Deciphering antifungal and antibiofilm mechanisms of isobavachalcone against Cryptococcus neoformans through RNA-seq and functional analyses

Cryptococcus neoformans has been designated as critical fungal pathogens by the World Health Organization, mainly due to limited treatment options and the prevalence of antifungal resistance. Consequently, the utilization of novel antifungal agents is crucial for the effective treatment of C. neoformans infections. This study exposed that the minimum inhibitory concentration (MIC) of isobavachalcone (IBC) against C. neoformans H99 was 8 µg/mL, and IBC dispersed 48-h mature biofilms by affecting cell viability at 16 µg/mL. The antifungal efficacy of IBC was further validated through microscopic observations using specific dyes and in vitro assays, which confirmed the disruption of cell wall/membrane integrity. RNA-Seq analysis was employed to decipher the effect of IBC on the C. neoformans H99 transcriptomic profiles. Real-time quantitative reverse transcription PCR (RT-qPCR) analysis was performed to validate the transcriptomic data and identify the differentially expressed genes. The results showed that IBC exhibited various mechanisms to impede the growth, biofilm formation, and virulence of C. neoformans H99 by modulating multiple dysregulated pathways related to cell wall/membrane, drug resistance, apoptosis, and mitochondrial homeostasis. The transcriptomic findings were corroborated by the antioxidant analyses, antifungal drug sensitivity, molecular docking, capsule, and melanin assays. In vivo antifungal activity analysis demonstrated that IBC extended the lifespan of C. neoformans-infected Caenorhabditis elegans. Overall, the current study unveiled that IBC targeted multiple pathways simultaneously to inhibit growth significantly, biofilm formation, and virulence, as well as to disperse mature biofilms of C. neoformans H99 and induce cell death.

Distinct membrane perturbation effects of Catestatin and its CST-364 S variant: Insights from molecular simulations and anisotropy measurements

Catestatin (CST), a versatile 21 amino acid long cationic peptide, is stored in chromaffin granules and exocytosed upon fusion with the plasma membrane. CST, produced by chromaffin cells and neutrophils, is derived from the processing of chromogranin A and induced in the skin after injury. It involves catecholamine inhibition, blood pressure control, inflammation, and innate immunity. It is thought that calcium influx is triggered by CST permeating within neutrophils. It is unknown whether CST can disturb the immediate environment enough to penetrate the cell membrane passively. We used molecular dynamics simulations to examine the behaviour of human CST in its wild-type state (CST WT) and one of its naturally occurring variants, CST-364 S, which has a high allelic frequency in the human population. Both peptides were incorporated into the model eukaryotic cell membrane known as the POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine) lipid bilayer. The molecular modelling and simulations results show that CST WT and CST-364 S have different propensities for membrane disruption. It was shown that CST-364 S has higher membrane permeability than CST WT. In addition, we have used fluorescence anisotropy and leakage assay to study the interaction of peptides with PC membranes. Both peptides interacted with POPC and DOPC membranes, while CST-364 S penetrated the membrane more deeply via disorganizing the membrane interface, which supports our previous findings. According to this study, there is a good possibility that the peptides will passively permeate the cell membrane, distort, and pass through it.

Recent Advances in Multifunctional Antimicrobial Peptides as Immunomodulatory and Anticancer Therapy: Chromogranin A-Derived Peptides and Dermaseptins as Endogenous versus Exogenous Actors

Antimicrobial peptides (AMPs) are produced by all living organisms exhibiting antimicrobial activities and representing the first line of innate defense against pathogens. In this context, AMPs are suggested as an alternative to classical antibiotics. However, several researchers reported their involvement in different processes defining them as Multifunctional AMPs (MF-AMPs). Interestingly, these agents act as the endogenous responses of the human organism against several dangerous stimuli. Still, they are identified in other organisms and evaluated for their anticancer therapy. Chromogranin A (CgA) is a glyco-phosphoprotein discovered for the first time in the adrenal medulla but also produced in several cells. CgA can generate different derived AMPs influencing numerous physiological processes. Dermaseptins (DRSs) are a family of α-helical-shaped polycationic peptides isolated from the skin secretions of several leaf frogs from the Phyllomedusidae family. Several DRSs were identified as AMPs and, until now, more than 65 DRSs have been classified. Recently, these exogenous molecules were characterized for their anticancer activity. In this review, we summarize the role of these two classes of MF-AMPs as an example of endogenous molecules for CgA-derived peptides, able to modulate inflammation but also as exogenous molecules for DRSs, exerting anticancer activities.

