Characterization of membrane-interaction mechanisms of proteins using vacuum-ultraviolet circular dichroism spectroscopy.

Protein-membrane interactions play an important role in various biological phenomena, such as material transport, demyelinating diseases, and antimicrobial activity. We combined vacuum-ultraviolet circular dichroism (VUVCD) spectroscopy with theoretical (e.g., molecular dynamics and neural networks) and polarization experimental (e.g., linear dichroism and fluorescence anisotropy) methods to characterize the membrane interaction mechanisms of three soluble proteins (or peptides). α1 -Acid glycoprotein has the drug-binding ability, but the combination of VUVCD and neural-network method revealed that the membrane interaction causes the extension of helix in the N-terminal region, which reduces the binding ability. Myelin basic protein (MBP) is an essential component of the myelin sheath with a multi-layered structure. Molecular dynamics simulations using a VUVCD-guided system showed that MBP forms two amphiphilic and three non-amphiphilic helices as membrane interaction sites. These multivalent interactions may allow MBP to interact with two opposing membrane leaflets, contributing to the formation of a multi-layered myelin structure. The antimicrobial peptide magainin 2 interacts with the bacterial membrane, causing damage to its structure. VUVCD analysis revealed that the M2 peptides assemble in the membrane and turn into oligomers with a ß-strand structure. Linear dichroism and fluorescence anisotropy suggested that the oligomers are inserted into the hydrophobic core of the membrane, disrupting the bacterial membrane. Overall, our findings demonstrate that VUVCD and its combination with theoretical and polarization experimental methods pave the way for unraveling the molecular mechanisms of biological phenomena related to protein-membrane interactions.

Differentiation of PANC-1 ductal cells to ß-like cells via cellular GABA modulation by Magainin and CPF-7 peptides.

Some of the antimicrobial peptides induce insulin release and improve glucose tolerance while their effects on pancreatic cell differentiation have remained unresolved. In this report, we evaluated the effects of two of these peptides, Magainin-II and CPF-7, and also GABA, on PANC-1 ductal cells' differentiation. Based on immunofluorescence and qRT-PCR analyses the expression levels of some of the Epithelial to Mesenchymal transition (EMT)-related factors such as Snai1 and Ngn3, as two biomarkers of alpha and beta cells, were increased. Our findings also revealed a drastic increase in Arx, Pax4, Dnmt-1 and Glucagon expressions associated with dedifferentiation of PANC-1 cells into pancreatic endocrine progenitor cells. Futhermore, Magainin-II and CPF-7 exerted their roles partly via influencing the GABA cellular content. These data would undoubtedly provide a suitable ground for further investigation to guide these cells toward transplantable insulin producing beta cells.

A magainin-2 like bacteriocin BpSl14 with anticancer action from fish gut Bacillus safensis SDG14.

Bacteriocins are gaining utmost importance in antimicrobial and chemotherapy due to their diverse structure and activity. This study centres on magainin-2 like bacteriocin with anticancer action, produced by Bacillus safensis strain SDG14 isolated from gut of marine fish Sardinella longiceps. The purified bacteriocin designated as BpSl14 was thermostable and pH tolerant. The molecular weight of BpS114 was estimated to be 6061.2 Da using MALDI-ToF MS. The partial primary sequence was elucidated by peptide mass fingerprinting using MALDI MS/MS. The tertiary structure of the partial sequence was similar to that of two magainin-2 α-helices joined together by extended indolicidin. The BpSl14 protein inhibited the cells of lung carcinoma, one of the deadliest cancers. Docking studies conducted with DR5 and TGF-ß, two of the most prominent apoptotic receptors in adenocarcinoma, also proved the anti-apoptotic action of BpSl14.

Development of Antimicrobial Stapled Peptides Based on Magainin 2 Sequence.

