Robust Photoelectric Biomolecular Switch at a Microcavity-Supported Lipid Bilayer

Spontaneous Vibrations and Stochastic Resonance of Short Oligomeric Springs

There is growing interest in molecular structures that exhibit dynamics similar to bistable mechanical systems. These structures have the potential to be used as two-state operating units for various functional purposes. Particularly intriguing are the bistable systems that display spontaneous vibrations and stochastic resonance. Previously, via molecular dynamics simulations, it was discovered that short pyridine-furan springs in water, when subjected to stretching with power loads, exhibit the bistable dynamics of a Duffing oscillator. In this study, we extend these simulations to include short pyridine-pyrrole and pyridine-furan springs in a hydrophobic solvent. Our findings demonstrate that these systems also display the bistable dynamics, accompanied by spontaneous vibrations and stochastic resonance activated by thermal noise.

Leaflet by Leaflet Synergistic Effects of Antimicrobial Peptides on Bacterial and Mammalian Membrane Models

Antimicrobial peptides (AMPs) offer significant hope in the fight against antibiotic resistance. Operating via a mechanism different from that of antibiotics, they target the microbial membrane and ideally should damage it without impacting mammalian cells. Here, the interactions of two AMPs, magainin 2 and PGLa, and their synergistic effects on bacterial and mammalian membrane models were studied using electrochemical impedance spectroscopy, atomic force microscopy (AFM), and fluorescence correlation spectroscopy. Toroidal pore formation was observed by AFM when the two AMPs were combined, while individually AMP effects were confined to the exterior leaflet of the bacterial membrane analogue. Using microcavity-supported lipid bilayers, the diffusivity of each bilayer leaflet could be studied independently, and we observed that combined, the AMPs penetrate both leaflets of the bacterial model but individually each peptide had a limited impact on the proximal leaflet of the bacterial model. The impact of AMPs on a ternary, mammalian mimetic membrane was much weaker.

Role of phosphatidylserine in amyloid-beta oligomerization at asymmetric phospholipid bilayers

Amyloid-beta (Aβ_1-42) aggregation triggers neurotoxicity and is linked to Alzheimer's disease. Aβ_1-42 oligomers, rather than extended fibrils, adhere to the cell membrane, causing cell death. Phosphatidylserine (PS), an anionic phospholipid, is prevalent in neuronal membranes (< 20 molar percentage) and, while isolated to the cytoplasmic leaflet of the membrane in healthy cells, its exposure in apoptotic cells and migration to exoplasmic leaflet is triggered by oxidative damage to the membrane. It is widely believed that PS plays a crucial role in the Aβ peptide interaction in the membranes of neuronal cells. However, due to the complexity of the cell membrane, it can be challenging to address molecular level understanding of the PS-Aβ binding and oligomerization processes. Herein, we use microcavity supported lipid bilayers (MSLBs) to analyse PS and Aβ_1-42 binding, oligomer formation, and membrane damage. MSLBs are a useful model to evaluate protein-membrane interactions because of their cell-like dual aspect fluidity, their addressability and compositional versatility. We used electrochemical impedance spectroscopy (EIS) and confocal fluorescence microscopy to compare the impact of Aβ_1-42 on simple zwitterioinic membrane, dioleoylphosphatidylcholine (DOPC), with MSLBs comprised of transversally asymmetric binary DOPC and dioleoylphosphatidylserine (DOPS). Monomeric Aβ_1-42 adsorbs weakly to the pristine zwitterionic DOPC membrane without aggregation. Using a membrane integrity test, with pyranine trapped within the cavities beneath the membrane, Aβ_1-42 exposure did not result in pyranine leakage, indicating that DOPC membranes were intact. When 10 mol% DOPS was doped asymmetrically into the membrane's outer leaflet, oligomerization of Aβ_1-42 monomer was evident in EIS and atomic force microscopy (AFM), and confocal imaging revealed that membrane damage, resulted in extensive pyranine leakage from the pores. The effects were time, and DOPS and Aβ_1-42 concentration-dependent. Membrane pore formation was visible within 30 minutes, and oligomerization, membrane-oligomer multilayer, and Aβ_1-42 fibril formation evident over 3 to 18 hours. In asymmetric membranes with DOPS localized to the lower leaflet, optothermally (laser induced) damage increased local DOPS concentrations at the distal leaflet, promoting Aβ_1-42 aggregation.

