Cells bend their plasma membranes into highly curved forms to interact with the local environment, but how shape generation is regulated is not fully resolved. Here, we report a synergy between shape-generating processes in the cell interior and the external organization and composition of the cell-surface glycocalyx. Mucin biopolymers and long-chain polysaccharides within the glycocalyx can generate entropic forces that favor or disfavor the projection of spherical and finger-like extensions from the cell surface. A polymer brush model of the glycocalyx successfully predicts the effects of polymer size and cell-surface density on membrane morphologies. Specific glycocalyx compositions can also induce plasma membrane instabilities to generate more exotic undulating and pearled membrane structures and drive secretion of extracellular vesicles. Together, our results suggest a fundamental role for the glycocalyx in regulating curved membrane features that serve in communication between cells and with the extracellular matrix. (A) The native and synthetic mucin biopolymers that were genetically encoded and used throughout this work. (B) Quantification of membrane tube density in epithelial cells. Mucin polymers induce dramatic tubularization compared to wild-type (Control) cells and compared to a similarly sized biopolymer composed of EGF-like repeats from Notch1 and the Muc1 transmembrane anchor with GFP reporter (EGF-repeats GFP-DCT) cells. Number of cells analyzed is shown on the x axis for each condition. Box notches here and elsewhere indicate 95% confidence intervals. The number of tandem repeats (TRs) are indicated in Muc1 constructs. (C) Scanning electron microscopy (SEM) images of cells expressing the indicated biopolymer. (D) Labelled glycans and membrane morphologies resolved with single-molecule localization microscopy in Muc1-42TR DCT-expressing cells before and after mucin backbone digestion with the StcE mucinase. Images are shown as 2D color-coded histograms of localizations with 32 nm bin width. (E) Representative confocal images of GUVs with and without anchorage of recombinant Podocalyxin. (F) (Left) Cartoons of Muc1 GFP-DCT polymers of varying length. (Right) Flow cytometry data showing similar cell-surface expression levels of the mucins using a GFP-binding nanobody, n = 3, >40,000 cells per population. (G) Representative SEM images of cells expressing mucins with a varying number of TRs. (H) Quantification of membrane tube density for cells expressing the indicated mucins, significance compared to 42TR. ***p < 0.001; ns, not significant (post-hoc Student's two-tailed t test). See also Figure S1.

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The size of whole Rhodobacter sphaeroides prevents 3D visualization of centermost chromatophores in their native environment. This study combines cryo-focused ion beam milling with cryo-electron tomography to probe vesicle architecture both in situ and in 3D. Developing chromatophores are membrane-bound buds that remain in topological continuity with the cytoplasmic membrane and detach into vesicles when mature. Mature chromatophores closest to the cell wall are typically isolated vesicles, whereas centermost chromatophores are either linked to neighboring chromatophores or contain smaller, budding structures. Isolated chromatophores comprised a minority of centermost chromatophores. Connections between vesicles in growing bacteria are through ~10 nm-long, ~5 nm-wide linkers, and are thus physical rather than functional in terms of converting photons to ATP. In cells in the stationary phase, chromatophores fuse with neighboring vesicles, lose their spherical structure, and greatly increase in volume. The fusion and morphological changes seen in older bacteria are likely a consequence of the aging process, and are not representative of connectivity in healthy R. sphaeroides. Our results suggest that chromatophores can adopt either isolated or connected morphologies within a single bacterium. Revealing the organization of chromatophore vesicles throughout the cell is an important step in understanding the photosynthetic mechanisms in R. sphaeroides.

Abstract:Building on the application of cuprite (Cu 2 O) in solar energy technologies and reports of increased optical absorption caused by metal-to-semiconductor energy transfer, a confinement-based strategy was developed to fabricate high aspect ratio, crystalline Cu 2 O nanorods containing entrapped gold nanoparticles (Au nps). Cu 2 O was crystallized within the confines of track-etch membrane pores, where this physical, assembly-based method eliminates the necessity of specific chemical interactions to achieve a well-defined metalsemiconductor interface. With high-resolution scanning/transmission electron microscopy (S/TEM) and tomography, we demonstrate the encasement of the majority of Au nps by crystalline Cu 2 O and show that crystalline Au-Cu 2 O interfaces that are free of extended amorphous regions. Such nanocrystal heterostructures are good candidates for studying the transport physics of metal/semiconductor hybrids for optoelectronic applications.

Experimental studies that follow behavior of single probes embedded in heterogeneous systems are increasingly common. The presence of probes may perturb the system, and such perturbations may or may not affect interpretation of host behavior from the probe observables typically measured. In this study, the manifestations of potential probe-induced changes to host dynamics in supercooled liquids are investigated via molecular dynamics simulations. It is found that probe dynamics do not necessarily mirror host dynamics as they exist either in the probe-free or probe-bearing systems. In particular, for a binary supercooled liquid, we find that smooth probes larger than the host particles induce increased translational diffusion in the host system; however, the diffusion is anisotropic and enhances caging of the probe, suppressing probe translational diffusion. This in turn may lead experiments that follow probe diffusion to suggest Stokes-Einstein behavior of the system even while both the probe-free and probe-bearing systems exhibit deviations from that behavior.