presence of hydrophobic cavities, ligand binding properties, and antimicrobial activities. Besides, many members of PR-10 and PR-14 families are ubiquitous plant panallergens which are able to cause sensitization of human immune system and crossreactive allergic reactions to plant food and pollen. This review is aimed at comparative analysis of structure-functional and allergenic properties of the PR-10 and PR-14 families, as well as prospects for their medicinal application.

Comparative in vitro study on cytotoxicity of recombinant β-hairpin peptides

Natural antimicrobial peptides (AMPs) are important components of the innate immune system with a wide spectrum of biological activity. In this study, we investigated the cytotoxic effect of three recombinant β-hairpin cationic AMPs: arenicin-1 from the polychaeta Arenicola marina, tachyplesin I from the horseshoe crab Tachypleus tridentatus, and gomesin from the spider Acanthoscurria gomesiana. All the three β-hairpin AMPs were overexpressed in Escherichia coli. Different cell lines were incubated with various concentrations of the investigated AMPs in order to evaluate their cytotoxic activity. Double staining with subsequent flow cytometric analysis was used to determine the predominant way of cell death mediated by each AMP. Hemolytic activity of the peptides was tested against fresh human red blood cells. Our results indicated that all the three AMPs exhibited significant cytotoxic effect against cancer cells that varied depending on the cell line type and, in most cases, on the presence of serum components. Flow cytometric analysis implicitly indicated that tachyplesin I mostly promoted late apoptosis/necrosis, while arenicin-1 and gomesin induced early apoptosis under the same conditions. Tachyplesin I proved to be the most promising therapeutic candidate as it displayed the highest specific cytotoxicity against cancer cell lines, independent of the serum presence.

Dimerization of the antimicrobial peptide arenicin plays a key role in the cytotoxicity but not in the antibacterial activity

The β-hairpin antimicrobial peptides arenicins from marine polychaeta Arenicola marina exhibit a broad spectrum of antimicrobial activity and high cytotoxicity. In this study the biological activities of arenicin-1 and its therapeutically valuable analog Ar-1[V8R] were investigated. The peptide Ar-1[V8R] displays significantly reduced cytotoxicity against mammalian cells relative to the wild-type arenicin-1. At the same time, both peptides exhibit similar antibacterial activities and kinetics of bacterial membrane permeabilization. Comparative NMR analysis of the peptides spatial structures in water and membrane-mimicking environment showed that Ar-1[V8R] in contrast to arenicin has significantly lower dimerization propensity. Thus, dimerization of the antimicrobial peptide arenicin plays a key role in the cytotoxicity but not in the antibacterial activity.

[Interaction of Arenicin-1 with C1q Protein]

The interaction between arenicin-1, that is an antimicrobial peptide from polychaeta Arenicola marina, and human complement system protein C1q was studied using enzyme-linked receptor sorbent assay and ELISA. We revealed that arenicin-1 and C1q form complex that is stable in high ionic strength condition 0.5 M NaCl. The ability of C1q to interact with arenicin-1 is comparable with the binding activity of C1q towards another antimicrobial peptide, porcine cathelicidin protegrin-1, which has a similar spatial arrangement with arenicin-1. Namely, both arenicin-1 and protegrin-1 form cystine-stabilized antiparallel β-hairpin structure.

A novel lipid transfer protein from the pea Pisum sativum: isolation, recombinant expression, solution structure, antifungal activity, lipid binding, and allergenic properties

BACKGROUND

Plant lipid transfer proteins (LTPs) assemble a family of small (7-9 kDa) ubiquitous cationic proteins with an ability to bind and transport lipids as well as participate in various physiological processes including defense against phytopathogens. They also form one of the most clinically relevant classes of plant allergens. Nothing is known to date about correlation between lipid-binding and IgE-binding properties of LTPs. The garden pea Pisum sativum is widely consumed crop and important allergenic specie of the legume family. This work is aimed at isolation of a novel LTP from pea seeds and characterization of its structural, functional, and allergenic properties.

RESULTS

Three novel lipid transfer proteins, designated as Ps-LTP1-3, were found in the garden pea Pisum sativum, their cDNA sequences were determined, and mRNA expression levels of all the three proteins were measured at different pea organs. Ps-LTP1 was isolated for the first time from the pea seeds, and its complete amino acid sequence was determined. The protein exhibits antifungal activity and is a membrane-active compound that causes a leakage from artificial liposomes. The protein binds various lipids including bioactive jasmonic acid. Spatial structure of the recombinant uniformly (13)C,(15)N-labelled Ps-LTP1 was solved by heteronuclear NMR spectroscopy. In solution the unliganded protein represents the mixture of two conformers (relative populations ~ 85:15) which are interconnected by exchange process with characteristic time ~ 100 ms. Hydrophobic residues of major conformer form a relatively large internal tunnel-like lipid-binding cavity (van der Waals volume comes up to ~1000 Å(3)). The minor conformer probably corresponds to the protein with the partially collapsed internal cavity.

