Exploding vesicles

Peptide-Based Coacervate-Core Vesicles with Semipermeable Membranes

Coacervates droplets have long been considered as potential protocells to mimic living cells. However, these droplets lack a membrane and are prone to coalescence, limiting their ability to survive, interact, and organize into higher-order assemblies. This work shows that tyrosine-rich peptide conjugates can undergo liquid-liquid phase separation in a well-defined pH window and transform into stable membrane-enclosed protocells by enzymatic oxidation and cross-linking at the liquid-liquid interface. The oxidation of the tyrosine-rich peptides into dityrosine creates a semipermeable, flexible membrane around the coacervates with tunable thickness, which displays strong intrinsic fluorescence, and stabilizes the coacervate protocells against coalescence. The membranes have an effective molecular weight cut-off of 2.5 kDa, as determined from the partitioning of small dyes and labeled peptides, RNA, and polymers into the membrane-enclosed coacervate protocells. Flicker spectroscopy reveals a membrane bending rigidity of only 0.1k_B T, which is substantially lower than phospholipid bilayers despite a larger membrane thickness. Finally, it is shown that enzymes can be stably encapsulated inside the protocells and be supplied with substrates from outside, which opens the way for these membrane-bound compartments to be used as molecularly crowded artificial cells capable of communication or as a vehicle for drug delivery.

HIV-1 Vpr protein impairs lysosome clearance causing SNCA/alpha-synuclein accumulation in neurons

Despite the promising therapeutic effects of combinatory antiretroviral therapy (cART), 20% to 30% of HIV/AIDS patients living with long term infection still exhibit related cognitive and motor disorders. Clinical studies in HIV-infected patients revealed evidence of basal ganglia dysfunction, tremors, fine motor movement deficits, gait, balance, and increased risk of falls. Among older HIV⁺ adults, the frequency of cases with SNCA/α-synuclein staining is higher than in older healthy persons and may predict an increased risk of developing a neurodegenerative disease. The accumulation of SNCA aggregates known as Lewy Bodies is widely described to be directly linked to motor dysfunction. These aggregates are naturally removed by Macroautophagy/autophagy, a cellular housekeeping mechanism, that can be disturbed by HIV-1. The molecular mechanisms involved in linking HIV-1 proteins and autophagy remain mostly unclear and necessitates further exploration. We showed that HIV-1 Vpr protein triggers the accumulation of SNCA in neurons after decreasing lysosomal acidification, deregulating lysosome positioning, and the expression levels of several proteins involved in lysosomal maturation. Viruses and retroviruses such as HIV-1 are known to manipulate autophagy in order to use it for their replication while blocking the degradative final step, which could destroy the virus itself. Our study highlights how the suppression of neuronal autophagy by HIV-1 Vpr is a mechanism leading to toxic protein aggregation and neurodegeneration.Abbreviations: BLOC1: Biogenesis of Lysosome-related Organelles Complex 1; CART: combinatory antiretroviral therapy; CVB: coxsackievirus; DAPI: 4',6-diamidino-2-phenylindole; DENV: dengue virus; GFP: green fluorescent protein; HCV: hepatitis C virus; HCMV: human cytomegalovirus; HIV: human immunodeficiency virus; Env: HIV-1 envelope glycoproteins; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; VSV: Indiana vesiculovirus; LTR: Long Terminal Repeat; LAMP1: lysosomal associated membrane protein 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MLBs: multilamellar bodies; RIPA: Radioimmunoprecipitation assay buffer; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; Tat: transactivator of TAR; TEM: transmission electron microscope; Vpr: Viral protein R.

Bursting and Reassembly of Giant Double Emulsion Drops Form Polymer Vesicles

Polymeric vesicles are excellent building blocks of synthetic compartmentalized systems such as protocells and artificial organelles. In such applications, the efficient encapsulation of materials into the vesicles is an essential requirement. However, common encapsulation techniques can be time-consuming, demand special equipment or have limited efficiency for large components, such as proteins and nanoparticles. Here, we describe a simple method to create cargo-filled polymer vesicles based on bursting and reassembly of giant double emulsion droplets (DED). Due to their large average diameter of 2 mm, DEDs eventually burst in the aqueous medium, producing polymeric film fragments. These fragments rapidly reassemble into smaller vesicles in a process involving folding, fusion and vesiculation. The daughter vesicles have an average diameter of 10 μm, representing a two-order of magnitude size reduction compared to the original DED, and can efficiently encapsulate components present in solution by entrapment of the aqueous medium during vesicle reassembly.

