Membrane poration, wrinkling, and compression: deformations of lipid vesicles induced by amphiphilic Janus nanoparticles

Targeting the Weak Spot: Preferential Disruption of Bacterial Poles by Janus Nanoparticles

The interaction between nanoparticles (NPs) and bacterial cell envelopes is crucial for designing effective antibacterial materials against multi-drug-resistant pathogens. However, the current understanding assumes a uniform bacterial cell wall. This study challenges that assumption by investigating how bacterial cell wall curvature impacts antibacterial NP action. Focusing on Janus NPs, which feature segregated hydrophobic and polycationic ligands and previously demonstrated high efficacy against diverse bacteria, we found that these NPs preferentially target and disrupt bacterial poles. Experimental and computational approaches reveal that curvature at E. coli poles induces conformational changes in lipopolysaccharide (LPS) polymers on the outer membrane, exposing underlying lipids for NP-mediated disruption. We establish that curvature-induced targeting by Janus NPs depends on the outer membrane composition and is most pronounced at physiologically relevant LPS densities. This work demonstrates that high-curvature regions of bacterial cell walls are "weak spots" for Janus NPs, thereby aiding the development of more effective targeted therapies.

Cholesterol-Dependent Membrane Deformation by Metastable Viral Capsids Facilitates Entry

Nonenveloped viruses employ unique entry mechanisms to breach and infect host cells. Understanding these mechanisms is crucial for developing antiviral strategies. Prevailing perspective suggests that nonenveloped viruses release membrane pore-forming peptides to breach host membranes. However, the precise involvement of the viral capsid in this entry remains elusive. Our study presents direct observations elucidating the dynamically distinctive steps through which metastable reovirus capsids disrupt host lipid membranes as they uncoat into partially hydrophobic intermediate particles. Using both live cells and model membrane systems, our key finding is that reovirus capsids actively deform and permeabilize lipid membranes in a cholesterol-dependent process. Unlike membrane pore-forming peptides, these metastable viral capsids induce more extensive membrane perturbations, including budding, bridging between adjacent membranes, and complete rupture. Notably, cholesterol enhances subviral particle adsorption, resulting in the formation of pores equivalent to the capsid size. This cholesterol dependence is attributed to the lipid condensing effect, particularly prominent at an intermediate cholesterol level. Furthermore, our results reveal a positive correlation between membrane disruption extent and efficiency of viral variants in establishing infection. This study unveils the crucial role of capsid-lipid interaction in nonenveloped virus entry, providing new insights into how cholesterol homeostasis influences virus infection dynamics.

Cholesterol-Dependent Membrane Deformation by Metastable Viral Capsids Facilitates Entry

Non-enveloped viruses employ unique entry mechanisms to breach and infect host cells. Understanding these mechanisms is crucial for developing antiviral strategies. Prevailing perspective suggests that non-enveloped viruses release membrane lytic peptides to breach host membranes. However, the precise involvement of the viral capsid in this entry remains elusive. Our study presents direct observations elucidating the dynamically distinctive steps through which metastable reovirus capsids disrupt host lipid membranes as they uncoat into partially hydrophobic intermediate particles. Using both live cells and model membrane systems, our key finding is that reovirus capsids actively deform and permeabilize lipid membranes in a cholesterol-dependent process. Unlike membrane lytic peptides, these metastable viral capsids induce more extensive membrane perturbations, including budding, bridging between adjacent membranes, and complete rupture. Notably, cholesterol enhances subviral particle adsorption, resulting in the formation of pores equivalent to the capsid size. This cholesterol dependence is attributed to the lipid condensing effect, particularly prominent at intermediate cholesterol level. Furthermore, our results reveal a positive correlation between membrane disruption extent and efficiency of viral variants in establishing infection. This study unveils the crucial role of capsid-lipid interaction in non-enveloped virus entry, providing new insights into how cholesterol homeostasis influences virus infection dynamics.

