Pn-AMP1, a plant defense protein, induces actin depolarization in yeasts

Candida albicans and Antifungal Peptides

Candida albicans, a ubiquitous opportunistic fungal pathogen, plays a pivotal role in human health and disease. As a commensal organism, it normally resides harmlessly within the human microbiota. However, under certain conditions, C. albicans can transition into a pathogenic state, leading to various infections collectively known as candidiasis. With the increasing prevalence of immunocompromised individuals and the widespread use of invasive medical procedures, candidiasis has become a significant public health concern. The emergence of drug-resistant strains further complicates treatment options, highlighting the urgent need for alternative therapeutic strategies. Antifungal peptides (AFPs) have gained considerable attention as potential candidates for combating Candida spp. infections. These naturally occurring peptides possess broad-spectrum antimicrobial activity, including specific efficacy against C. albicans. AFPs exhibit several advantageous properties, such as rapid killing kinetics, low propensity for resistance development, and diverse mechanisms of action, making them promising alternatives to conventional antifungal agents. In recent years, extensive research has focused on discovering and developing novel AFPs with improved efficacy and selectivity against Candida species. Advances in biotechnology and synthetic peptide design have enabled the modification and optimization of natural peptides, enhancing their stability, bioavailability, and therapeutic potential. Nevertheless, several challenges must be addressed before AFPs can be widely implemented in clinical practice. These include optimizing peptide stability, enhancing delivery methods, overcoming potential toxicity concerns, and conducting comprehensive preclinical and clinical studies. This commentary presents a short overview of candidemia and AFP; articles and reviews published in the last 10 years were searched on The National Library of Medicine (National Center for Biotechnology Information-NIH-PubMed). The terms used were C. albicans infections, antimicrobial peptides, antifungal peptides, antifungal peptides mechanisms of action, candidemia treatments and guidelines, synthetic peptides and their challenges, and antimicrobial peptides in clinical trials as the main ones. Older publications were cited if they brought some relevant concept or helped to bring a perspective into our narrative. Articles older than 20 years and those that appeared in PubMed but did not match our goal to bring updated information about using antifungal peptides as an alternative to C. albicans infections were not considered.

Plant Antimicrobial Peptides: Insights into Structure-Function Relationships for Practical Applications

Antimicrobial peptides (AMPs) are short polypeptide molecules produced by multicellular organisms that are involved in host defense and microbiome preservation. In recent years, AMPs have attracted attention as novel drug candidates. However, their successful use requires detailed knowledge of the mode of action and identification of the determinants of biological activity. In this review, we focused on structure-function relationships in the thionins, α-hairpinins, hevein-like peptides, and the unique Ib-AMP peptides isolated from Impatiens balsamina. We summarized the available data on the amino acid sequences and 3D structure of peptides, their biosynthesis, and their biological activity. Special attention was paid to the determination of residues that play a key role in the activity and the identification of the minimal active cores. We have shown that even subtle changes in amino acid sequences can affect the biological activity of AMPs, which opens up the possibility of creating molecules with improved properties, better therapeutic efficacy, and cheaper large-scale production.

Short Peptides Make a Big Difference: The Role of Botany-Derived AMPs in Disease Control and Protection of Human Health

Botany-derived antimicrobial peptides (BAMPs), a class of small, cysteine-rich peptides produced in plants, are an important component of the plant immune system. Both in vivo and in vitro experiments have demonstrated their powerful antimicrobial activity. Besides in plants, BAMPs have cross-kingdom applications in human health, with toxic and/or inhibitory effects against a variety of tumor cells and viruses. With their diverse molecular structures, broad-spectrum antimicrobial activity, multiple mechanisms of action, and low cytotoxicity, BAMPs provide ideal backbones for drug design, and are potential candidates for plant protection and disease treatment. Lots of original research has elucidated the properties and antimicrobial mechanisms of BAMPs, and characterized their surface receptors and in vivo targets in pathogens. In this paper, we review and introduce five kinds of representative BAMPs belonging to the pathogenesis-related protein family, dissect their antifungal, antiviral, and anticancer mechanisms, and forecast their prospects in agriculture and global human health. Through the deeper understanding of BAMPs, we provide novel insights for their applications in broad-spectrum and durable plant disease prevention and control, and an outlook on the use of BAMPs in anticancer and antiviral drug design.