Light-triggered explosion of lipid vesicles

Lipid vesicles have received considerable interest because of their applications to in vitro reductionist cell membrane models as well as therapeutic delivery vehicles. In these contexts, the mechanical response of vesicles in nonequilibrium environments plays a key role in determining the corresponding dynamics. A common understanding of the response of lipid vesicles upon exposure to a hypotonic solution is a characteristic pulsatile behavior. Recent experiments, however, have shown vesicles exploding under an osmotic shock generated by photo-reactions, yet the explanatory mechanism is unknown. Here we present a generalized biophysical model incorporating a stochastic account of membrane rupture to describe both swell-burst-reseal cycling and exploding dynamics. This model agrees well with experimental observations, and it unravels that the sudden osmotic shock strains the vesicle at an extreme rate, driving the vesicle into buckling instabilities responsible for membrane fragmentation, i.e. explosion. Our work not only advances the fundamental framework for non-equilibrium vesicle dynamics under osmotic stress, but also offers design guidelines for programmable vesicle-encapsulated substance release in therapeutic carriers.

A minimal biochemical route towards de novo formation of synthetic phospholipid membranes

All living cells consist of membrane compartments, which are mainly composed of phospholipids. Phospholipid synthesis is catalyzed by membrane-bound enzymes, which themselves require pre-existing membranes for function. Thus, the principle of membrane continuity creates a paradox when considering how the first biochemical membrane-synthesis machinery arose and has hampered efforts to develop simplified pathways for membrane generation in synthetic cells. Here, we develop a high-yielding strategy for de novo formation and growth of phospholipid membranes by repurposing a soluble enzyme FadD10 to form fatty acyl adenylates that react with amine-functionalized lysolipids to form phospholipids. Continuous supply of fresh precursors needed for lipid synthesis enables the growth of vesicles encapsulating FadD10. Using a minimal transcription/translation system, phospholipid vesicles are generated de novo in the presence of DNA encoding FadD10. Our findings suggest that alternate chemistries can produce and maintain synthetic phospholipid membranes and provides a strategy for generating membrane-based materials.

The origin of phospholipids, the primary constituents of cell membranes, is uncertain. Here, the authors develop an in vitro system to synthesize phospholipid molecules from water-soluble single-chain amphiphilic precursors via a reaction catalysed by the mycobacterial ligase FadD10.

Chemomimesis and Molecular Darwinism in Action: From Abiotic Generation of Nucleobases to Nucleosides and RNA

Molecular Darwinian evolution is an intrinsic property of reacting pools of molecules resulting in the adaptation of the system to changing conditions. It has no a priori aim. From the point of view of the origin of life, Darwinian selection behavior, when spontaneously emerging in the ensembles of molecules composing prebiotic pools, initiates subsequent evolution of increasingly complex and innovative chemical information. On the conservation side, it is a posteriori observed that numerous biological processes are based on prebiotically promptly made compounds, as proposed by the concept of Chemomimesis. Molecular Darwinian evolution and Chemomimesis are principles acting in balanced cooperation in the frame of Systems Chemistry. The one-pot synthesis of nucleosides in radical chemistry conditions is possibly a telling example of the operation of these principles. Other indications of similar cases of molecular evolution can be found among biogenic processes.

Lysosome Enlargement Enhanced Photochemotherapy Using a Multifunctional Nanogel

Large lysosomes are susceptible toward rupture because of an increased membrane tension. Here we report a strategy to first enlarge and weaken the lysosome and then destroy it to boost the efficiency of photochemotherapy using a hyaluronan nanogel, carrying chloroquine as a lysosomal expander, rhodamine B as a photosensitive lysosomal destroyer, and cisplatin as a chemotherapeutic. This all-in-one nanogel provides a facile approach and new insight into improve the photochemotherapy, by making use of lysosome's size, as a risk factor in lysosomal destabilization.

A Cell-Mimicking Structure Converting Analog Volume Changes to Digital Colorimetric Output with Molecular Selectivity

We herein report a three-component cell-mimicking structure with a peroxidase-like iron oxide nanozyme as the nucleus, a molecularly imprinted hydrogel shell as cytoplasm, and a lipid bilayer membrane. The structure was characterized by cryo and negative stain TEM and also by a calcein leakage test. By introducing charged monomers, the gel shell can swell or shrink in response to salt concentration. By lowering the salt concentration, the gradual "analog" gel volume change was reflected in a switch-like "digital" colorimetric output by the burst of membrane and oxidation of substrates such as 3,3',5,5'-tetramethylbenzidine (TMB). Controlled access was also achieved by using melittin to insert channels cross the membrane, and selective molecular transport was realized by the molecularly imprinted gel. The functions of each component are coupled, and this sophisticated tripartite structure provides a new platform for modular design of new materials. Our cell-mimicking structure is functional and it is complementary to the current protocell work that aims to understand the origin of life.

