Peptide‐Based Coacervate‐Core Vesicles with Semipermeable Membranes

Abstract

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 0.1kBT, 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.

Peptide-based coacervates in therapeutic applications

“…Recently, tyrosine-rich short peptides were claimed to enable the formation of semipermeable coacervate protocells due to the oxidation of spacers in the YFsFY peptide ( Abbas et al, 2022 ) . Since the phenolic side group of tyrosine had a pK a of approximately 10.5, the self-assembled condensate was dissolved when the pH value increased.…”

“…(J) Transmission electron microscopy images of coacervates (left) and CCVs (right); scale bars: 5 and 1 μm, respectively. (K) Stability of CCVs in comparison with the coacervates without oxidizing agents ( Abbas et al, 2022 ). Copyright © 2022 John Wiley & Sons, Inc.…”

Growth, replication and division enable evolution of coacervate protocells

“…The inside of a coacervates can be slightly more hydrophobic than the dilute phase, depending on the composition, which makes it a preferred environment for hydrophobic solutes. Simple and complex coacervates can be formed from a wide array of molecule types, ranging from long polymers, like complex coacervates formed by polycations and polyanions, 21 but also small molecules, like simple coacervates formed by a short peptide conjugate bearing a minimal sticker-spacer-sticker motif, 20,36 and complex coacervates formed by metabolites and short oligopeptides. 37 For protocells, the coacervates composed of the smallest and simplest molecules possible are most interesting, but all types of coacervates can be relevant to understanding the general principles for growth, replication and division.…”

Membranized Coacervate Microdroplets: from Versatile Protocell Models to Cytomimetic Materials

“…14,15 Moreover, the dynamic assembly/disassembly and multiple-phase condensation of coacervate microdroplet systems provide unprecedented opportunities for the spatiotemporal control of microscale organization. 16 Although coacervate microdroplets prepared by polyelectrolyte complexation or single-component liquid−liquid phase separation 17,18 have been broadly investigated as molecularly crowded model protocells, the absence of an enclosing membrane is a potential drawback for cytomimetic modeling and the development of functional cell-like materials. 19 In particular, coacervate-based protocells are susceptible to fusion and sensitive to salt/pH-induced instability, which ultimately gives rise to coalescence into a bulk phase over several minutes or hours.…”