A bactericide peptide changing the static and dilatational surface elasticity properties of zwitterionic lipids at the air-water interface: Relationship with the thermodynamic, structural and morphological properties

The Synthetic Peptide LyeTx I mn∆K, Derived from Lycosa erythrognatha Spider Toxin, Is Active against Methicillin-Resistant Staphylococcus aureus (MRSA) In Vitro and In Vivo

The urgent global health challenge posed by methicillin-resistant Staphylococcus aureus (MRSA) infections demands effective solutions. Antimicrobial peptides (AMPs) represent promising tools of research of new antibacterial agents and LyeTx I mn∆K, a short synthetic peptide based on the Lycosa erythrognatha spider venom, is a good representative. This study focused on analyzing the antimicrobial activities of LyeTx I mn∆K, including minimum inhibitory and bactericidal concentrations, synergy and resensitization assays, lysis activity, the effect on biofilm, and the bacterial death curve in MRSA. Additionally, its characterization was conducted through isothermal titration calorimetry, dynamic light scattering, calcein release, and finally, efficacy in a mice wound model. The peptide demonstrates remarkable efficacy against planktonic cells (MIC 8-16 µM) and biofilms (>30% of inhibition) of MRSA, and outperforms vancomycin in terms of rapid bactericidal action and anti-biofilm effects. The mechanism involves significant membrane damage. Interactions with bacterial model membranes, including those with lysylphosphatidylglycerol (LysylPOPG) modifications, highlight the versatility and selectivity of this compound. Also, the peptide has the ability to sensitize resistant bacteria to conventional antibiotics, showing potential for combinatory therapy. Furthermore, using an in vivo model, this study showed that a formulated gel containing the peptide proved superior to vancomycin in treating MRSA-induced wounds in mice. Together, the results highlight LyeTx I mnΔK as a promising prototype for the development of effective therapeutic strategies against superficial MRSA infections.

Insight into the Molecular Mechanism of Surface Interactions of Phosphatidylcholines─Langmuir Monolayer Study Complemented with Molecular Dynamics Simulations

Mutual interactions between components of biological membranes are pivotal for maintaining their proper biophysical properties, such as stability, fluidity, or permeability. The main building blocks of biomembranes are lipids, among which the most important are phospholipids (mainly phosphatidylcholines (PCs)) and sterols (mainly cholesterol). Although there is a plethora of reports on interactions between PCs, as well as between PCs and cholesterol, their molecular mechanism has not yet been fully explained. Therefore, to resolve this issue, we carried out systematic investigations based on the classical Langmuir monolayer technique complemented with molecular dynamics simulations. The studies involved systems containing 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) analogues possessing in the structure one or two polar functional groups similar to those of DPPC. The interactions and rheological properties of binary mixtures of DPPC analogues with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and cholesterol were compared with reference systems (DPPC/POPC and DPPC/cholesterol). This pointed to the importance of the ternary amine group in PC/cholesterol interactions, while in PC mixtures, the phosphate group played a key role. In both cases, the esterified glycerol group had an effect on the magnitude of interactions. The obtained results are crucial for establishing structure-property relationships as well as for designing substitutes for natural lipids.

Growth Inhibition of Sulfate-Reducing Bacteria during Gas and Oil Production Using Novel Schiff Base Diquaternary Biocides: Synthesis, Antimicrobial, and Toxicological Assessment