Antimicrobial Peptides with Anti-Candida Activity

Mycoses are accountable for millions of infections yearly worldwide. Invasive candidiasis is the most usual, presenting a high morbidity and mortality. Candida albicans remains the prevalent etiologic agent, but the incidence of other species such as Candida parapsilosis, Candida glabrata and Candida auris keeps increasing. These pathogens frequently show a reduced susceptibility to commonly used antifungal drugs, including polyenes, triazoles and echinocandins, and the incidence of emerging multi-drug-resistant strains of these species continues to increase. Therefore, the need to search for new molecules that target these pathogenic species in a different manner is now more urgent than ever. Nature is an almost endless source of interesting new molecules that could meet this need. Among these molecules, antimicrobial peptides, present in different sources in nature, possess some advantages over conventional antifungal agents, even with their own drawbacks, and are considered as a promising pharmacological option against a wide range of microbial infections. In this review, we describe 20 antimicrobial peptides from different origins that possess an activity against Candida.

Quantitative biophysical analysis defines key components modulating recruitment of the GTPase KRAS to the plasma membrane

The gene encoding the GTPase KRAS is frequently mutated in pancreatic, lung, and colorectal cancers. The KRAS fraction in the plasma membrane (PM) correlates with activation of the mitogen-activated protein kinase (MAPK) pathway and subsequent cellular proliferation. Understanding KRAS's interaction with the PM is challenging given the complexity of the cellular environment. To gain insight into key components necessary for KRAS signal transduction at the PM, we used synthetic membranes such as liposomes and giant unilamellar vesicles. Using surface plasmon resonance (SPR) spectroscopy, we demonstrated that KRAS and Raf-1 proto-oncogene Ser/Thr kinase (RAF1) domains interact with these membranes primarily through electrostatic interactions with negatively charged lipids reinforced by additional interactions involving phosphatidyl ethanolamine and cholesterol. We found that the RAF1 region spanning RBD through CRD (RBDCRD) interacts with the membrane significantly more strongly than the isolated RBD or CRD domains and synergizes KRAS partitioning to the membrane. We also found that calmodulin and phosphodiesterase 6 delta (PDE6δ), but not galectin3 previously proposed to directly interact with KRAS, passively sequester KRAS and prevent it from partitioning into the PM. RAF1 RBDCRD interacted with membranes preferentially at nonraft lipid domains. Moreover, a C-terminal O-methylation was crucial for KRAS membrane localization. These results contribute to a better understanding of how the KRAS-membrane interaction is tuned by multiple factors whose identification could inform drug discovery efforts to disrupt this critical interaction in diseases such as cancer.

Highly potent antimicrobial peptide derivatives of bovine cateslytin

The antimicrobial activity of bovine cateslytin was optimized in a series of sequential modifications leading to synlytin, a highly potent non-haemolytic antimicrobial peptide.

The interaction of aurein 2.5 with fungal membranes

Aurein 2.5 (GLFDIVKKVVGAFGSL-NH2) is an antimicrobial peptide, which was seen to have activity against Stachybotris chartarum, Penicillium roseopurpureum and Aspergillus flavus with minimum fungicidal concentrations in the range 250-500 μM. S. chartarum showed enhanced susceptibility to lysis as compared to P. roseopurpureum and A. flavus, (44, 26 and 28 % respectively). Monolayers formed from lipid membrane extracts derived from S. chartarum, P. roseopurpureum and A. flavus showed maximal surface pressure changes of 13.5, 10.3 and 10.2 mN m(-1) respectively. However, aurein 2.5 adopted similar levels of α-helical structure (circa 45 %) in the presence of vesicles formed from membrane lipid extracts derived from all three fungi. These data imply that differential activity is not due to targeting and membrane association but linked to the ability of the bound peptide to lyse the cells. At sterol levels mimetic of eukaryotic systems, high levels of α-helical structure (circa 50 %) were also observed and hence similar binding. However, enhanced sterol levels (>0.6) led to a reduction in monolayer membrane interaction, suggesting that the sterols influence efficacy. Consistent with this suggestion, thermodynamic analysis showed that the peptide was able to destabilise model fungal monolayers, as indicated by negative values of ∆Gmix.

