Pom-1 and Pom-2 are antimicrobial peptides natively produced by the fresh-water snail Pomacea poeyana. They selectively kill bacteria and yeasts, but present no cytotoxic effects for mammalian cells, and their mode of action is still unclear. Liposome calcein leakage experiments were used to measure permeability effects of both peptides, while Laurdan generalized polarization (GP) was used to determine the effect of the AMPs on apparent membrane fluidity. Only Pom-1 induced dye leakage, with the greatest activity in the bacterial model, following modest activity in the fungal model, and no activity towards the mammalian membrane. Likewise, the greatest effect on membrane fluidity induced by Pom-1 was observed in the bacterial model, with slight changes registered with the fungal model. The effect of the peptide was dosis-dependent. The intrinsic tryptophan fluorescence spectroscopy of Pom-1 indicated that, at a minimum, the hydrophobic N-terminal end of the peptide inserted into all three membranes. Molecular dynamics simulations corroborated the in vitro observations, as Pom-2 did not interact with or perturb membrane properties. Although Pom-1 showed greater free binging energy with the bacterial model, it inserted to a greater depth into the fungal membrane, but without significantly modifying membrane properties. The different capabilities of Pom-1 and Pom-2 to interact with the different bilayers were mainly due to biochemical properties of the peptides such as net charge a neutral pH, hydrophobicity, Bowman index, among others. Pom-1´s secondary structure was stable throughout the simulations, while Pom-2 tended to denature over time. The in-silico analyses suggested that peptide aggregation negatively impacted membrane peptide interaction and subsequent insertion. Conclusively, we present strong evidence that the plasma membrane is the molecular target of Pom-1; The Pom-2 target remains unknown.
Aeromonas salmonicida subsp. salmonicida is a major bacterial pathogen of salmonids in aquaculture, and bacteriophage therapy could provide an alternative to antibiotics for its control. Bacteriophage infection of this Gram-negative bacterium begins at the cell surface and involves interactions with outer membrane components including lipopolysaccharides and surface structures such as the A-layer. Although these interactions influence phage adsorption, their impact on bacterial membrane organization remains poorly understood. Here, we investigated membrane dynamics in three strains differing in envelope architecture and phage sensitivity: AS-R3 (A-layer-positive, phage-sensitive), AS-R5 (A-layer-negative, phage-sensitive), and BIM93 (A-layer-negative, phage-insensitive). We used in vivo 2H solid-state nuclear magnetic resonance combined with phospholipid and fatty acid analyses. Exogenous perdeuterated palmitic acid enabled efficient membrane labelling in intact bacteria without significantly altering the overall lipid composition. While all strains shared similar phospholipid classes, BIM93 displayed a higher proportion of saturated fatty acids and increased membrane order than AS-R3 and AS-R5. Upon exposure to phage SW69-9, membrane order decreased markedly in the sensitive strains, with a pronounced loss of viability in AS-R5. In contrast, BIM93 maintained membrane organization and high viability, whereas AS-R3 showed an intermediate response with significant membrane perturbation despite limited cell lysis. These results indicate that phage-induced membrane perturbations depend on both phage sensitivity and bacterial envelope architecture. More broadly, they suggest that changes in membrane organization during phage exposure are influenced by surface-associated bacterial structures. This study highlights the role of bacterial surface structures and membrane physical properties in shaping phage-host interactions.
While α-tocopherol (αToc) is fundamentally recognized as a membrane-resident antioxidant, its synthetic derivative, α-tocopheryl acetate (αTocAc), has recently gained notoriety as a primary diluent in illicit vaping products associated with E-cigarette or Vaping Use-Associated Lung Injury (EVALI). The pathophysiology of EVALI has been linked to the disruption of pulmonary surfactant (PS) membranes, yet the specific impact on lipid dynamics and mechanical stability remains poorly defined. This study employs avoided level crossing muon spin resonance (ALC-μSR), quasielastic neutron backscattering (QENS), and neutron spin echo (NSE) to quantify the impacts of αToc and αTocAc on 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) and multicomponent PS mimic systems at a physiological temperature of 37 °C. ALC-μSR measurements reveal that αToc restricts local acyl chain dynamics, causing a 50% increase in the motionally averaged dipolar coupling that reduces the tail wobbling cone half-angle (θC). On a mesoscopic scale, QENS demonstrates that low concentrations (2–5 mol%) of αToc and αTocAc suppress lateral lipid diffusivity (Dlat) in pure POPC from a baseline of 0.51×10−10m2/s down to a minimum of 0.35×10−10m2/s, following a non-monotonic trend that recovers near 10 mol%. Concurrently, NSE reveals a pronounced concentration-dependent stiffening of the fluid POPC bilayer, where αTocAc increases the bending modulus (κ) from a baseline of 17.9±0.7kBT up to ≈31kBT at 10 mol%, outstiffening the impact of its natural counterpart. Conversely, the unsaturated fraction of a complex PS mimic maintains a stable dynamic profile (Dlat≈0.35×10−10m2/s), pointing to possible linactant compartmentalization at phase boundaries or clustering. Together, these multiscale findings establish a lipid-centric, biophysical mechanism for EVALI, where αTocAc restricts lateral lipid mobility and over-stiffen the fluid-phase reservoirs of the lung, fundamentally impeding the critical compression–expansion respreading mechanics of pulmonary surfactant required for normal respiration.
Elastin-derived peptides (EDPs), generated during elastin fragmentation in aging and pathological conditions, are widely recognized for their biological activity through interactions with cell-surface receptors. However, despite their hydrophobic character and proximity to membrane-associated receptors, their capacity to directly interact with lipid bilayers has remained largely unexplored. In this study, we investigated the membrane-binding properties of representative elastin hexa and nonapeptides using a combination of molecular dynamics simulations, potential of mean force calculations, and synchrotron radiation circular dichroism spectroscopy. Our results reveal that the hexapeptide displays minimal membrane interactions while nonapeptides bearing the XGXPGXGXG consensus motif exhibit significant and dynamic membrane association. Cholesterol markedly reduces membrane affinity and membrane interaction stabilizes β-turn conformations, particularly type II turns. Together, these findings demonstrate that certain elastin nonapeptides are capable of direct lipid-bilayer interactions, unveiling a previously underappreciated physicochemical dimension of EDP activity. By providing a receptor-independent route through which EDPs could influence cell behavior wherever they accumulate, this membrane-binding capability may contribute to their biological effects and offers a new perspective on elastin fragmentation in aging and disease.
Cholesterol modulates key physicochemical properties of lipid bilayers, including phase behavior, lateral organization, acyl-chain order, and permeability to small solutes. In most phospholipid bilayers, cholesterol can be accommodated in a single liquid-ordered phase up to ~50 mol%; above this saturation limit, excess cholesterol partitions into cholesterol-rich domains and, at higher concentrations, also into cholesterol crystals, while the bilayer fraction remains saturated with cholesterol. Below saturation, cholesterol's principal role is to modulate the physical properties of the lipid bilayer in a composition- and condition-dependent manner. At and above saturation, its dominant role shifts toward buffering these properties against changes in phospholipid composition, thereby stabilizing the bilayer's physical state. This concentration-dependent duality is particularly evident in model membrane systems. In specialized biological membranes with very high cholesterol content, such as lens fiber cell membranes, the stabilizing (preservative) function may predominate. This review outlines how these two functional modes of cholesterol manifest in both model and biological membranes.