Antimicrobial Resistance in ESKAPE Pathogens

Antimicrobial-resistant ESKAPE ( Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens represent a global threat to human health. The acquisition of antimicrobial resistance genes by ESKAPE pathogens has reduced the treatment options for serious infections, increased the burden of disease, and increased death rates due to treatment failure and requires a coordinated global response for antimicrobial resistance surveillance. This looming health threat has restimulated interest in the development of new antimicrobial therapies, has demanded the need for better patient care, and has facilitated heightened governance over stewardship practices.

The interaction Between Carbohydrates and the Antimicrobial Peptide P-113Tri is Involved in the Killing of Candida albicans

The emergence of drug resistance to Candida albicans is problematic in the clinical setting. Therefore, developing new antifungal drugs is in high demand. Our previous work indicated that the antimicrobial peptide P-113Tri exhibited higher antifungal activity against planktonic cells, biofilm cells, and clinical isolates of Candida species compared to its parental peptide P-113. In this study, we further investigated the difference between these two peptides in their mechanisms against C. albicans. Microscopic examination showed that P-113 rapidly gained access to C. albicans cells. However, most of the P-113Tri remained on the cell surface. Moreover, using a range of cell wall-defective mutants and competition assays, the results indicated that phosphomannan and N-linked mannan in the cell wall are important for peptide binding to C. albicans cells. Furthermore, the addition of exogenous phosphosugars reduced the efficacy of the peptide, suggesting that negatively charged phosphosugars also contributed to the peptide binding to the cell wall polysaccharides. Finally, using a glycan array, P-113Tri, but not P-113, can bind to other glycans commonly present on other microbial and mammalian cells. Together, these results suggest that P-113 and P-113Tri have fundamental differences in their interaction with C. albicans and candidacidal activities.

Antimicrobial Peptides - Small but Mighty Weapons for Plants to Fight Phytopathogens

Antimicrobial Peptides (AMPs) have diverse structures, varied modes of actions, and can inhibit the growth of a wide range of pathogens at low concentrations. Plants are constantly under attack by a wide range of phytopathogens causing massive yield losses worldwide. To combat these pathogens, nature has armed plants with a battery of defense responses including Antimicrobial Peptides (AMPs). These peptides form a vital component of the two-tier plant defense system. They are constitutively expressed as part of the pre-existing first line of defense against pathogen entry. When a pathogen overcomes this barrier, it faces the inducible defense system, which responds to specific molecular or effector patterns by launching an arsenal of defense responses including the production of AMPs. This review emphasizes the structural and functional aspects of different plant-derived AMPs, their homology with AMPs from other organisms, and how their biotechnological potential could generate durable resistance in a wide range of crops against different classes of phytopathogens in an environmentally friendly way without phenotypic cost.

The interaction with fungal cell wall polysaccharides determines the salt tolerance of antifungal plant defensins

The fungal cell wall is the first point of contact between fungal pathogens and host organisms. It serves as a protective barrier against biotic and abiotic stresses and as a signal to the host that a fungal pathogen is present. The fungal cell wall is made predominantly of carbohydrates and glycoproteins, many of which serve as binding receptors for host defence molecules or activate host immune responses through interactions with membrane-bound receptors. Plant defensins are a large family of cationic antifungal peptides that protect plants against fungal disease. Binding of the plant defensin NaD1 to the fungal cell wall has been described but the specific component of the cell wall with which this interaction occurred was unknown. The effect of binding was also unclear, that is whether the plant defensin used fungal cell wall components as a recognition motif for the plant to identify potential pathogens or if the cell wall acted to protect the fungus against the defensin. Here we describe the interaction between the fungal cell wall polysaccharides chitin and β-glucan with NaD1 and other plant defensins. We discovered that the β-glucan layer protects the fungus against plant defensins and the loss of activity experienced by many cationic antifungal peptides at elevated salt concentrations is due to sequestration by fungal cell wall polysaccharides. This has limited the development of cationic antifungal peptides for the treatment of systemic fungal diseases in humans as the level of salt in serum is enough to inactivate most cationic peptides.

The role of antimicrobial peptides in plant immunity

Selective pressure imposed by millions of years of relentless biological attack has led to the development of an extraordinary array of defense strategies in plants. Among these, antimicrobial peptides (AMPs) stand out as one of the most prominent components of the plant immune system. These small and usually basic peptides are deployed as a generalist defense strategy that grants direct and durable resistance against biotic stress. Even though their name implies a function against microbes, the range of plant-associated organisms affected by these peptides is much broader. In this review, we highlight the advances in our understanding on the role of AMPs in plant immunity. We demonstrate that the capacity of plant AMPs to act against a large spectrum of enemies relies on their diverse mechanism of action and remarkable structural stability. The efficacy of AMPs as a defense strategy is evidenced by their widespread occurrence in the plant kingdom, an astonishing heterogeneity in host peptide composition, and the extent to which plant enemies have evolved effective counter-measures to evade AMP action. Plant AMPs are becoming an important topic of research due to their significance in allowing plants to thrive and for their enormous potential in agronomical and pharmaceutical fields.