Magainin 2 (Mag2), which was isolated from the skin of the African clawed frog, is a representative antimicrobial peptide (AMP) that exerts antimicrobial activity via microbial membrane disruption. It has been reported that the helicity and amphipathicity of Mag2 play important roles in its antimicrobial activity. We investigated and recently reported that 17 amino acid residues of Mag2 are required for its antimicrobial activity, and accordingly developed antimicrobial foldamers containing α,α-disubstituted amino acid residues. In this study, we further designed and synthesized a set of Mag2 derivatives bearing the hydrocarbon stapling side chain for helix stabilization. The preferred secondary structures, antimicrobial activities, and cell-membrane disruption activities of the synthesized peptides were evaluated. Our analyses revealed that hydrocarbon stapling strongly stabilized the helical structure of the peptides and enhanced their antimicrobial activity. Moreover, peptide 2 stapling between the first and fifth position from the N-terminus showed higher antimicrobial activity than that of Mag2 against both gram-positive and gram-negative bacteria without exerting significant hemolytic activity. To investigate the modes of action of tested peptides 2 and 8 in antimicrobial and hemolytic activity, electrophysiological measurements were performed.

Lipid topology and electrostatic interactions underpin lytic activity of linear cationic antimicrobial peptides in membranes.

Linear cationic antimicrobial peptides are a diverse class of molecules that interact with a wide range of cell membranes. Many of these peptides disrupt cell integrity by forming membrane-spanning pores that ultimately lead to their death. Despite these peptides high potency and ability to evade acquired bacterial drug resistance, there is a lack of knowledge on their selectivity and activity mechanisms. Such an understanding would provide an informative framework for rational design and could lead to potential antimicrobial therapeutic targets. In this paper, we use a high-throughput microfluidic platform as a quantitative screen to assess peptide activity and selectivity by precisely controlling exposure to vesicles with lipid compositions that mimic both bacterial and mammalian cell membranes. We explore the complexity of the lipid-peptide interactions governing membrane-disruptive behaviors and establish a link between peptide pore formation and both lipid-peptide charge and topological interactions. We propose a topological model for linear antimicrobial peptide activity based on the increase in membrane strain caused by the continuous adsorption of peptides to the target vesicle coupled with the effects of both lipid-peptide charge and topographical interactions. We also show the validity of the proposed model by investigating the activity of two prototypical linear cationic peptides: magainin 2 amide (which is selective for bacterial cells) and melittin (which targets both mammalian and bacterial cells indiscriminately). Finally, we propose the existence of a negative feedback mechanism that governs the pore formation process and controls the membrane's apparent permeability.

Review: Examining the Natural Role of Amphibian Antimicrobial Peptide Magainin.

Host defense peptides (HDPs) are a group of antimicrobial peptides (AMPs) that are crucial components of the innate immune system of many different organisms. These small peptides actively kill microbes and prevent infection. Despite the presence of AMPs in the amphibian immune system, populations of these organisms are in decline globally. Magainin is an AMP derived from the African clawed frog (Xenopus laevis) and has displayed potent antimicrobial effects against a wide variety of microbes. Included in this group of microbes are known pathogens of the African clawed frog and other amphibian species. Arguably, the most deleterious amphibious pathogen is Batrachochytrium dendrobatidis, a chytrid fungus. Investigating the mechanism of action of magainin can help understand how to effectively fight off infection. By understanding amphibian AMPs' role in the frog, a potential conservation strategy can be developed for other species of amphibians that are susceptible to infections, such as the North American green frog (Rana clamitans). Considering that population declines of these organisms are occurring globally, this effort is crucial to protect not only these organisms but the ecosystems they inhabit as well.

The Mechanisms of Action of Cationic Antimicrobial Peptides Refined by Novel Concepts from Biophysical Investigations.

Even 30 years after the discovery of magainins, biophysical and structural investigations on how these peptides interact with membranes can still bear surprises and add new interesting detail to how these peptides exert their antimicrobial action. Early on, using oriented solid-state NMR spectroscopy, it was found that the amphipathic helices formed by magainins are active when being oriented parallel to the membrane surface. More recent investigations indicate that this in-planar alignment is also found when PGLa and magainin in combination exert synergistic pore-forming activities, where studies on the mechanism of synergistic interaction are ongoing. In a related manner, the investigation of dimeric antimicrobial peptide sequences has become an interesting topic of research which bears promise to refine our views how antimicrobial action occurs. The molecular shape concept has been introduced to explain the effects of lipids and peptides on membrane morphology, locally and globally, and in particular of cationic amphipathic helices that partition into the membrane interface. This concept has been extended in this review to include more recent ideas on soft membranes that can adapt to external stimuli including membrane-disruptive molecules. In this manner, the lipids can change their shape in the presence of low peptide concentrations, thereby maintaining the bilayer properties. At higher peptide concentrations, phase transitions occur which lead to the formation of pores and membrane lytic processes. In the context of the molecular shape concept, the properties of lipopeptides, including surfactins, are shortly presented, and comparisons with the hydrophobic alamethicin sequence are made.

