Reconstruction of Average Subtracted Tubular Regions (RASTR) enables structure determination of tubular filaments by cryo-EM.

As the field of electron microscopy advances, the increasing complexity of samples being produced demand more involved processing methods. In this study, we have developed a new processing method for generating 3D reconstructions of tubular structures. Tubular biomolecules are common throughout many cellular processes and are appealing targets for biophysical research. Processing of tubules with helical symmetry is relatively straightforward for electron microscopy if the helical parameters are known, but tubular structures that deviate from helical symmetry (asymmetrical components, local but no global order, etc) present myriad issues. Here we present a new processing technique called Reconstruction of Average Subtracted Tubular Regions (RASTR), which was developed to reconstruct tubular structures without applying symmetry. We explain the RASTR approach and quantify its performance using three examples: a simulated symmetrical tubular filament, a symmetrical tubular filament from cryo-EM data, and a membrane tubule coated with locally ordered but not globally ordered proteins.

Lipid domain formation and membrane shaping by C24-ceramide.

Ceramides are an important group of sphingolipids that modulate several cellular events. The mechanisms underlying biological actions of ceramides are not fully known, but evidence suggests that ceramides can act through regulation of the biophysical properties of the membrane. However, ceramide-induced changes on membrane properties are complex and depend on several factors. To gain further insight into this subject, we characterized the biophysical impact of very-long acyl chain C24-ceramide in a fluid model membrane under thermodynamic equilibrium and non-equilibrium conditions. Our results show that C24-ceramide readily forms two types of gel domains with distinct properties, likely corresponding to different interdigitated metastable gel phases. Upon reaching thermodynamic equilibrium, only partially interdigitated gel phase coexists with the fluid phase. In addition, C24-ceramide promotes strong changes in the shape of the vesicles, including domains with sharp edges and tubule-like structures. The results suggest that the formation of very long acyl chain ceramides in response to stress stimuli will initially induce a multitude of changes in the organization and fluidity of biological membranes that might be responsible for the activation of different cellular processes.

PLA2-Triggered Release of Drugs from Self-Assembled Lipid Tubules for Arthritis Treatments.

Environment-responsive drug delivery is a promising approach for tailoring the drug release in drug therapy. In this study, we develop lipid tubules by the self-assembly of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (DC8,9PC). These lipid tubules are capable of encapsulating hydrophobic dexamethasone (Dex) and hydrophilic dexamethasone sodium phosphate (DSP) simultaneously. In vitro studies show that the lipid tubules can be internalized by cells with no significant toxicity. We find that phospholipase (PLA2) is able to slowly digest the lipid tubules and trigger the sustained release of Dex and DSP. After being subcutaneously administrated to the inflammatory sites of arthritic rats, we show that a single dose of drug-loaded lipid tubules can remarkably inhibit the degree of joint swelling at the inflammatory sites and suppress the content of proinflammatory cytokines in inflamed tissues for a long time by this sustained release of both Dex and DSP triggered by the highly expressed PLA2 at the inflamed sites. Our results highlight the potential of using PLA2-responsive lipid tubules as on-demand carriers for treating inflammatory diseases.

One-pot green synthesis of bimetallic hollow palladium-platinum nanotubes for enhanced catalytic reduction of p-nitrophenol.

Bimetallic alloy nanostructures have garnered much attention due to their unique performances in catalytic processes. However, decline in catalytic activity over the life span has been a protracted limitation, ascribed largely to the aggregation or dissociation of particles and still remains a challenge for manufacturing bimetallic nanostructures of sufficient stability. Herein, a surfactant- and solvent-free greener strategy is presented for the fabrication of bimetallic palladium-platinum (PdPt) nanotubes (NTs), deploying lipid tubules as template and ascorbic acid as a reducing agent; the ensuing NTs comprise crystalline tubal nanostructures of ∼12 µm length, ∼500 nm cross-sectional diameter, and ∼57 nm tube wall thickness. When used for the catalytic reduction of p-nitrophenol (PNP), the PdPt NTs delivered improved kinetic apparent rate constants (kapp) compared to Pt NTs (0.5 min-1vs. 0.2 min-1). Moreover, the NTs demonstrated high stability when used over multiple catalytic cycles thus opening up new potential routes for the fabrication of alloy NTs using lipid tubules as templates.

Nonlocal strain gradient beam model for postbuckling and associated vibrational response of lipid supramolecular protein micro/nano-tubules.

As a supramolecular construction, lipid protein micro/nano-tubules can be utilized in a variety of sustained biological delivery system. The high slenderness ratio of lipid tubules makes their hierarchical assembly into a desired architecture difficult. Therefore, an accurate prediction of mechanical behavior of lipid tubular is essential. The objective of this study is to capture size dependency in the postbuckling and vibrational response of the postbuckled lipid micro/nano-tubules more comprehensively. To this purpose, the nonlocal strain gradient elasticity theory is incorporated to the third-order shear deformation beam theory to develop an unconventional beam model. Hamilton's principle is put to use to establish the size-dependent governing differential equations of motion. After that, an improved perturbation technique in conjunction with Galerkin method is employed to obtain the nonlocal strain gradient load-frequency response and postbuckling stability curves of lipid micro/nano-tubules. It is revealed that by taking the nonlocal size effect into consideration, the influence of the type (geometrical parameters) of an axially compressed lipid micro/nano-tubule on its natural frequency in order decreases and increases within the prebuckling and postbuckling regimes. While the strain gradient size dependency plays an opposite role which causes that the influence of the type of lipid micro/nano-tubule on its natural frequency corresponding to the prebuckling and postbuckling domains increases and decreases, respectively.

Lipid tubule growth by osmotic pressure.

We present here a procedure for growing lipid tubules in vitro. This method allows us to grow tubules of consistent shape and structure, and thus can be a useful tool for nano-engineering applications. There are three stages during the tubule growth process: initiation, elongation and termination. Balancing the forces that act on the tubule head shows that the growth of tubules during the elongation phase depends on the balance between osmotic pressure and the viscous drag exerted on the membrane from the substrate and the external fluid. Using a combination of mathematical modelling and experiment, we identify the key forces that control tubule growth during the elongation phase.