Hevein-Like Antimicrobial Peptides of Plants

Plant antimicrobial peptides represent one of the evolutionarily oldest innate immunity components providing the first line of host defense to pathogen attacks. This review is dedicated to a small, currently actively studied family of hevein-like peptides that can be found in various monocot and dicot plants. The review thoroughly describes all known peptides belonging to this family including data on their structures, functions, and antimicrobial activity. The main features allowing to assign these peptides to a separate family are given, and the specific characteristics of each peptide are described. Further, the mode of action for hevein-like peptides, their role in plant immune system, and the applications of these molecules in biotechnology and medicine are considered.

The in vitro, in vivo antifungal activity and the action mode of Jelleine-I against Candida species

Recently, the mortality of life-threatening fungal infections increased dramatically. However, there are few antifungals existed. Antimicrobial peptides (AMPs) as promising antifungal candidates have attracted much attention. Here, we present a small antimicrobial peptide Jelleine-I that had potent in vitro and in vivo antifungal activity. Negligible hemolytic activity and in vivo toxicity were observed. Selectivity index (SI) of Jelleine-I is at least 4.6 times higher than amphotericin B. Jelleine-I could increase the production of cellular ROS and bind with genome DNA. This may contribute to its antifungal activity. Furthermore, drug resistance is not induced when the fungal cells were repeatedly treated by Jelleine-I. In conclusion, our results suggest that Jelleine-I may have the potential to be developed as a novel antifungal agent.

New reference genome sequences of hot pepper reveal the massive evolution of plant disease-resistance genes by retroduplication

BACKGROUND

Transposable elements are major evolutionary forces which can cause new genome structure and species diversification. The role of transposable elements in the expansion of nucleotide-binding and leucine-rich-repeat proteins (NLRs), the major disease-resistance gene families, has been unexplored in plants.

RESULTS

We report two high-quality de novo genomes (Capsicum baccatum and C. chinense) and an improved reference genome (C. annuum) for peppers. Dynamic genome rearrangements involving translocations among chromosomes 3, 5, and 9 were detected in comparison between C. baccatum and the two other peppers. The amplification of athila LTR-retrotransposons, members of the gypsy superfamily, led to genome expansion in C. baccatum. In-depth genome-wide comparison of genes and repeats unveiled that the copy numbers of NLRs were greatly increased by LTR-retrotransposon-mediated retroduplication. Moreover, retroduplicated NLRs are abundant across the angiosperms and, in most cases, are lineage-specific.

CONCLUSIONS

Our study reveals that retroduplication has played key roles for the massive emergence of NLR genes including functional disease-resistance genes in pepper plants.

Potent in vitro and in vivo antifungal activity of a small molecule host defense peptide mimic through a membrane-active mechanism

Lethal systemic fungal infections of Candida species are increasingly common, especially in immune compromised patients. By in vitro screening of small molecule mimics of naturally occurring host defense peptides (HDP), we have identified several active antifungal molecules, which also exhibited potent activity in two mouse models of oral candidiasis. Here we show that one such compound, C4, exhibits a mechanism of action that is similar to the parent HDP upon which it was designed. Specifically, its initial interaction with the anionic microbial membrane is electrostatic, as its fungicidal activity is inhibited by cations. We observed rapid membrane permeabilization to propidium iodide and ATP efflux in response to C4. Unlike the antifungal peptide histatin 5, it did not require energy-dependent transport across the membrane. Rapid membrane disruption was observed by both fluorescence and electron microscopy. The compound was highly active in vitro against numerous fluconazole-resistant clinical isolates of C. albicans and non-albicans species, and it exhibited potent, dose-dependent activity in a mouse model of invasive candidiasis, reducing kidney burden by three logs after 24 hours, and preventing mortality for up to 17 days. Together the results support the development of this class of antifungal drug to treat invasive candidiasis.