Design, recombinant expression, and antibacterial activity of a novel hybrid magainin-thanatin antimicrobial peptide.

Antimicrobial peptides are small molecule polypeptides with biological activity, which can avoid the drug resistance. Magainin and thanatin are antimicrobial peptides with a broad spectrum of inhibitory microbes, and the core sequence of magainin is linked to a core sequence of thanatin. Here, the hybrid magainin-thanatin (MT) antimicrobial peptide was designed through bioinformatics analysis. The recombinant MT antimicrobial peptide was successfully expressed and purified in Escherichia coli BL21 (DE3). The molecular weight of the hybrid MT antimicrobial peptide was about 3.35 kDa. Moreover, the target protein indeed has an inhibitory effect on Staphylococcus aureus, E. coli DH5α, and Bacillus subtilis, with the minimum inhibitory concentrations 16.5, 20, and 9 µM, respectively. The rational designed hybrid MT antimicrobial peptide will hopefully provide large-scale fermentable antimicrobial peptides in the industrial production in the future.

Augmentation of endogenous GABA pool size induced by Magainin II peptide.

BACKGROUND: Gamma aminobutyric acid (GABA), an inhibitory neurotransmitter, is produced via decarboxylation of l-glutamate through the glutamic acid decarboxylase (GAD) enzyme. The synchronic action of GABA-transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSADH) enzymes convert the GABA metabolite into succinate. Given this background, our research was aimed at probing the effect of Magainin II, on the activity of GABA shunt metabolizing enzymes. METHODS: Male NIH mice were administered peripherally by Magainin II (50 µg/kg body weight) and saline solution (%0.9 (w/v)) as the control vehicle. At different time intervals, the mice were sacrificed to evaluate the effect of Magainin II injection on the GABA shunt pathway. The activity of hypothalamic GAD, GABA-T and SSADH enzymes were determined using relevant enzyme assays. RESULTS: Magainin II effectively enhanced the activity of GAD, by %90, 24 h after injection, while quenching the activities of GABA-T and SSADH by %43 and %71, respectively. In vitro models also revealed the direct but reversible interaction between the peptide and each of the individual enzymes of GABA shunt pathway. CONCLUSION: This study confirms the probable role of Magainin II in increasing the GABA content of the mouse hypothalamus. This property might candidate the peptide as a novel agent for improving the symptoms of many GABA dependent psychiatric disorders.

Comparative transcriptome analyses of magainin I-susceptible and -resistant Escherichia coli strains.

Antimicrobial peptides (AMPs) have attracted considerable attention because of their multiple and complex mechanisms of action toward resistant bacteria. However, reports have increasingly highlighted how bacteria can escape AMP administration. Here, the molecular mechanisms involved in Escherichia coli resistance to magainin I were investigated through comparative transcriptomics. Sub-inhibitory concentrations of magainin I were used to generate four experimental groups, including magainin I-susceptible E. coli, in the absence (C) and presence of magainin I (CM); and magainin I-resistant E. coli in the absence (R) and presence of magainin I (RM). The total RNA from each sample was extracted; cDNA libraries were constructed and further submitted for Illumina MiSeq sequencing. After RNA-seq data pre-processing and functional annotation, a total of 103 differentially expressed genes (DEGs) were identified, mainly related to bacterial metabolism. Moreover, down-regulation of cell motility and chaperone-related genes was observed in CM and RM, whereas cell communication, acid tolerance and multidrug efflux pump genes (ABC transporter, major facilitator and resistance-nodulation cell division superfamilies) were up-regulated in these same groups. DEGs from the C and R groups are related to basal levels of expression of homeostasis-related genes compared to CM and RM, suggesting that the presence of magainin I is required to change the transcriptomics panel in both C and R E. coli strains. These findings show the complexity of E. coli resistance to magainin I through the rearrangement of several metabolic pathways involved in bacterial physiology and drug response, also providing information on the development of novel antimicrobial strategies targeting resistance-related transcripts and proteins herein described.