A cell free biomembrane platform for multimodal study of influenza virus hemagglutinin and for evaluation of entry-inhibitors against hemagglutinin

Seasonal periodic pandemics and epidemics caused by Influenza A viruses (IAVs) are associated with high morbidity and mortality worldwide. They are frequent and unpredictable in severity so there is a need for biophysical platforms that can be used to provide both mechanistic insights into influenza virulence and its potential treatment by anti-IAV agents. Host membrane viral association through the glycoprotein hemagglutinin (HA) of IAVs is one of the primary steps in infection. HA is thus a potential target for drug discovery and development against influenza. Deconvolution of the multivalent interactions of HA at the interfaces of the host cell membrane can help unravel therapeutic targets. In this contribution, we reported the effect of a multivalent HA glycoprotein association on various glycosphingolipid receptors (GD1a, GM3, GM1) doped asymmetrically into an artificial host membrane spanned across an aqueous filled microcavity array. The extent of HA association and its impact on membrane resistance, capacitance, and diffusivity was measured using highly sensitive electrochemical impedance spectroscopy (EIS) and fluorescence lifetime correlation spectroscopy (FLCS). Furthermore, we investigated the inhibition of the influenza HA glycoprotein association with the host mimetic surface by natural and synthetic sialic acid-based inhibitors (sialic acid, Siaα2,3-GalOMe, FB127, 3-sialyl lactose) using electrochemical impedance spectroscopy and observe that while all inhibit, they do not prevent host binding. Overall, the work demonstrates the platform provides a label-free screening platform for the biophysical evaluation of new inhibitors in the development of potential therapeutics for IAV infection prevention and treatment.

Short Pyridine-Furan Springs Exhibit Bistable Dynamics of Duffing Oscillators

The intensive development of nanodevices acting as two-state systems has motivated the search for nanoscale molecular structures whose dynamics are similar to those of bistable mechanical systems, such as Euler arches and Duffing oscillators. Of particular interest are the molecular structures capable of spontaneous vibrations and stochastic resonance. Recently, oligomeric molecules that were a few nanometers in size and exhibited the bistable dynamics of an Euler arch were identified through molecular dynamics simulations of short fragments of thermo-responsive polymers subject to force loading. In this article, we present molecular dynamics simulations of short pyridine-furan springs a few nanometers in size and demonstrate the bistable dynamics of a Duffing oscillator with thermally-activated spontaneous vibrations and stochastic resonance.

Shorter Alkyl Chains Enhance Molecular Diffusion and Electron Transfer Kinetics between Photosensitisers and Catalysts in CO2 -Reducing Photocatalytic Liposomes

Covalent functionalisation with alkyl tails is a common method for supporting molecular catalysts and photosensitisers onto lipid bilayers, but the influence of the alkyl chain length on the photocatalytic performances of the resulting liposomes is not well understood. In this work, we first prepared a series of rhenium-based CO₂ -reduction catalysts [Re(4,4'-(C_n H_2n+1 )₂ -bpy)(CO)₃ Cl] (ReC_n ; 4,4'-(C_n H_2n+1 )₂ -bpy=4,4'-dialkyl-2,2'-bipyridine) and ruthenium-based photosensitisers [Ru(bpy)₂ (4,4'-(C_n H_2n+1 )₂ -bpy)](PF₆ )₂ (RuC_n ) with different alkyl chain lengths (n=0, 9, 12, 15, 17, and 19). We then prepared a series of PEGylated DPPC liposomes containing RuC_n and ReC_n , hereafter noted C_n , to perform photocatalytic CO₂ reduction in the presence of sodium ascorbate. The photocatalytic performance of the C_n liposomes was found to depend on the alkyl tail length, as the turnover number for CO (TON) was inversely correlated to the alkyl chain length, with a more than fivefold higher CO production (TON=14.5) for the C₉ liposomes, compared to C₁₉ (TON=2.8). Based on immobilisation efficiency quantification, diffusion kinetics, and time-resolved spectroscopy, we identified the main reason for this trend: two types of membrane-bound RuC_n species can be found in the membrane, either deeply buried in the bilayer and diffusing slowly, or less buried with much faster diffusion kinetics. Our data suggest that the higher photocatalytic performance of the C₉ system is due to the higher fraction of the more mobile and less buried molecular species, which leads to enhanced electron transfer kinetics between RuC₉ and ReC₉ .