Signaling pathways coordinating the alkaline pH response confer resistance to the hevein-type plant antimicrobial peptide Pn-AMP1 in Saccharomyces cerevisiae

Genome-wide screening of Saccharomyces cerevisiae revealed that signaling pathways related to the alkaline pH stress contribute to resistance to plant antimicrobial peptide, Pn-AMP1. Plant antimicrobial peptides (AMPs) are considered to be promising candidates for controlling phytopathogens. Pn-AMP1 is a hevein-type plant AMP that shows potent and broad-spectrum antifungal activity. Genome-wide chemogenomic screening was performed using heterozygous and homozygous diploid deletion pools of Saccharomyces cerevisiae as a chemogenetic model system to identify genes whose deletion conferred enhanced sensitivity to Pn-AMP1. This assay identified 44 deletion strains with fitness defects in the presence of Pn-AMP1. Strong fitness defects were observed in strains with deletions of genes encoding components of several pathways and complex known to participate in the adaptive response to alkaline pH stress, including the cell wall integrity (CWI), calcineurin/Crz1, Rim101, SNF1 pathways and endosomal sorting complex required for transport (ESCRT complex). Gene ontology (GO) enrichment analysis of these genes revealed that the most highly overrepresented GO term was "cellular response to alkaline pH". We found that 32 of the 44 deletion strains tested (72 %) showed significant growth defects compared with their wild type at alkaline pH. Furthermore, 9 deletion strains (20 %) exhibited enhanced sensitivity to Pn-AMP1 at ambient pH compared to acidic pH. Although several hundred plant AMPs have been reported, their modes of action remain largely uncharacterized. This study demonstrates that the signaling pathways that coordinate the adaptive response to alkaline pH also confer resistance to a hevein-type plant AMP in S. cerevisiae. Our findings have broad implications for the design of novel and potent antifungal agents.

Plant Defensins NaD1 and NaD2 Induce Different Stress Response Pathways in Fungi

Nicotiana alata defensins 1 and 2 (NaD1 and NaD2) are plant defensins from the ornamental tobacco that have antifungal activity against a variety of fungal pathogens. Some plant defensins interact with fungal cell wall O-glycosylated proteins. Therefore, we investigated if this was the case for NaD1 and NaD2, by assessing the sensitivity of the three Aspergillus nidulans (An) O-mannosyltransferase (pmt) knockout (KO) mutants (An∆pmtA, An∆pmtB, and An∆pmtC). An∆pmtA was resistant to both defensins, while An∆pmtC was resistant to NaD2 only, suggesting NaD1 and NaD2 are unlikely to have a general interaction with O-linked side chains. Further evidence of this difference in the antifungal mechanism was provided by the dissimilarity of the NaD1 and NaD2 sensitivities of the Fusarium oxysporum f. sp. lycopersici (Fol) signalling knockout mutants from the cell wall integrity (CWI) and high osmolarity glycerol (HOG) mitogen-activated protein kinase (MAPK) pathways. HOG pathway mutants were sensitive to both NaD1 and NaD2, while CWI pathway mutants only displayed sensitivity to NaD2.

Antifungal effect and action mechanism of antimicrobial peptide polybia-CP

The incidence of life-threatening invasive fungal infections increased significantly in recent years. However, the antifungal therapeutic options are very limited. Antimicrobial peptides are a class of potential lead chemical for the development of novel antifungal agents. Antimicrobial peptide polybia-CP was purified from the venom of the social wasp Polybia paulista. In this study, we synthesized polybia-CP and determined its antifungal effects against a series of Candidian species. Our results showed that polybia-CP has potent antifungal activity and fungicidal activity against the tested fungal cells with a proposed membrane-active action mode. In addition, polybia-CP could induce the increase of cellular reactive oxygen species production, which would attribute to its antifungal activity. In conclusion, the present study suggests that polybia-CP has potential as an antifungal agent or may offer a new strategy for antifungal therapeutic option.

The Penicillium digitatum protein O-mannosyltransferase Pmt2 is required for cell wall integrity, conidiogenesis, virulence and sensitivity to the antifungal peptide PAF26