Magainin-AM2 improves glucose homeostasis and beta cell function in high-fat fed mice.

BACKGROUND: Magainin-AM2, a previously described amphibian host-defense peptide, stimulates insulin- and glucagon-like peptide-1-release in vitro. This study investigated anti-diabetic effects of the peptide in mice with diet-induced obesity and glucose intolerance. METHODS: Male National Institute of Health Swiss mice were maintained on a high-fat diet for 12-weeks prior to the daily treatment with magainin-AM2. Various indices of glucose tolerance were monitored together with insulin secretory responsiveness of islets at conclusion of study. RESULTS: Following twice daily treatment with magainin-AM2 for 15 days, no significant difference in body weight and food intake was observed compared with saline-treated high fat control animals. However, non-fasting blood glucose was significantly (P<0.05) decreased while plasma insulin concentrations were significantly (P<0.05) increased. Oral and intraperitoneal glucose tolerance and insulin secretion following glucose administration via both routes were significantly (P<0.05) enhanced. The peptide significantly (P<0.001) improved insulin sensitivity as well as the beta cell responses of islets isolated from treated mice to a range of insulin secretagogues. Oxygen consumption, CO2production, respiratory exchange ratio and energy expenditure were not significantly altered by sub-chronic administration of magainin-AM2 but a significant (P<0.05) reduction in fat deposition was observed. CONCLUSION: These results indicate that magainin-AM2 improves glucose tolerance, insulin sensitivity and islet beta cells secretory responsiveness in mice with obesity-diabetes. GENERAL SIGNIFICANCE: The activity of magainin-AM2 suggests the possibility of exploiting this peptide for treatment of type 2 diabetes.

Studies of the mechanism of an antibacterial peptide (cecropinA-magainin) on methicillin-resistant Staphylococcus aureus membranes.

As bacterial resistance becomes increasingly common, a new hybrid peptide, cecropinA-magainin (KWALSKEGPGKFLGKKKKF), has been developed that can kill a broad spectrum of bacteria without damaging human cells. The mechanism of antibacterial toxicity for the hybrid peptides is unknown. Herein, we investigate the localization of the hybrid peptide in methicillin-resistant Staphylococcus aureus (MRSA). The minimum inhibitory concentration was 64 µg/mL. The hybrid peptides could enhance the hydrophobicity of MRSA. Dye leakage experiments showed that the hybrid peptides caused dye leakage from liposomes. The hybrid peptides influenced the permeability of the outer membrane and plasma membrane of MRSA. After cecropinA-magainin treatment of MRSA, the membrane ultrastructure was damaged and the concentration of K+ increased. Ultimately, the peptide destroyed the integrity of the bacterial cell membrane, allowing the dye propidium iodide to enter the cytoplasm. Therefore, the hybrid antibacterial peptide can kill MRSA.

Influence of hydrophobic residues on the activity of the antimicrobial peptide magainin 2 and its synergy with PGLa.

Magainin 2 (MAG2) and PGLa are two related antimicrobial peptides found in the skin of the African frog Xenopus laevis with a pronounced synergistic activity, which act by permeabilizing bacterial membranes. To probe the influence of hydrophobic peptide-lipid and peptide-peptide interactions on the antimicrobial activity and on synergy, the sequence of MAG2 was modified by replacing single amino acids either with a small alanine or with the stiff and bulky hydrophobic 3-(trifluoromethyl)-L-bicyclopent-[1.1.1]-1-ylglycine side chain. The minimum inhibitory concentration of 14 MAG2 analogs was strongly influenced by these single substitutions: the antimicrobial activity was consistently improved when the hydrophobicity was increased on the hydrophobic face of the amphiphilic helix, while the activity decreased when the hydrophobicity was reduced. The synergy with PGLa, on the other hand, was rather insensitive to mutations of hydrophobic residues. It thus seems that the antimicrobial effect of MAG2 on its own depends strongly on the hydrophobicity of the peptide, while the synergy with PGLa does not depend on the overall hydrophobicity of MAG2.

