Towards self-assembled hybrid artificial cells: novel bottom-up approaches to functional synthetic membranes

Abstract

There has been increasing interest in utilizing bottom-up approaches to develop synthetic cells. A popular methodology is the integration of functionalized synthetic membranes with biological systems, producing "hybrid" artificial cells. This Concept article covers recent advances and the current state-of-the-art of such hybrid systems. Specifically, we describe minimal supramolecular constructs that faithfully mimic the structure and/or function of living cells, often by controlling the assembly of highly ordered membrane architectures with defined functionality. These studies give us a deeper understanding of the nature of living systems, bring new insights into the origin of cellular life, and provide novel synthetic chassis for advancing synthetic biology.

Keywords: artificial cell; drug delivery; polymersome; synthetic biology; vesicles.

Figure 1

Fatty acid-based vesicles as protocells. Fatty acid vesicles containing a dipeptide catalyst seryl-histidine (Ser-His), which catalyzes the formation of a second dipeptide, N-Acetyl-L-phenylalanine-leucinamide (AcPheLeuNH₂). The newly-formed hydrophopic dipeptide localizes to the vesicle membranes, imparting enhanced affinity for fatty acids, thus promoting vesicle growth.

Figure 2

De novo self-assembly of phospholipid membranes. a) Membrane assembly driven by a copper-catalyzed biomimetic reaction. Azide oil droplets (orange) interact with alkyne lysolipid micelles (blue) in aqueous solution to form an emulsion. Copper catalyst (green) addition triggers azide-alkyne coupling via bioorthogonal triazole formation, which occurs at the interface between insoluble azide oil droplets and the alkyne-containing aqueous solution. This azide-alkyne cycloaddition spontaneously drives de novo phospholipid vesicle formation. b) Spontaneous vesicle assembly induced by NCL-based phospholipid synthesis.

Figure 3

Snapshots from a coarse-grained-simulation of the self-assembly process for the amphiphilic peptide bis(h₅)-K-K₄, which leads to stable β-like assemblies to adopt a vesicular morphology [Adapted from reference 14].

Figure 4

Self-assembly of amphiphilic glycodendrimers into uniform unilamellar vesicles (glycodendrimersomes), which exhibit specific and potent bioactivity in binding biomedically relevant lectins.

Figure 5

Schematic representation of a shell-in-shell polyelectrolyte multilayer capsule obtained by LbL assembly. Laser induced inter-compartmentalized mixing results due to light absorption by gold nanoparticles embedded into the inner shell.

Figure 6

Multicompartmentalized catalytic synthetic cells. Initially, encapsulation of enzymes occurs in polystyrene-b-poly(3-(isocyano-lalanyl-amino-ethyl)-thiophene) (PS-b-PIAT) nanoreactors, followed by mixing of the artificial organelles, cytosolic enzymes, and reagents, and subsequent encapsulation of the mixture in polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) vesicles to create the functional synthetic cell, inside which enzymatic multicompartment catalysis occurs.

Figure 7

Multicompartmentalized vesicles feature pH-responsive transmembrane channels. Multivesicle assemblies comprised of acrylic acid (AAc) and distearin acrylate (DSA) were prepared using a two-stage double emulsion. Increasing pH allows AAc residues to ionize, opening hydrophilic transmembrane channels.