The activity of protein O-mannosyltransferases (Pmts) affects the morphogenesis and virulence of fungal pathogens. Recently, PMT genes have been shown to determine the sensitivity of Saccharomyces cerevisiae to the antifungal peptide PAF26. This study reports the identification and characterization of the three Pdpmt genes in the citrus post-harvest pathogen Penicillium digitatum. The Pdpmt genes are expressed during fungal growth and fruit infection, with the highest induction for Pdpmt2. Pdpmt2 complemented the growth defect of the S. cerevisiae Δpmt2 strain. The Pdpmt2 gene mutation in P. digitatum caused pleiotropic effects, including a reduction in fungal growth and virulence, whereas its constitutive expression had no phenotypic effect. The Pdpmt2 null mutants also showed a distinctive colourless phenotype with a strong reduction in the number of conidia, which was associated with severe alterations in the development of conidiophores. Additional effects of the Pdpmt2 mutation were hyphal morphological alterations, increased sensitivity to cell wall-interfering compounds and a blockage of invasive growth. In contrast, the Pdpmt2 mutation increased tolerance to oxidative stress and to the antifungal activity of PAF26. These data confirm the role of protein O-glycosylation in the PAF26-mediated antifungal mechanism present in distantly related fungal species. Important to future crop protection strategies, this study demonstrates that a mutation rendering fungi more resistant to an antifungal peptide results in severe deleterious effects on fungal growth and virulence.

Multitasking antimicrobial peptides in plant development and host defense against biotic/abiotic stress

Crop losses due to pathogens are a major threat to global food security. Plants employ a multilayer defense against a pathogen including the use of physical barriers (cell wall), induction of hypersensitive defense response (HR), resistance (R) proteins, and synthesis of antimicrobial peptides (AMPs). Unlike a complex R gene-mediated immunity, AMPs directly target diverse microbial pathogens. Many a times, R-mediated immunity breaks down and plant defense is compromised. Although R-gene dependent pathogen resistance has been well studied, comparatively little is known about the interactions of AMPs with host defense and physiology. AMPs are ubiquitous, low molecular weight peptides that display broad spectrum resistance against bacteria, fungi and viruses. In plants, AMPs are mainly classified into cyclotides, defensins, thionins, lipid transfer proteins, snakins, and hevein-like vicilin-like and knottins. Genetic distance lineages suggest their conservation with minimal effect of speciation events during evolution. AMPs provide durable resistance in plants through a combination of membrane lysis and cellular toxicity of the pathogen. Plant hormones - gibberellins, ethylene, jasmonates, and salicylic acid, are among the physiological regulators that regulate the expression of AMPs. Transgenically produced AMP-plants have become a means showing that AMPs are able to mitigate host defense responses while providing durable resistance against pathogens.

Novel mode of action of plant defense peptides - hevein-like antimicrobial peptides from wheat inhibit fungal metalloproteases

The multilayered plant immune system relies on rapid recognition of pathogen-associated molecular patterns followed by activation of defense-related genes, resulting in the reinforcement of plant cell walls and the production of antimicrobial compounds. To suppress plant defense, fungi secrete effectors, including a recently discovered Zn-metalloproteinase from Fusarium verticillioides, named fungalysin Fv-cmp. This proteinase cleaves class IV chitinases, which are plant defense proteins that bind and degrade chitin of fungal cell walls. In this study, we investigated plant responses to such pathogen invasion, and discovered novel inhibitors of fungalysin. We produced several recombinant hevein-like antimicrobial peptides named wheat antimicrobial peptides (WAMPs) containing different amino acids (Ala, Lys, Glu, and Asn) at the nonconserved position 34. An additional Ser at the site of fungalysin proteolysis makes the peptides resistant to the protease. Moreover, an equal molar concentration of WAMP-1b or WAMP-2 to chitinase was sufficient to block the fungalysin activity, keeping the chitinase intact. Thus, WAMPs represent novel protease inhibitors that are active against fungal metalloproteases. According to in vitro antifungal assays WAMPs directly inhibited hyphal elongation, suggesting that fungalysin plays an important role in fungal development. A novel molecular mechanism of dynamic interplay between host defense molecules and fungal virulence factors is suggested.

Activation of stress signalling pathways enhances tolerance of fungi to chemical fungicides and antifungal proteins

Fungal disease is an increasing problem in both agriculture and human health. Treatment of human fungal disease involves the use of chemical fungicides, which generally target the integrity of the fungal plasma membrane or cell wall. Chemical fungicides used for the treatment of plant disease, have more diverse mechanisms of action including inhibition of sterol biosynthesis, microtubule assembly and the mitochondrial respiratory chain. However, these treatments have limitations, including toxicity and the emergence of resistance. This has led to increased interest in the use of antimicrobial peptides for the treatment of fungal disease in both plants and humans. Antimicrobial peptides are a diverse group of molecules with differing mechanisms of action, many of which remain poorly understood. Furthermore, it is becoming increasingly apparent that stress response pathways are involved in the tolerance of fungi to both chemical fungicides and antimicrobial peptides. These signalling pathways such as the cell wall integrity and high-osmolarity glycerol pathway are triggered by stimuli, such as cell wall instability, changes in osmolarity and production of reactive oxygen species. Here we review stress signalling induced by treatment of fungi with chemical fungicides and antifungal peptides. Study of these pathways gives insight into how these molecules exert their antifungal effect and also into the mechanisms used by fungi to tolerate sub-lethal treatment by these molecules. Inactivation of stress response pathways represents a potential method of increasing the efficacy of antifungal molecules.

