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Beating Vesicles: Encapsulated Protein Oscillations Cause Dynamic Membrane Deformations.

ABSTRACT: The bacterial Min protein system was encapsulated in giant unilamellar vesicles (GUVs). Using confocal fluorescence microscopy, we identified several distinct modes of spatiotemporal patterns inside spherical GUVs. For osmotically deflated GUVs, the vesicle shape actively changed in concert with the Min oscillations. The periodic relocation of Min proteins from the vesicle lumen to the membrane and back is accompanied by drastic changes in the mechanical properties of the lipid bilayer. In particular, two types of oscillating membrane-shape changes are highlighted: 1) GUVs that repeatedly undergo fission into two connected compartments and fusion of these compartments back into a dumbbell shape and 2) GUVs that show periodic budding and subsequent merging of the buds with the mother vesicle, accompanied by an overall shape change of the vesicle reminiscent of a bouncing ball. These findings demonstrate how reaction-diffusion-based protein self-organization can directly yield visible mechanical effects on membrane compartments, even up to autonomous division, without the need for coupling to cytoskeletal elements.

SUBMITTER: Litschel T

PROVIDER: S-EPMC6391971 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Dynamic covalent chemistry is exploited to drive morphological order-order transitions to achieve the controlled release of a model payload (e.g., silica nanoparticles) encapsulated within block copolymer vesicles. More specifically, poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer vesicles were prepared via aqueous polymerization-induced self-assembly in either the presence or absence of silica nanoparticles. Addition of 3-aminophenylboronic acid (APBA) to such vesicles results in specific binding of this reagent to some of the pendent cis-diol groups on the hydrophilic PGMA chains to form phenylboronate ester bonds in mildly alkaline aqueous solution (pH ∼ 10). This leads to a subtle increase in the effective volume fraction of this stabilizer block, which in turn causes a reduction in the packing parameter and hence induces a vesicle-to-worm (or vesicle-to-sphere) morphological transition. The evolution in copolymer morphology (and the associated sol-gel transitions) was monitored using dynamic light scattering, transmission electron microscopy, oscillatory rheology, and small-angle X-ray scattering. In contrast to the literature, in situ release of encapsulated silica nanoparticles is achieved via vesicle dissociation at room temperature; moreover, the rate of release can be fine-tuned by varying the solution pH and/or the APBA concentration. Furthermore, this strategy also works (i) for relatively thick-walled vesicles that do not normally exhibit stimulus-responsive behavior and (ii) in the presence of added salt. This novel molecular recognition strategy to trigger morphological transitions via dynamic covalent chemistry offers considerable scope for the design of new stimulus-responsive copolymer vesicles (and hydrogels) for targeted delivery and controlled release of cargoes. In particular, the conditions used in this new approach are relevant to liquid laundry formulations, whereby enzymes require protection to prevent their deactivation by bleach.

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Beating Vesicles: Encapsulated Protein Oscillations Cause Dynamic Membrane Deformations.

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