Upstream crude oil production equipment is always exposed to destruction damagingly which is caused by sulfate-reducing bacterium (SRB) activities that produce H2S gas, which leads to increased metal corrosion (bio-fouling) rates and inflicts effective infrastructure damage. Hence, oil and gas reservoirs must be injected with biocides and inhibitors which still offer the foremost protection against harmful microbial activity. However, because of the economic and environmental risks associated with biocides, the oil and gas sectors improve better methods for their usage. This work describes the synthesis and evaluation of the biological activities as the cytotoxicity and antimicrobial properties of a series of diquaternary cationic biocides that were studied during the inhibition of microbial biofilms. The prepared diquaternary compound was synthesized by coupling vanillin and 4-aminoantipyrene to achieve the corresponding Schiff base, followed by a quaternization reaction using 1,6-bromohexane, 1,8-bromooctane, and 1,12-bromododecane. The increase of their alkyl chain length from 6 to 12 methylene groups increased the obtained antimicrobial activity and cytotoxicity. Antimicrobial efficacies of Q1-3 against various biofilm-forming microorganisms, including bacteria and fungi, were examined utilizing the diameter of inhibition zone procedures. The results revealed that cytotoxic efficacies of Q1-3 were significantly associated mainly with maximum surface excess and interfacial characteristics. The cytotoxic efficiencies of Q1-3 biocides demonstrated promising results due to their comparatively higher efficacies against SRB. Q3 exhibited the highest cytotoxic biocide against the gram +ve, gram -ve, and SRB species according to the inhibition zone diameter test. The toxicity of the studied microorganisms depended on the nature and type of the target microorganism and the hydrophobicity of the biocide molecules. Cytotoxicity assessment and antimicrobial activity displayed increased activity by the increase in their alkyl chain length.

Influence of cytochrome P450 3A4 and membrane lipid composition on doxorubicin activity

Drug resistance is known to depend on the interactions with cell membranes and other molecules such as human cytochromes P450 (CYPs) which are anchored on the endoplasmic reticulum (ER) membrane and involved in the metabolism of anticancer drugs. In this study, we determined the influence from cytochrome P450 3A4 (CYP3A4) on the interaction between the drug doxorubicin (DOX) and Langmuir monolayers mimicking cell membranes. The lipid composition was varied by changing the relative concentrations of cholesterol (Chol), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), and L-α-phosphatidylinositol (PI). Three compositions were studied in detail which represented a healthy cell membrane and cancerous cell membranes. DOX induced an expansion in the surface pressure isotherms for all monolayers, with stronger effect for the composition of cancerous cell with a high Chol content, thus confirming the relevance of lipid composition. This effect decreased considerably when CYP3A4 was incorporated with the formation of CYP3A4-DOX complexes, according to results from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) measurements. Taken together, these results support the hypothesis of CYP3A4 being involved in drug resistance, which may be exploited to design strategies to enhance chemotherapy efficacy.

Biological activity of pectic polysaccharides investigated through biomembrane models formed at the air-water interface

Pectin, a polysaccharide with potential bioactivity, was inserted in the aqueous subphase of monolayers of the selected lipids DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and DPPE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine), representing mammalian and bacterial membranes, respectively. Pectin condensed both monolayers but made the DPPC monolayer more fluid, while for DPPE, it made its monolayer more rigid, as detected with dynamic interfacial rheology. Complementary data using surface potential, infrared spectroscopy, and Brewster angle microscopy also showed distinctive effects of pectin on DPPE and DPPC. We believe these data can be correlated with the action of this polysaccharide with biological lipidic surfaces with different polar heads, which may be relevant, generally speaking, to understanding the molecular mechanism of this bioactive compound for pharmaceutical purposes.

Roles of key residues and lipid dynamics reveal pHLIP-membrane interactions at intermediate pH

The pH-low insertion peptide (pHLIP) and its analogs sense the microenvironmental pH variations in tumorous cells and serve as useful anticancer drug deliveries. The pHLIP binds peripherally to membranes and adopts random coil conformation at the physiological pH. The peptide switches from random coil to α-helical conformation and inserts unidirectionally into membrane bilayers when pH drops below a critical transition value that has been routinely determined by the Trp fluorescence spectroscopy. Recent high-resolution studies using solid-state NMR spectroscopy revealed the presence of thermodynamically stable intermediate states of membrane-associated pHLIP around the fluorescence-based transition pH-value. However, the molecular structural features and their mechanistic roles of these intermediate states in the pH-driven membrane insertion process of pHLIP remain largely unknown. This work utilizes solid-state NMR spectroscopy to explore 1) the mechanistic roles of key proline and arginine residues within the pHLIP sequence at intermediate pH-values, and 2) the changes in lipid dynamics at intermediate pH-values in multiple types of model bilayers with anionic phospholipid and/or cholesterol. Our results demonstrate several molecular structural and dynamics changes at around the transition pH-values, including the isomerization of proline-threonine backbone configuration, breaking of arginine-aspartic acid salt bridge and the formation of arginine-lipid interactions, and a universal decreasing of dynamics in lipid headgroups and alkyl chains. Overall, the outcomes provide important insights on the molecular interactions between pHLIP and membrane bilayers at intermediate pH-values and, therefore, prompt the understanding of pH-driven membrane insertion process of this anticancer drug-delivering peptide.