The use of versatile plant antimicrobial peptides in agribusiness and human health

Plant immune responses involve a wide diversity of physiological reactions that are induced by the recognition of pathogens, such as hypersensitive responses, cell wall modifications, and the synthesis of antimicrobial molecules including antimicrobial peptides (AMPs). These proteinaceous molecules have been widely studied, presenting peculiar characteristics such as conserved domains and a conserved disulfide bond pattern. Currently, many AMP classes with diverse modes of action are known, having been isolated from a large number of organisms. Plant AMPs comprise an interesting source of studies nowadays, and among these there are reports of different classes, including defensins, albumins, cyclotides, snakins and several others. These peptides have been widely used in works that pursue human disease control, including nosocomial infections, as well as for agricultural purposes. In this context, this review will focus on the relevance of the structural-function relations of AMPs derived from plants and their proper use in applications for human health and agribusiness.

Properties and mechanisms of action of naturally occurring antifungal peptides

Antimicrobial peptides are a vital component of the innate immune system of all eukaryotic organisms and many of these peptides have potent antifungal activity. They have potential application in the control of fungal pathogens that are a serious threat to both human health and food security. Development of antifungal peptides as therapeutics requires an understanding of their mechanism of action on fungal cells. To date, most research on antimicrobial peptides has focused on their activity against bacteria. Several antimicrobial peptides specifically target fungal cells and are not active against bacteria. Others with broader specificity often have different mechanisms of action against bacteria and fungi. This review focuses on the mechanism of action of naturally occurring antifungal peptides from a diverse range of sources including plants, mammals, amphibians, insects, crabs, spiders, and fungi. While antimicrobial peptides were originally proposed to act via membrane permeabilization, the mechanism of antifungal activity for these peptides is generally more complex and often involves entry of the peptide into the cell.

FLO11 Gene Is Involved in the Interaction of Flor Strains of Saccharomyces cerevisiae with a Biofilm-Promoting Synthetic Hexapeptide

Saccharomyces cerevisiae "flor" yeasts have the ability to form a buoyant biofilm at the air-liquid interface of wine. The formation of biofilm, also called velum, depends on FLO11 gene length and expression. FLO11 encodes a cell wall mucin-like glycoprotein with a highly O-glycosylated central domain and an N-terminal domain that mediates homotypic adhesion between cells. In the present study, we tested previously known antimicrobial peptides with different mechanisms of antimicrobial action for their effect on the viability and ability to form biofilm of S. cerevisiae flor strains. We found that PAF26, a synthetic tryptophan-rich cationic hexapeptide that belongs to the class of antimicrobial peptides with cell-penetrating properties, but not other antimicrobial peptides, enhanced biofilm formation without affecting cell viability in ethanol-rich medium. The PAF26 biofilm enhancement required a functional FLO11 but was not accompanied by increased FLO11 expression. Moreover, fluorescence microscopy and flow cytometry analyses showed that the PAF26 peptide binds flor yeast cells and that a flo11 gene knockout mutant lost the ability to bind PAF26 but not P113, a different cell-penetrating antifungal peptide, demonstrating that the FLO11 gene is selectively involved in the interaction of PAF26 with cells. Taken together, our data suggest that the cationic and hydrophobic PAF26 hexapeptide interacts with the hydrophobic and negatively charged cell wall, favoring Flo11p-mediated cell-to-cell adhesion and thus increasing biofilm biomass formation. The results are consistent with previous data that point to glycosylated mucin-like proteins at the fungal cell wall as potential interacting partners for antifungal peptides.