Gold nanoparticle adsorption alters the cell stiffness and cell wall bio-chemical landscape of Candida albicans fungal cells

HYPOTHESIS

Nanomaterials have been extensively investigated for a wide range of biomedical applications, including as antimicrobial agents, drug delivery vehicles, and diagnostic devices. The commonality between these biomedical applications is the necessity for the nanoparticle to interact with or pass through the cellular wall and membrane. Cell-nanomaterial interactions/uptake can occur in various ways, including adhering to the cell wall, forming aggregates on the surface, becoming absorbed within the cell wall itself, or transversing into the cell cytoplasm. These interactions are common to mammalian cells, bacteria, and yeast cells. This variety of interactions can cause changes to the integrity of the cell wall and the cell overall, but the precise mechanisms underpinning such interactions remain poorly understood. Here, we investigate the interaction between commonly investigated gold nanoparticles (AuNPs) and the cell wall/membrane of a model fungal cell to explore the general effects of interaction and uptake.

EXPERIMENTS

The interactions between 100 nm citrate-capped AuNPs and the cell wall of Candida albicans fungal cells were studied using a range of advanced microscopy techniques, including atomic force microscopy, confocal laser scanning microscopy, scanning electron microscopy, transmission electron microscopy, and synchrotron-FTIR micro-spectroscopy.

FINDINGS

In most cases, particles adhered on the cell surface, although instances of particles being up-taken into the cell cytoplasm and localised within the cell wall and membrane were also observed. There was a measurable increase in the stiffness of the fungal cell after AuNPs were introduced. Analysis of the synchrotron-FTIR data showed significant changes in spectral features associated with phospholipids and proteins after exposure to AuNPs.

Computational investigation on lipid bilayer disruption induced by amphiphilic Janus nanoparticles: combined effect of Janus balance and charged lipid concentration

Janus nanoparticles (NPs) with charged/hydrophobic compartments have garnered attention for their potential antimicrobial activity. These NPs have been shown to disrupt lipid bilayers in experimental studies, yet the underlying mechanisms of this disruption at the particle-membrane interface remain unclear. To address this knowledge gap, the present study conducts a computational investigation to systematically examine the disruption of lipid bilayers induced by amphiphilic Janus NPs. The focus of this study is on the combined effects of the hydrophobicity of the Janus NP, referred to as the Janus balance, defined as the ratio of hydrophilic to hydrophobic surface coverage, and the concentration of charged phospholipids on the interactions between Janus NPs and lipid bilayers. Computational simulations were conducted using a coarse-grained molecular dynamics (MD) approach. The results of these MD simulations reveal that while the area change of the bilayer increases monotonically with the Janus balance, the effect of charged lipid concentration in the membrane is not easy to be predicted. Specifically, it was found that the concentration of negatively charged lipids is directly proportional to the intensity of membrane disruption. Conversely, positively charged lipids have a negligible effect on membrane defects. This study provides molecular insights into the significant role of Janus balance in the disruption of lipid bilayers by Janus NPs and supports the selectivity of Janus NPs for negatively charged lipid membranes. Furthermore, the anisotropic properties of Janus NPs were found to play a crucial role in their ability to disrupt the membrane via the combination of hydrophobic and electrostatic interactions. This finding is validated by testing the current Janus NP design on a bacterial membrane-mimicking model. This computational study may serve as a foundation for further studies aimed at optimizing the properties of Janus NPs for specific antimicrobial applications.