The SMART model: Soft Membranes Adapt and Respond, also Transiently, in the presence of antimicrobial peptides.

Biophysical and structural studies of peptide-lipid interactions, peptide topology and dynamics have changed our view on how antimicrobial peptides insert and interact with membranes. Clearly, both the peptides and the lipids are highly dynamic, change and mutually adapt their conformation, membrane penetration and detailed morphology on a local and a global level. As a consequence, the peptides and lipids can form a wide variety of supramolecular assemblies in which the more hydrophobic sequences preferentially, but not exclusively, adopt transmembrane alignments and have the potential to form oligomeric structures similar to those suggested by the transmembrane helical bundle model. In contrast, charged amphipathic sequences tend to stay intercalated at the membrane interface where they cause pronounced disruptions of the phospholipid fatty acyl packing. At increasing local or global concentrations, the peptides result in transient membrane openings, rupture and ultimately lysis. Depending on peptide-to-lipid ratio, lipid composition and environmental factors (temperature, buffer composition, ionic strength, etc.), the same peptide sequence can result in a variety of those responses. Therefore, the SMART model has been introduced to cover the full range of possibilities. With such a view in mind, novel antimicrobial compounds have been designed from amphipathic polymers, peptide mimetics, combinations of ultra-short polypeptides with hydrophobic anchors or small designer molecules.

On the design of supramolecular assemblies made of peptides and lipid bilayers.

Peptides confer interesting properties to materials, supramolecular assemblies and to lipid membranes and are used in analytical devices or within delivery vehicles. Their relative ease of production combined with a high degree of versatility make them attractive candidates to design new such products. Here, we review and demonstrate how CD- and solid-state NMR spectroscopic approaches can be used to follow the reconstitution of peptides into membranes and to describe some of their fundamental characteristics. Whereas CD spectroscopy is used to monitor secondary structure in different solvent systems and thereby aggregation properties of the highly hydrophobic domain of p24, a protein involved in vesicle trafficking, solid-state NMR spectroscopy was used to deduce structural information and the membrane topology of a variety of peptide sequences found in nature or designed. (15)N chemical shift solid-state NMR spectroscopy indicates that the hydrophobic domain of p24 as well as a designed sequence of 19 hydrophobic amino acid residues adopt transmembrane alignments in phosphatidylcholine membranes. In contrast, the amphipathic antimicrobial peptide magainin 2 and the designed sequence LK15 align parallel to the bilayer surface. Additional angular information is obtained from deuterium solid-state NMR spectra of peptide sites labelled with (2)H3-alanine, whereas (31)P and (2)H solid-state NMR spectra of the lipids furnish valuable information on the macroscopic order and phase properties of the lipid matrix. Using these approaches, peptides and reconstitution protocols can be elaborated in a rational manner, and the analysis of a great number of peptide sequences is reviewed. Finally, a number of polypeptides with membrane topologies that are sensitive to a variety of environmental conditions such as pH, lipid composition and peptide-to-lipid ratio will be presented.

Magainin-AM2 inhibits sucrose-induced hyperglycaemia, oxidative stress, and cognitive dysfunction in Drosophila melanogaster.