Analysis of tyrosine phosphorylation and phosphotyrosine-binding proteins in germinating seeds from Scots pine

Protein tyrosine phosphorylation in angiosperms has been implicated in various physiological processes, including seed development and germination. In conifers, the role of tyrosine phosphorylation and the mechanisms of its regulation are yet to be investigated. In this study, we examined the profile of protein tyrosine phosphorylation in Scots pine seeds at different stages of germination. We detected extensive protein tyrosine phosphorylation in extracts from Scots pine (Pinus sylvestris L.) dormant seeds. In addition, the pattern of tyrosine phosphorylation was found to change significantly during seed germination, especially at earlier stages of post-imbibition which coincides with the initiation of cell division, and during the period of intensive elongation of hypocotyls. To better understand the molecular mechanisms of phosphotyrosine signaling, we employed affinity purification and mass spectrometry for the identification of pTyr-binding proteins from the extracts of Scots pine seedlings. Using this approach, we purified two proteins of 10 and 43 kDa, which interacted specifically with pTyr-Sepharose and were identified by mass spectrometry as P. sylvestris defensin 1 (PsDef1) and aldose 1-epimerase (EC:5.1.3.3), respectively. Additionally, we demonstrated that both endogenous and recombinant PsDef1 specifically interact with pTyr-Sepharose, but not Tyr-beads. As the affinity purification approach did not reveal the presence of proteins with known pTyr binding domains (SH2, PTB and C2), we suggest that plants may have evolved a different mode of pTyr recognition, which yet remains to be uncovered.

[Defense peptides of plant immune system]

Antimicrobial peptides (AMPs) are natural antibiotics produced by all living organisms to combat pathogens. They are important effector molecules of the immune system both in animals and plants. AMPs are diverse in structure and mode of action. Based on homology of amino acid sequences and 3D structures several AMP families have been distinguished. They are defensins, thionins, lipid transfer proteins, hevein- and knottin-like peptides, and cyclotides. AMPs display broad-spectrum antimicrobial activity and thus show promise for the development of disease- resistant crops by genetic engineering and for the production of new-generation drugs. In this paper, the properties of the main AMP families (defensins and hevein-like peptides) and of a new 4-Cys plant AMP family are reviewed.

Antifungal activity of novel synthetic peptides by accumulation of reactive oxygen species (ROS) and disruption of cell wall against Candida albicans

In the present work, we investigated the antifungal activity of two de novo designed, antimicrobial peptides VS2 and VS3, incorporating unnatural amino acid α,β-dehydrophenylalanine (ΔPhe). We observed that the low-hemolytic peptides could irreversibly inhibit the growth of various Candida species and multidrug resistance strains at MIC(80) values ranging from 15.62 μM to 250 μM. Synergy experiments showed that MIC(80) of the peptides was drastically reduced in combination with an antifungal drug fluconazole. The dye PI uptake assay was used to demonstrate peptide induced cell membrane permeabilization. Intracellular localization of the FITC-labeled peptides in Candida albicans was studied by confocal microscopy and FACS. Killing kinetics, PI uptake assay, and the intracellular presence of FITC-peptides suggested that growth inhibition is not solely a consequence of increased membrane permeabilization. We showed that entry of the peptide in Candida cells resulted in accumulation of reactive oxygen species (ROS) leading to cell necrosis. Morphological alteration in Candida cells caused by the peptides was visualized by electron microscopy. We propose that de novo designed VS2 and VS3 peptides have multiple detrimental effects on target fungi, which ultimately result in cell wall disruption and killing. Therefore, these peptides represent a good template for further design and development as antifungal agents.

Multifunctional cationic host defence peptides and their clinical applications

With the rapid rise in the emergence of bacterial strains resistant to multiple classes of antimicrobial agents, there is an urgent need to develop novel antimicrobial therapies to combat these pathogens. Cationic host defence peptides (HDPs) and synthetic derivatives termed innate defence regulators (IDRs) represent a promising alternative approach in the treatment of microbial-related diseases. Cationic HDPs (also termed antimicrobial peptides) have emerged from their origins as nature's antibiotics and are widely distributed in organisms from insects to plants to mammals and non-mammalian vertebrates. Although their original and primary function was proposed to be direct antimicrobial activity against bacteria, fungi, parasites and/or viruses, cationic HDPs are becoming increasingly recognized as multifunctional mediators, with both antimicrobial activity and diverse immunomodulatory properties. Here we provide an overview of the antimicrobial and immunomodulatory activities of cationic HDPs, and discuss their potential application as beneficial therapeutics in overcoming infectious diseases.

A genomic approach highlights common and diverse effects and determinants of susceptibility on the yeast Saccharomyces cerevisiae exposed to distinct antimicrobial peptides

Background

The mechanism of action of antimicrobial peptides (AMP) was initially correlated with peptide membrane permeation properties. However, recent evidences indicate that action of a number of AMP is more complex and involves specific interactions at cell envelopes or with intracellular targets. In this study, a genomic approach was undertaken on the model yeast Saccharomyces cerevisiae to characterize the antifungal effect of two unrelated AMP.

