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.

Nanoparticles for Interrogation of Cell Signaling.

Cell functions rely on signal transduction-the cascades of molecular interactions and biochemical reactions that relay extracellular signals to the cell interior. Dissecting principles governing the signal transduction process is critical for the fundamental understanding of cell physiology and the development of biomedical interventions. The complexity of cell signaling is, however, beyond what is accessible by conventional biochemistry assays. Thanks to their unique physical and chemical properties, nanoparticles (NPs) have been increasingly used for the quantitative measurement and manipulation of cell signaling. Even though research in this area is still in its infancy, it has the potential to yield new, paradigm-shifting knowledge of cell biology and lead to biomedical innovations. To highlight this importance, we summarize in this review studies that pioneered the development and application of NPs for cell signaling, from quantitative measurements of signaling molecules to spatiotemporal manipulation of cell signal transduction.

Anisotropic presentation of ligands on cargos modulates degradative function of phagosomes.

Anisotropic arrangement of cell wall components is ubiquitous among bacteria and fungi, but how such functional anisotropy affects interactions between microbes and host immune cells is not known. Here we address this question with regard to phagosome maturation, the process used by host immune cells to degrade internalized microbes. We developed two-faced microparticles as model pathogens that display ligands on only one hemisphere and simultaneously function as fluorogenic sensors for probing biochemical reactions inside phagosomes during degradation. The fluorescent indicator on just one hemisphere gives the particle sensors a moon-like appearance. We show that anisotropic presentation of ligands on particles delays the start of acidification and proteolysis in phagosomes, but does not affect their degradative capacity. Our work suggests that the spatial presentation of ligands on pathogens plays a critical role in modulating the degradation process in phagosomes during host-pathogen interactions.

Single-phagosome imaging reveals that homotypic fusion impairs phagosome degradative function.

Immune cells degrade internalized pathogens in vesicle compartments called phagosomes. Many intracellular bacteria induce homotypic phagosome fusion to survive in host cells, but the fusion interaction between phagosomes and its consequence for phagosome function have scarcely been studied. Here, we characterize homotypic fusion between phagosomes in macrophages and identify how such interactions impact the degradative capacity of phagosomes. By developing a series of particle sensors for measuring biochemical changes of single phagosomes, we show that phagosomes undergo stable fusion, transient "kiss-and-run" fusion, or both in succession. Super-resolution three-dimensional fluorescence microscopy revealed that stably fused phagosomes are connected by membrane "necks" with submicron-sized fusion pores. Furthermore, we demonstrate that, after stable fusion, phagosomes have leaky membranes and thereby impaired degradative functions. Our findings, based on phagosomes that contain synthetic particles, illustrate that homotypic fusion is not exclusive to phagosomes that encapsulate pathogens, as previously believed. The physical process of homotypic fusion is alone sufficient to perturb the degradative functions of phagosomes.

Integrating Electrochemical and Colorimetric Sensors with a Webcam Readout for Multiple Gas Detection.

Multisensor detectors have merits of low cost, compact size, and capability of supplying accurate and reliable information otherwise hard to obtain by any single sensors. They are therefore highly desired in various applications. Despite the advantages and needs, they face great challenges in technique especially when integrating sensors with different sensing principles. To bridge the gap between the demand and technique, we here demonstrated an integration of electrochemical and colorimetric sensors with a webcam readout for multiple gas detection. Designed with two parallel gas channels but independent sensor cells, the dual-sensor detector could simultaneously detect each gas from their gas mixture by analysis of the group photo of the two sensors. Using Ag electro-dissolution as reporter, the bipolar electrochemical sensor achieved quantitative analysis for the first time thanks to application of pulse voltage. The sacrificed Ag layer used in the bipolar electrochemical (EC) sensor was recycled from CD, which further decreased the sensor cost and supplied a new way of CD recycling. The EC O2 sensor response, edge displacement of Ag layer due to electrochemical dissolution, has a linear relationship with O2 concentration ranging from 0 to 30% and has good selectivity to common oxidative gases. The colorimetric NO2 sensor linearly responded to NO2 concentrations ranging from 0 to 230 ppb with low detection limit of 10 ppb, good selectivity, and humidity tolerance. This integration method could be extended to integrating other gas sensors.