Methods to mechanically perturb and characterize GUV-based minimal cell models

Cells shield organelles and the cytosol via an active boundary predominantly made of phospholipids and membrane proteins, yet allowing communication between the intracellular and extracellular environment. Micron-sized liposome compartments commonly known as giant unilamellar vesicles (GUVs) are used to model the cell membrane and encapsulate biological materials and processes in a cell-like confinement. In the field of bottom-up synthetic biology, many have utilized GUVs as substrates to study various biological processes such as protein-lipid interactions, cytoskeletal assembly, and dynamics of protein synthesis. Like cells, it is ideal that GUVs are also mechanically durable and able to stay intact when the inner and outer environment changes. As a result, studies have demonstrated approaches to tune the mechanical properties of GUVs by modulating membrane composition and lumenal material property. In this context, there have been many different methods developed to test the mechanical properties of GUVs. In this review, we will survey various perturbation techniques employed to mechanically characterize GUVs.

Behavior of Citrate-Capped Ultrasmall Gold Nanoparticles on a Supported Lipid Bilayer Interface at Atomic Resolution

Nanomaterials have the potential to transform biological and biomedical research, with applications ranging from drug delivery and diagnostics to targeted interference of specific biological processes. Most existing research is aimed at developing nanomaterials for specific tasks such as enhanced biocellular internalization. However, fundamental aspects of the interactions between nanomaterials and biological systems, in particular, membranes, remain poorly understood. In this study, we provide detailed insights into the molecular mechanisms governing the interaction and evolution of one of the most common synthetic nanomaterials in contact with model phospholipid membranes. Using a combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations, we elucidate the precise mechanisms by which citrate-capped 5 nm gold nanoparticles (AuNPs) interact with supported lipid bilayers (SLBs) of pure fluid (DOPC) and pure gel-phase (DPPC) phospholipids. On fluid-phase DOPC membranes, the AuNPs adsorb and are progressively internalized as the citrate capping of the NPs is displaced by the surrounding lipids. AuNPs also interact with gel-phase DPPC membranes where they partially embed into the outer leaflet, locally disturbing the lipid organization. In both systems, the AuNPs cause holistic perturbations throughout the bilayers. AFM shows that the lateral diffusion of the particles is several orders of magnitude smaller than that of the lipid molecules, which creates some temporary scarring of the membrane surface. Our results reveal how functionalized AuNPs interact with differing biological membranes with mechanisms that could also have implications for cooperative membrane effects with other molecules.

Modes of adhesion of two Janus nanoparticles on the outer or inner side of lipid vesicles

Using molecular dynamics simulations of a coarse-grained model, in conjunction with the weighted histogram analysis method, the adhesion modes of two spherical Janus nanoparticles (NPs) on the outer or inner side of lipid vesicles are explored. In particular, the effects of the area fraction, J, of the NPs that interact attractively with lipid head groups, the adhesion strength and the size of the NPs on their adhesion modes are investigated. The NPs are found to exhibit two main modes of adhesion when adhered to the outer side of the vesicle. In the first mode, which occurs at relatively low values of J, the NPs are apart from each other. In the second mode, which occurs at higher values of J, the NPs form an in-plane dimer. Janus NPs, which adhere to the inner side of the vesicle, are always found to be apart from each other, regardless of the value of J and their diameter.

Uptake and toxicity of polystyrene micro/nanoplastics in gastric cells: Effects of particle size and surface functionalization

Toxicity of micro or nanoplastics (MP/NP) in aquatic life is well-documented, however, information about the consequences of exposure to these particles in terrestrial species is scarce. This study was used to evaluate the uptake and/or toxicity of polystyrene MP/NP in human gastric cells, comparing doses, particle sizes (50, 100, 200, 500, 1000 or 5000 nm) and surface functionalization (aminated, carboxylated or non-functionalized). In general, the uptake of 50 nm particles was significantly higher than 1000 nm particles. Among the 50 nm particles, the aminated particles were more avidly taken up by the cells and were cytotoxic at a lower concentration (≥ 7.5 μg/mL) compared to same sized carboxylated or non-functionalized particles (≥ 50 μg/mL). High toxicity of 50 nm aminated particles corresponded well with significantly high rates of apoptosis-necrosis induced by these particles in 4 h (29.2% of total cells) compared to all other particles (≤ 16.8%). The trend of apoptosis-necrosis induction by aminated particles in 4 h was 50 > 5000 > 1000 > 500 > 200 > 100 nm. The 50 nm carboxylated or non-functionalized particles also induced higher levels of apoptosis-necrosis in the cells compared to 100, 1000 and 5000 nm particles with same surface functionalization but longer exposure (24 h) to 50 nm carboxylated or non-functionalized particles significantly (p<0.0001) increased apoptosis-necrosis in the cells. The study demonstrated that the toxicity of MP/NP to gastric cells was dependent on particle size, dose surface functionalization and exposure period.

