SARS‐CoV‐2 spike protein (S) binds to human angiotensin‐converting enzyme 2 (hACE2), allowing virus to dock on cell membrane follow by viral entry. Here, we use high‐speed atomic force microscopy (HS‐AFM) for real‐time visualization of S, and its interaction with hACE2 and small extracellular vesicles (sEVs). Results show conformational heterogeneity of S, flexibility of S stalk and receptor‐binding domain (RBD), and pH/temperature‐induced conformational change of S. S in an S‐ACE2 complex appears as an all‐RBD up conformation. The complex acquires a distinct topology upon acidification. S and S2 subunit demonstrate different membrane docking mechanisms on sEVs. S‐hACE2 interaction facilitates S to dock on sEVs, implying the feasibility of ACE2‐expressing sEVs for viral neutralization. In contrary, S2 subunit docks on lipid layer and enters sEV using its fusion peptide, mimicking the viral entry scenario. Altogether, our study provides a platform that is suitable for real‐time visualization of various entry inhibitors, neutralizing antibodies, and sEV‐based decoy in blocking viral entry.Teaser: Comprehensive observation of SARS‐CoV‐2 spike and its interaction with receptor ACE2 and sEV‐based decoy in real time using HS‐AFM.

Adipose tissue (AT) macrophages (ATMs) are key players for regulation of AT homeostasis and obesity-related metabolic disorders. However, the phenotypes of human ATMs and regulatory mechanisms of their polarization have not been clearly described. In this study, we investigated human ATMs in both abdominal visceral AT and s.c. AT and proposed an 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1)–glucocorticoid receptor regulatory axis that might dictate M1/M2 polarization in ATMs. The accumulation of CD11c⁺CD163⁺ ATMs in both visceral AT and s.c. AT of obese individuals was confirmed at the cellular level and was found to be clearly correlated with body mass index and production of reactive oxygen species. Using our in vitro system where human peripheral blood monocytes (hPBMs) were cocultured with Simpson–Golabi–Behmel syndrome adipocytes, M1/M2 polarization was found to be dependent on 11β-HSD1, an intracellular glucocorticoid reactivating enzyme. Exposure of hPBMs to cortisol-induced expression of CD163 and RU-486, a glucocorticoid receptor antagonist, significantly abrogated CD163 expression through coculture of mature adipocytes with hPBMs. Moreover, 11β-HSD1 was expressed in crown ATMs in obese AT. Importantly, conditioned medium from coculture of adipocytes with hPBMs enhanced proliferation of human breast cancer MCF7 and MDA-MB-231 cells. In summary, the phenotypic switch of ATMs from M2 to mixed M1/M2 phenotype occurred through differentiation of adipocytes in obese individuals, and upregulation of intracellular 11β-HSD1 might play a role in the process.

The host nucleocytoplasmic trafficking system is often hijacked by viruses to accomplish their replication and to suppress the host immune response. Viruses encode many factors that interact with the host nuclear transport receptors (NTRs) and the nucleoporins of the nuclear pore complex (NPC) to access the host nucleus. In this review, we discuss the viral factors and the host factors involved in the nuclear import and export of viral components. As nucleocytoplasmic shuttling is vital for the replication of many viruses, we also review several drugs that target the host nuclear transport machinery and discuss their feasibility for use in antiviral treatment.

The emergence of large-scale order in self-organized systems relies on local interactions between individual components. During bacterial cell division, FtsZ—a prokaryotic homologue of the eukaryotic protein tubulin—polymerizes into treadmilling filaments that further organize into a cytoskeletal ring. In vitro, FtsZ filaments can form dynamic chiral assemblies. However, how the active and passive properties of individual filaments relate to these large-scale self-organized structures remains poorly understood. Here we connect single-filament properties with the mesoscopic scale by combining minimal active matter simulations and biochemical reconstitution experiments. We show that the density and flexibility of active chiral filaments define their global order. At intermediate densities, curved, flexible filaments organize into chiral rings and polar bands. An effectively nematic organization dominates for high densities and for straight, mutant filaments with increased rigidity. Our predicted phase diagram quantitatively captures these features, demonstrating how the flexibility, density and chirality of the active filaments affect their collective behaviour. Our findings shed light on the fundamental properties of active chiral matter and explain how treadmilling FtsZ filaments organize during bacterial cell division.

Small extracellular vesicles (sEVs) play a crucial role in local and distant cell communication. The intrinsic properties of sEVs make them compatible biomaterials for drug delivery, vaccines, and theranostic nanoparticles. Although sEV proteomics have been robustly studied, a direct instantaneous assessment of sEV structure dynamics remains difficult. Here, we use the high‐speed atomic force microscopy (HS‐AFM) to evaluate nanotopological changes of sEVs with respect to different physicochemical stresses including thermal stress, pH, and osmotic stress. The sEV structure is severely altered at high‐temperature, high‐pH, or hypertonic conditions. Surprisingly, the spherical shape of the sEVs is maintained in acidic or hypotonic environments. Real‐time observation by HS‐AFM imaging reveals an irreversible structural change in the sEVs during transition of pH or osmolarity. HS‐AFM imaging provides both qualitative and quantitative data at high spatiotemporal resolution (nanoscopic and millisecond levels). In summary, our study demonstrates the feasibility of HS‐AFM for structural characterization and assessment of nanoparticles.