Results

Two differentiated peptides were used: the synthetic cell-penetrating PAF26 and the natural cytolytic melittin. Transcriptomic analyses demonstrated distinctive gene expression changes for each peptide. Quantitative RT-PCR confirmed differential expression of selected genes. Gene Ontology (GO) annotation of differential gene lists showed that the unique significant terms shared by treatment with both peptides were related to the cell wall (CW). Assays with mutants lacking CW-related genes including those of MAPK signaling pathways revealed genes having influence on sensitivity to peptides. Fluorescence microscopy and flow cytometry demonstrated PAF26 interaction with cells and internalization that correlated with cell killing in sensitive CW-defective mutants such as Δecm33 or Δssd1. GO annotation also showed differential responses between peptides, which included ribosomal biogenesis, ARG genes from the metabolism of amino groups (specifically induced by PAF26), or the reaction to unfolded protein stress. Susceptibility of deletion mutants confirmed the involvement of these processes. Specifically, mutants lacking ARG genes from the metabolism of arginine pathway were markedly more resistant to PAF26 and had a functional CW. In the deletant in the arginosuccinate synthetase (ARG1) gene, PAF26 interaction occurred normally, thus uncoupling peptide interaction from cell killing. The previously described involvement of the glycosphingolipid gene IPT1 was extended to the peptides studied here.

Conclusions

Reinforcement of CW is a general response common after exposure to distinct AMP, and likely contributes to shield cells from peptide interaction. However, a weakened CW is not necessarily indicative of a higher sensitivity to AMP. Additional processes modulate susceptibility to specific peptides, exemplified in the involvement of the metabolism of amino groups in the case of PAF26. The relevance of the response to unfolded protein stress or the sphingolipid biosynthesis, previously reported for other unrelated AMP, was also independently confirmed.

An integrated analysis of the effects of Esculentin 1-21 on Saccharomyces cerevisiae

The antimicrobial peptide esculentin 1-21 (Esc 1-21) is a shorter synthetic version of the 46-residue peptide occurring in the Rana esculenta skin secretion. Here we propose an integrated proteomic and transcriptomic approach to interpret the biological effects of this peptide on Saccharomyces cerevisiae. We further investigated the response to this peptide by correlating the results of the transcriptome and proteome analysis with phenotypic effects. The results show that S. cerevisiae adapts to Esc 1-21 using the High Osmolarity Glycerol (HOG) pathway involved in osmotic tolerance and cell wall maintenance. Comparative proteomics reveals that Esc 1-21 causes downregulation of enzymes of the lower glycolytic pathway and in genes involved in spindle body formation and remodelling of cell-wall synthesis. Moreover the peptide induces downexpression of protein actin within 45 min and cells pre-treated with peptide show less sensitivity to osmotic stress and increased sensitivity to heat shock stress. The results obtained with the two different methodologies are in agreement at the cellular process levels. A combined approach may help elucidate the main aspects related to the effects of this peptide on the eukaryotic cell. The employment of different technologies may reveal the potential and limitations of each adapted approach in a prospective application for drug screening.

Peptide antimicrobial agents

Antimicrobial host defense peptides are produced by all complex organisms as well as some microbes and have diverse and complex antimicrobial activities. Collectively these peptides demonstrate a broad range of antiviral and antibacterial activities and modes of action, and it is important to distinguish between direct microbicidal and indirect activities against such pathogens. The structural requirements of peptides for antiviral and antibacterial activities are evaluated in light of the diverse set of primary and secondary structures described for host defense peptides. Peptides with antifungal and antiparasitic activities are discussed in less detail, although the broad-spectrum activities of such peptides indicate that they are important host defense molecules. Knowledge regarding the relationship between peptide structure and function as well as their mechanism of action is being applied in the design of antimicrobial peptide variants as potential novel therapeutic agents.

Plant-derived antifungal proteins and peptides

Plants produce potent constitutive and induced antifungal compounds to complement the structural barriers to microbial infection. Approximately 250 000 – 500 000 plant species exist, but only a few of these have been investigated for antimicrobial activity. Nevertheless, a wide spectrum of compound classes have been purified and found to have antifungal properties. The commercial potential of effective plant-produced antifungal compounds remains largely unexplored. This review article presents examples of these compounds and discusses their properties.Key words: antifungal, peptides, phytopathogenic, plants, proteins.