Interaction of Human β Defensin Type 3 (hBD-3) with Different PIP2-Containing Membranes, a Molecular Dynamics Simulation Study

Human β defensin type 3 (hBD-3) is a cysteine-rich small antibacterial peptide. It belongs to the human innate immune system. hBD-3 has six cysteine residues, which form three pairs of disulfide bonds, and those bonds break in the reducing condition. It is known that hBD-3 can interact with bacterial membrane, and even eukaryotic cell membrane, which has a low concentration of phosphatidylinositol 4,5-bisphosphate (PIP2) lipids. PIP2 is a vital component in cell membranes and has been found to play important roles during antimicrobial peptide (AMP) interaction with membranes. To understand the functional mechanism of hBD-3 interacting with PIP2-containing membranes, the binding structures of hBD-3 on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers mixed with 10% of PIP2 were predicted using two kinds of methods. The first one is by placing the hBD-3 monomer in different orientations above the POPC + 10%PIP2 membrane to set up five different initial simulation systems and performing long-term simulations on each to predict the most stable binding structure. It was found that hBD-3 analogue binds on the mixed lipid membrane on the two loop regions. The second method is by running long-term simulations on one or nine hBD-3 dimers binding on POPC mixed with 10%PIP2 lipid bilayer starting from the solid-state NMR (ssNMR)-suggested orientation. The dimer dissociated, and the most stable binding of hBD-3 in wild-type on the mixed membrane is also through the two loop regions, which agrees with the prediction from both the first method and the lipid self-assembly result. The PIP2 lipids can form long-lasting hydrogen bonds with positively charged residues such as Arg and Lys on hBD-3, thus forming clusters with hBD-3. As a comparison, hBD-3 dimers binding with a combined bilayer having 1,2-palmitoyl-oleoyl-sn-glycero-3-phosphoserine (POPS) on the upper and POPC on the lower leaflets and the combined POPS + POPC bilayer mixing with 10%PIP2 were also studied. The long-term simulation result shows that hBD-3 can bind with the heads of negatively charged POPS and PIP2 lipids and form hydrogen bonds. The stable binding sites of hBD-3 on PIP2 or POPS mixed bilayers are still on the two loop regions. On the combined POPS + POPC mixed with 10%PIP2 bilayer, the binding of hBD-3 with PIP2 lipids became less stable and fewer because of the competition of binding with the POPS lipids. Besides that, binding with hBD-3 can decrease the membrane thickness of the POPC + PIP2, POPS + POPC, and POPS + POPC + PIP2 bilayers and make POPS and PIP2 lipids more flexible based on the order parameter calculations. Our results supply molecular insight on AMP binding with different membranes and can help understand the functional mechanism of hBD-3 disrupting PIP2-containing membranes.

Membrane Association Modes of Natural Anticancer Peptides: Mechanistic Details on Helicity, Orientation, and Surface Coverage

Anticancer peptides (ACPs) could potentially offer many advantages over other cancer therapies. ACPs often target cell membranes, where their surface mechanism is coupled to a conformational change into helical structures. However, details on their binding are still unclear, which would be crucial to reach progress in connecting structural aspects to ACP action and to therapeutic developments. Here we investigated natural helical ACPs, Lasioglossin LL-III, Macropin 1, Temporin-La, FK-16, and LL-37, on model liposomes, and also on extracellular vesicles (EVs), with an outer leaflet composition similar to cancer cells. The combined simulations and experiments identified three distinct binding modes to the membranes. Firstly, a highly helical structure, lying mainly on the membrane surface; secondly, a similar, yet only partially helical structure with disordered regions; and thirdly, a helical monomeric form with a non-inserted perpendicular orientation relative to the membrane surface. The latter allows large swings of the helix while the N-terminal is anchored to the headgroup region. These results indicate that subtle differences in sequence and charge can result in altered binding modes. The first two modes could be part of the well-known carpet model mechanism, whereas the newly identified third mode could be an intermediate state, existing prior to membrane insertion.