Hyperglycaemia-induced oxidative stress plays significant roles in the development of type 2 diabetes and its complications. This study investigates effects of magainin-AM2 on high-sucrose diet induced redox imbalance and cognitive impairment in Drosophila melanogaster. Effects of various concentrations of sucrose, magainin-AM2 or a combination of both agents on mortality, eclosion rate, generation of reactive oxygen and nitrogen species, activities of antioxidant enzymes, thiol system, and markers of cognitive functions in control and treated flies were examined. Results showed that the exposure of flies to high sucrose (30 %-60 % w/w) diet increased mortality rate (38-67 %, P < 0.001) and levels of glucose (1.8-1.9-fold, P < 0.001), hydrogen peroxide (1.4-1.5-fold, P < 0.01) and nitrite/nitrate (1.2-fold, P < 0.01). Decreased levels of total thiol (53-59 %, P < 0.01), non-protein thiols (59-63 %, P < 0.01), catalase activities (39-47 %, P < 0.01-0.05) and glutathione-s-transferase activities (31-43 %, P < 0.01-0.05) were also observed. Magainin-AM2 (0-10 µM/kg diet) did not affect fly mortality rate, levels of hydrogen peroxide and nitrite/nitrate, and activities of catalase and glutathione-s-transferase. However, the peptide produced a dose-dependent increase in total thiol 1.2-1.6-fold, P < 0.001-0.01)and increases non-protein thiol levels at 10 µM/kg diet (2.0-fold, P < 0.01). Magainin-AM2 inhibited sucrose-induced elevation of glucose (55-70 %, P < 0.001), hydrogen peroxide (11-12 %, P < 0.01) and nitrite/nitrate (20-34 %, P < 0.01-0.05). The peptide prevented sucrose-induced reduction in total and non-protein thiols (1.9-2.0-fold, P < 0.05) levels and activities of catalase (2.3-3.1-fold, P < 0.001) and glutathione-s-transferase (1.8-2.8-fold, P < 0.001-0.05). Magainin-AM2 inhibited sucrose-induced reduction in acetylcholinesterase activities (3.6-4.0-fold, P < 0.001), eclosion rate (18 %, P < 0.001) and negative geotaxis (1.3-14-fold, P < 0.001). These results indicate that beneficial actions of magainin-AM2 may also involve the prevention of hyperglycaemia-induced oxidative damage and encourage its further development as an anti-diabetic agent.

Antimicrobial peptide interactions with bacterial cell membranes.

Antimicrobial peptides (AMPs) are potential alternatives for common antibiotics because of their greater activity and efficiency against a broad range of viruses, bacteria, fungi, and parasites. In this project, two antimicrobial peptides including magainin 2 and protegrin 1 with α-helix and ß-sheet secondary structures were selected to investigate their interactions with different lipid bilayers such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine (POPS), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), POPC/POPG (7:3), POPC/POPS (7:3), POPG/POPE(1:3), and POPG/POPE(3:1). The obtained structures of the AMPs illustrated that protegrin 1 cannot maintain its secondary structure in the solution phase in contrast to magainin 2. The head groups of the lipid units play a key role in the stability of the lipid bilayers. The head parts of the lipid membranes by increasing the internal H-bond contribute to membrane compactness. The POPG and POPS units inside the POPC/POPG and POPC/POPS membranes increase the order of the POPC units. The cationic residues of the AMPs form remarkable electrostatic interactions with the negatively charged membrane surfaces, which play a key role in the stabilization process of the peptide secondary structures. The Arg residues of protegrin 1 and the Gly1, Lys4, Lys10, Lys11, Lys14, and Glu19 of the magainin 2 have the most important roles in the complexation process. The values of Gibbs binding energies (ΔG) indicate that the complexation process between AMPs and different bacterial membranes is favorable from the thermodynamic viewpoint and AMPs could form stable complexes with the lipid bilayers. As a result of ΔG values, protegrin 1 forms a more stable complex with POPG/POPE(3:1), while the α-helix has more affinity to the POPG/POPE(1:3) bacterial membranes. Therefore, it can be considered that ß-sheet and α-helix AMPs are more effective against gram-positive and gram-negative bacteria, respectively. The results of this study can provide useful details about the antimicrobial peptide interactions with the bacterial cell, which can be employed for designing new antimicrobial materials with greater efficiency.Communicated by Ramaswamy H. Sarma.

Nanoscale Perturbations of Lipid Bilayers Induced by Magainin 2: Insights from AFM Imaging and Force Spectroscopy.