CONCLUSIONS

For the first time conformational heterogeneity in solution was shown for an unliganded plant lipid transfer protein. Heat denaturation profile and simulated gastrointestinal digestion assay showed that Ps-LTP1 displayed a high thermal and digestive proteolytic resistance proper for food allergens. The reported structural and immunological findings seem to describe Ps-LTP1 as potential cross-reactive allergen in LTP-sensitized patients, mostly Pru p 3(+) ones. Similarly to allergenic LTPs the potential IgE-binding epitope of Ps-LTP1 is located near the proposed entrance into internal cavity and could be involved in lipid-binding.

Effective lipid-detergent system for study of membrane active peptides in fluid liposomes

The structure of peptide antibiotic gramicidin A (gA) was studied in phosphatidylcholin liposomes modified by nonionic detergent Triton X-100. First, the detergent : lipid ratio at which the saturation of lipid membrane by Triton X-100 occurs (Re (sat)), was determined by light scattering. Measurements of steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene at sublytic concentrations of detergent showed that after saturation of the membrane by Triton X-100 microviscosity of lipid bilayer is reduced by 20%. The equilibrium conformational state of gA in phosphatidylcholine liposomes at Re (sat) was studied by CD spectroscopy. It was found that the conformational state of this channel-forming peptide changed crucially when Triton X-100 induced transition to more fluid membranes. The gA single-channel measurements were made with Triton X-100 containing bilayers. Tentative assignment of the channel type and gA structures was made by correlation of CD data with conductance histograms. Lipid-detergent system with variable viscosity developed in this work can be used to study the structure and folding of other membrane-active peptides.

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

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

Bioengineering and functional characterization of arenicin shortened analogs with enhanced antibacterial activity and cell selectivity

New bioengineering approaches are required for development of more active and less toxic antimicrobial peptides. In this study we used β-hairpin antimicrobial peptide arenicin-1 as a template for design of more potent antimicrobials. In particular, six shortened 17-residue analogs were obtained by recombinant expression in Escherichia coli. Besides, we have introduced the second disulfide bridge by analogy with the structure of tachyplesins. As a result, a number of analogs with enhanced activity and cell selectivity were developed. In comparison with arenicin-1, which acts on cell membranes with low selectivity, the most potent and promising its analog termed ALP1 possessed two-fold higher antibacterial activity and did not affect viability of mammalian cells at concentration up to 50 μM. The therapeutic index of ALP1 against both Gram-positive and Gram-negative bacteria was significantly increased compared with that of arenicin-1 while the mechanism of action remained the same. Like arenicin-1, the analog rapidly disrupt membranes of both stationary and exponential phase bacterial cells and effectively kills multidrug-resistant Gram-negative bacteria. Furthermore, ALP1 was shown to bind DNA in vitro at a ratio of 1:1 (w/w). The circular dichroism spectra demonstrated that secondary structures of the shortened analogs were similar to that of arenicin-1 in water solution, but significantly differed in membrane-mimicking environments. This work shows that a strand length is one of the key parameters affecting cell selectivity of β-hairpin antimicrobial peptides.

A novel lipid transfer protein from the dill Anethum graveolens L.: isolation, structure, heterologous expression, and functional characteristics

A novel lipid transfer protein, designated as Ag-LTP, was isolated from aerial parts of the dill Anethum graveolens L. Structural, antimicrobial, and lipid binding properties of the protein were studied. Complete amino acid sequence of Ag-LTP was determined. The protein has molecular mass of 9524.4 Da, consists of 93 amino acid residues including eight cysteines forming four disulfide bonds. The recombinant Ag-LTP was overexpressed in Escherichia coli and purified. NMR investigation shows that the Ag-LTP spatial structure contains four α-helices, forming the internal hydrophobic cavity, and a long C-terminal tail. The measured volume of the Ag-LTP hydrophobic cavity is equal to ~800 A(3), which is much larger than those of other plant LTP1s. Ag-LTP has weak antifungal activity and unpronounced lipid binding specificity but effectively binds plant hormone jasmonic acid. Our results afford further molecular insight into biological functions of LTP in plants.