Designing amphiphilic Janus nanoparticles with tunable lipid raft affinity via molecular dynamics simulation

Due to the differential interactions among lipids and proteins, the plasma membrane can segregate into a series of functional nanoscale membrane domains ("lipid rafts"), which are essential in multiple biological processes such as signaling transduction, protein trafficking and endocytosis. On the other hand, Janus nanoparticles (NPs) have shown great promise in various biomedical applications due to their asymmetric characteristics and can integrate different surface properties and thus synergetic functions. Hence, in this work, we aim to design an amphiphilic Janus NP to target and regulate lipid rafts via tuning its surface ligand amphiphilicity using coarse-grained molecular dynamics (MD) simulations. Our μs-scale free coarse-grained MD simulations as well as umbrella sampling free energy calculations indicated that the hydrophobicity of the hydrophobic surface ligands not only determined the lateral membrane partitioning thermodynamics of Janus NPs in phase-separated lipid membranes, but also the difficulty in their insertion into different membrane domains of the lipid membrane. These two factors jointly regulated the lipid raft affinity of Janus NPs. Meanwhile, the hydrophilicity of the hydrophilic surface ligands could affect the insertion ability of Janus NPs. Besides, the ultra-small size could ensure the membrane-bound behavior of Janus NPs without disrupting the overall structure and phase separation kinetics of the lipid membrane. These results may provide valuable insights into the design of functional NPs targeting and controllably regulating lipid rafts.

Nanocapsule designs for antimicrobial resistance

The pressing need of new antimicrobial products is growing stronger, particularly because of widespread antimicrobial resistance, endangering our ability to treat common infections. The recent coronavirus pandemic has dramatically highlighted the necessity of effective antibacterial and antiviral protection. This work explores at the molecular level the mechanism of action of antibacterial nanocapsules assembled in virus-like particles, their stability and their interaction with mammal and antimicrobial model membranes. We use Molecular Dynamics with force-fields of different granularity and protein design strategies to study the stability, self-assembly and membrane poration properties of these nanocapsules.

Exploration and insights into the cellular internalization and intracellular fate of amphiphilic polymeric nanocarriers

The beneficial or deleterious effects of nanomedicines emerge from their complex interactions with intracellular pathways and their subcellular fate. Moreover, the dynamic nature of plasma membrane accounts for the movement of these nanocarriers within the cell towards different organelles thereby not only influencing their pharmacokinetic and pharmacodynamic properties but also bioavailability, therapeutic efficacy and toxicity. Therefore, an in-depth understanding of underlying parameters controlling nanocarrier endocytosis and intracellular fate is essential. In order to direct nanoparticles towards specific sub-cellular organelles the physicochemical attributes of nanocarriers can be manipulated. These include particle size, shape and surface charge/chemistry. Restricting the particle size of nanocarriers below 200 nm contributes to internalization via clathrin and caveolae mediated pathways. Similarly, a moderate negative surface potential confers endolysosomal escape and targeting towards mitochondria, endoplasmic reticulum (ER) and Golgi. This review aims to provide an insight into these physicochemical attributes of nanocarriers fabricated using amphiphilic graft copolymers affecting cellular internalization. Fundamental principles understood from experimental studies have been extrapolated to draw a general conclusion for the designing of optimized nanoparticulate drug delivery systems and enhanced intracellular uptake via specific endocytic pathway.