This study explores the impact of the antimicrobial peptide magainin 2 (Mag2) on lipid bilayers with varying compositions. We employed high-resolution atomic force microscopy (AFM) to reveal a dynamic spectrum of structural changes induced by Mag2. Our AFM imaging unveiled distinct structural alterations in zwitterionic POPC bilayers upon Mag2 exposure, notably the formation of nanoscale depressions within the bilayer surface, which we term as "surface pores" to differentiate them from transmembrane pores. These surface pores are characterized by a limited depth that does not appear to fully traverse the bilayer and reach the opposing leaflet. Additionally, our AFM-based force spectroscopy investigation on POPC bilayers revealed a reduction in bilayer puncture force (FP) and Young's modulus (E) upon Mag2 interaction, indicating a weakening of bilayer stability and increased flexibility, which may facilitate peptide insertion. The inclusion of anionic POPG into POPC bilayers elucidated its modulatory effects on Mag2 activity, highlighting the role of lipid composition in peptide-bilayer interactions. In contrast to surface pores, Mag2 treatment of E. coli total lipid extract bilayers resulted in increased surface roughness, which we describe as a fluctuation-like morphology. We speculate that the weaker cohesive interactions between heterogeneous lipids in E. coli bilayers may render them more susceptible to Mag2-induced perturbations. This could lead to widespread disruptions manifested as surface fluctuations throughout the bilayer, rather than the formation of well-defined pores. Together, our findings of nanoscale bilayer perturbations provide useful insights into the molecular mechanisms governing Mag2-membrane interactions.

Membrane Activity of Melittin and Magainin-I at Low Peptide-to-Lipid Ratio: Different Types of Pores and Translocation Mechanisms.

Antimicrobial peptides (AMPs) are believed to be a prominent alternative to the common antibiotics. However, despite decades of research, there are still no good clinical examples of peptide-based antimicrobial drugs for system application. The main reasons are loss of activity in the human body, cytotoxicity, and low selectivity. To overcome these challenges, a well-established structure-function relationship for AMPs is critical. In the present study, we focused on the well-known examples of melittin and magainin to investigate in detail the initial stages of AMP interaction with lipid membranes at low peptide-to-lipid ratio. By combining the patch-clamp technique with the bioelectrochemical method of intramembrane field compensation, we showed that these peptides interact with the membrane in different ways: melittin inserts deeper into the lipid bilayer than magainin. This difference led to diversity in pore formation. While magainin, after a threshold concentration, formed the well-known toroidal pores, allowing the translocation of the peptide through the membrane, melittin probably induced predominantly pure lipidic pores with a very low rate of peptide translocation. Thus, our results shed light on the early stages of peptide-membrane interactions and suggest new insights into the structure-function relationship of AMPs based on the depth of their membrane insertion.

Beta cell regeneration upon magainin and growth hormone treatment as a possible alternative to insulin therapy.

Insulin therapy, pancreas transplantation and ß cell regeneration are among the suggested treatment strategies for type 1 diabetes. It has been shown that some antimicrobial peptides have the potential to increase insulin release and to improve glucose tolerance, although the mechanism by which they promote the regeneration of damaged pancreatic cells to functional ß-like cells remains unknown. To answer this question, we evaluated the in vivo effects of magainin-AM2 and growth hormone (GH) on the regeneration of streptozotocin (STZ)-damaged mouse pancreas. Treatment with magainin-AM2 and GH ameliorated the effects of STZ on fasting blood glucose and glucose tolerance test values, and also resulted in a significant increase in total cell counts (α and ß) and the number of insulin+ and glucagon+ cells per islet and a decrease in the number of T and B cells. In addition, we observed a 1.43- and 2.21-fold increase in expression of paired box 4, one of the main factors for α to ß-like cell conversion, in normal- and diabetes-treated mice, respectively. Similarly, expression of P-S6 and extracellular signal-regulated kinases 1 and 2, required for cell proliferation/differentiation, increased by 3.27- and 2.19-fold among the diabetes-treated and control diabetic mice, respectively. Furthermore, in all experiments, amelioration of the effects of STZ were greatest upon Mag treatment followed by GH administration. The present in vivo data provide evidence in support of the possibility of pharmaceutical induction of α cell production and their trans-differentiation to functional ß-like cells.