Living cells segregate molecules and reactions in various subcellular compartments known as organelles. Spatial organization is likely essential for expanding the biochemical functions of synthetic reaction systems, including artificial cells. Many studies have attempted to mimic organelle functions using lamellar membrane-bound vesicles. However, vesicles typically suffer from highly limited transport across the membranes and an inability to mimic the dense membrane networks typically found in organelles such as the endoplasmic reticulum. Here, we describe programmable synthetic organelles based on highly stable nonlamellar sponge phase droplets that spontaneously assemble from a single-chain galactolipid and nonionic detergents. Due to their nanoporous structure, lipid sponge droplets readily exchange materials with the surrounding environment. In addition, the sponge phase contains a dense network of lipid bilayers and nanometric aqueous channels, which allows different classes of molecules to partition based on their size, polarity, and specific binding motifs. The sequestration of biologically relevant macromolecules can be programmed by the addition of suitably functionalized amphiphiles to the droplets. We demonstrate that droplets can harbor functional soluble and transmembrane proteins, allowing for the colocalization and concentration of enzymes and substrates to enhance reaction rates. Droplets protect bound proteins from proteases, and these interactions can be engineered to be reversible and optically controlled. Our results show that lipid sponge droplets permit the facile integration of membrane-rich environments and self-assembling spatial organization with biochemical reaction systems.
Amphiphilic
molecules undergo self-assembly in aqueous medium to
yield various supramolecular structures depending on their chemical
structure and molecular geometry. Among these, lamellar membrane-bound
vesicles are of special interest due to their resemblance to cellular
membranes. Here we describe the self-assembly of single-chain amide-linked
amphiphiles derived from β-d-galactopyranosylamine
and various unsaturated fatty acids into vesicles. In contrast, the
analogous amphiphiles derived from β-d-glucopyranosylamine
self-assemble into nanotubes. Fluorescence spectroscopy, X-ray diffraction,
and differential scanning calorimetry are used to determine various
physical parameters pertinent to the self-assembly process. The vesicular
architecture is characterized using optical microscopy and transmission
electron microscopy. Moreover, we show that the vesicles derived from
these amphiphiles can encapsulate molecules of various sizes and host
model biochemical reactions. Our work demonstrates that single-chain
glycolipid-based amphiphiles could serve as robust building blocks
for artificial cells and have potential applications in drug delivery
and microreactor design.
Single-chain
amphiphiles (SCAs) that self-assemble into large vesicular
structures are attractive components of synthetic cells because of
the simplicity of bilayer formation and increased membrane permeability.
However, SCAs commonly used for vesicle formation suffer from restricted
working pH ranges, instability to divalent cations, and the inhibition
of biocatalysts. Construction of more robust biocompatible membranes
from SCAs would have significant benefits. We describe the formation
of highly stable vesicles from alkyl galactopyranose thioesters. The
compatibility of these uncharged SCAs with biomolecules makes possible
the encapsulation of functional enzymes and nucleic acids during the
vesicle generation process, enabling membrane protein reconstitution
and compartmentalized nucleic acid amplification, even when charged
precursors are supplied externally.
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