Phosphorylation, oligomerization and self-assembly in water under potential prebiotic conditions

Prebiotic phosphorylation of (pre)biological substrates under aqueous conditions is a critical step in the origins of life. Previous investigations have had limited success and/or require unique environments that are incompatible with subsequent generation of the corresponding oligomers or higher-order structures. Here, we demonstrate that diamidophosphate (DAP)-a plausible prebiotic agent produced from trimetaphosphate-efficiently (amido)phosphorylates a wide variety of (pre)biological building blocks (nucleosides/tides, amino acids and lipid precursors) under aqueous (solution/paste) conditions, without the need for a condensing agent. Significantly, higher-order structures (oligonucleotides, peptides and liposomes) are formed under the same phosphorylation reaction conditions. This plausible prebiotic phosphorylation process under similar reaction conditions could enable the systems chemistry of the three classes of (pre)biologically relevant molecules and their oligomers, in a single-pot aqueous environment.

A Nonconventional Model of Protocell-like Vesicles: Anionic Clay Surface-Mediated Formation from a Single-Tailed Amphiphile

We report a novel model system of precursor cellular membranes, self-assembled from micellar solution of a common anionic single-tailed amphiphile (STA), including sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS). The self-assembly process was mediated with solid surfaces of Mg2Al-CO3 hydrotalcite-like compound (HTlc), an anionic clay, in the absence of cosurfactants or any additives. The resultant STA vesicles were characterized using negative-staining and cryogenic transmission electron microscopies, as well as dynamic light scattering and steady state fluorescence techniques. Interestingly, the obtained STA vesicles displayed good stability even after the removal of the anionic clay surface (ACS), and a self-reproduction phenomenon was observed for the "preformed" STA vesicles when mixing with corresponding STA micellar solutions. More importantly, the micelle-to-vesicle transition for SDS could be still arisen in high-salinity artificial seawater under the ACS mediation. Instead of conventional fatty acid scenario, our finding provides another novel possible model for protocell-like vesicles, which are easily formed under the plausible prebiotic conditions.

A cell-targeted photodynamic nanomedicine strategy for head and neck cancers

Photodynamic therapy (PDT) holds great promise for the treatment of head and neck (H&N) carcinomas where repeated loco-regional therapy often becomes necessary due to the highly aggressive and recurrent nature of the cancers. While interstitial light delivery technologies are being refined for PDT of H&N and other cancers, a parallel clinically relevant research area is the formulation of photosensitizers in nanovehicles that allow systemic administration yet preferential enhanced uptake in the tumor. This approach can render dual-selectivity of PDT, by harnessing both the drug and the light delivery within the tumor. To this end, we report on a cell-targeted nanomedicine approach for the photosensitizer silicon phthalocyanine-4 (Pc 4), by packaging it within polymeric micelles that are surface-decorated with GE11-peptides to promote enhanced cell-selective binding and receptor-mediated internalization in EGFR-overexpressing H&N cancer cells. Using fluorescence spectroscopy and confocal microscopy, we demonstrate in vitro that the EGFR-targeted Pc 4-nanoformulation undergoes faster and higher uptake in EGFR-overexpressing H&N SCC-15 cells. We further demonstrate that this enhanced Pc 4 uptake results in significant cell-killing and drastically reduced post-PDT clonogenicity. Building on this in vitro data, we demonstrate that the EGFR-targeted Pc 4-nanoformulation results in significant intratumoral drug uptake and subsequent enhanced PDT response, in vivo, in SCC-15 xenografts in mice. Altogether our results show significant promise toward a cell-targeted photodynamic nanomedicine for effective treatment of H&N carcinomas.

Photochemically driven redox chemistry induces protocell membrane pearling and division

Prior to the evolution of complex biochemical machinery, the growth and division of simple primitive cells (protocells) must have been driven by environmental factors. We have previously demonstrated two pathways for fatty acid vesicle growth in which initially spherical vesicles grow into long filamentous vesicles; division is then mediated by fluid shear forces. Here we describe a different pathway for division that is independent of external mechanical forces. We show that the illumination of filamentous fatty acid vesicles containing either a fluorescent dye in the encapsulated aqueous phase, or hydroxypyrene in the membrane, rapidly induces pearling and subsequent division in the presence of thiols. The mechanism of this photochemically driven pathway most likely involves the generation of reactive oxygen species, which oxidize thiols to disulfide-containing compounds that associate with fatty acid membranes, inducing a change in surface tension and causing pearling and subsequent division. This vesicle division pathway provides an alternative route for the emergence of early self-replicating cell-like structures, particularly in thiol-rich surface environments where UV-absorbing polycyclic aromatic hydrocarbons (PAHs) could have facilitated protocell division. The subsequent evolution of cellular metabolic processes controlling the thiol:disulfide redox state would have enabled autonomous cellular control of the timing of cell division, a major step in the origin of cellular life.