Biologically active binaphthol-scaffolded imidazolium salts

This work describes the antimicrobial activity and selectivity for Gram-positive bacteria of imidazolium-functionalized binols, as a result of their insertion into the lipid membrane and alteration of its permeability.

Host defense peptides: an alternative as antiinfective and immunomodulatory therapeutics

Host defense peptides are conserved components of innate immune response present among all classes of life. These peptides are potent, broad spectrum antimicrobial agents with potential as novel therapeutic compounds. Also, the ability of host defense peptides to modulate immunity is an emerging therapeutic concept since its selective modulation is a novel antiinfective strategy. Their mechanisms of action and the fundamental differences between pathogens and host cells surfaces mostly lead to a not widely extended microbial resistance and to a lower toxicity toward host cells. Biological libraries and rational design are novel tools for developing such molecules with promising applications as therapeutic drugs.

Lipids of plant membrane rafts

Lipids tend to organize in mono or bilayer phases in a hydrophilic environment. While they have long been thought to be incapable of coherent lateral segregation, it is now clear that spontaneous assembly of these compounds can confer microdomain organization beyond spontaneous fluidity. Membrane raft microdomains have the ability to influence spatiotemporal organization of protein complexes, thereby allowing regulation of cellular processes. In this review, we aim at summarizing briefly: (i) the history of raft discovery in animals and plants, (ii) the main findings about structural and signalling plant lipids involved in raft segregation, (iii) imaging of plant membrane domains, and their biochemical purification through detergent-insoluble membranes, as well as the existing debate on the topic. We also discuss the potential involvement of rafts in the regulation of plant physiological processes, and further discuss the prospects of future research into plant membrane rafts.

Effect of cholesterol on the membrane interaction of Modelin-5 isoforms

Modelin-5 isoforms were used to gain an insight into the effects of amidation on antimicrobial selectivity. When tested against Escherichia coli, amidation increased toxicity 10-fold (MIC = 31.25 μM) while showing limited increased hemolytic activity (2% lysis). Our results show that both the amidated and non-amidated peptides had a disordered structure in aqueous solution (<18% helical) and folded to form helices at the membrane interface (for example, >43% in the presence of DMPC). The stabilization of the helical structure by amidation has previously been shown to play a key role in increasing antibacterial efficacy. The presence of cholesterol in the membrane increases the packing density (C(s)(-1) values 25-33 mN m(-1)) and so prevents the peptide from forming stable association with the membrane, which is evidenced by the higher binding coefficient (K(d)) in the presence of cholesterol: 57.70 μM for Modelin-5-COOH and 35.64 μM for Modelin-5-CONH(2) compared to the presence of E. coli lipid extract (10 μM), which would prevent local concentration of the peptide at the bilayer interface as seen by reduction in monolayer interaction. This in turn would be predicted to inhibit activity.

The antimicrobial peptides derived from chromogranin/secretogranin family, new actors of innate immunity

Chromogranins/secretogranins are members of the granin family present in secretory vesicles of nervous, endocrine and immune cells. In chromaffin cells, activation of nicotinic cholinergic receptors induces the release, with catecholamines, of bioactive peptides resulting from a natural processing. During the past decade, our laboratory has characterized new antimicrobial chromogranin-derived peptides in the secretions of stimulated bovine chromaffin cells. They act at the micromolar range against bacteria, fungi, yeasts, and are non-toxic for the mammalian cells. They are recovered in several biological fluids involved in defence mechanisms (human serum, neutrophil secretions and saliva). These new antimicrobial peptides demonstrate the major role of the adrenal medulla in innate immunity. In this review we focus on the antimicrobial peptides derived from human and bovine chromogranin A (CGA), chromogranin B (CGB) and secretogranin II (SGII) emphasizing their direct action against pathogens and their effects on immune cells.