Fission and Internal Fusion of Protocell with Membraneless “Organelles” Formed by Liquid–Liquid Phase Separation

Abstract

Construction of protocells with hierarchical structures and living functions is still a great challenge. Growing evidence demonstrates that the membraneless organelles, which facilitate many essential cellular processes, are formed by RNA, protein, and other biopolymers via liquid–liquid phase separation (LLPS). The formation of the protocell in the early days of Earth could follow the same principle. In this work, we develop a novel coacervate-based protocell containing membraneless subcompartments via spontaneous liquid–liquid phase separation by simply mixing single-stranded oligonucleotides (ss-oligo), quaternized dextran (Q-dextran), and poly­(l-lysine) (PLL) together. The resulting biphasic droplet, with PLL/ss-oligo phase being the internal subcompartments and Q-dextran/ss-oligo phase as the surrounding medium, is capable of sequestering and partitioning biomolecules into distinct regions. When the droplet is exposed to salt or Dextranase, the surrounding Q-dextran/ss-oligo phase will be gradually dissociated, resulting in the chaotic movement and fusion of internal subcompartments. Besides, the external electric field at a lower strength can drive the biphasic droplet to undergo a deviated circulation concomitant with the fusion of localized subcompartments, while a high-strength electric field can polarize the whole droplet, resulting in the release of daughter droplets in a controllable manner. Our study highlights that liquid–liquid phase separation of biopolymers is a powerful strategy to construct hierarchically structured protocells resembling the morphology and functions of living cells and provides a step toward a better understanding of the transition mechanism from nonliving to living matter under prebiotic conditions.

Liquid–liquid crystalline phase separation in biological filamentous colloids: nucleation, growth and order–order transitions of cholesteric tactoids

“… 4 This phenomenon is called liquid–liquid phase separation (LLPS), 5 which can be achieved by changing the pressure, temperature or concentration. 6 Liquid–liquid phase separation in biology is associated with a multitude of cellular functions and structures, 7 such as in membrane-less organelles, 8 and understanding this process has important implications in the elucidation of several mechanisms of life functioning. The most common form of liquid–liquid phase separation involves two biopolymers ( e.g.…”

Protocells: Milestones and Recent Advances

“…[136] They are generated by a liquid-liquid phase separation process, and have found extensive use as a tunable dynamic model for artificial cells or organelles. [137][138][139][140][141] Particularly interesting are "active" Small 2022, 18, 2106624 The gas-water interface can provide two types of compartments: water particles suspended in air (aerosols), and gas bubbles suspended in water, which can accommodate biosurfactants at the interface. e) A frozen water-ice matrix upconcentrates solutes.…”

“…[ 136 ] They are generated by a liquid–liquid phase separation process, and have found extensive use as a tunable dynamic model for artificial cells or organelles. [ 137–141 ] Particularly interesting are “active” coacervates, governed by an incorporated organic reaction which supplies the droplet with de novo synthesized material for autonomous growth. [ 142 ] The possible role of coacervates in the origin of life has been recently repeatedly reviewed.…”

A material‐based panspermia hypothesis: The potential of polymer gels and membraneless droplets

“…[156] On the other hand, passive coalescence occurs when droplets move freely via Brownian motion, and when two droplets similar in size contact each other randomly, they then fuse into a single larger droplet. [157,158] Preliminary results show that NaCl concentration increases induce membraneless polyester droplet coalescence, potentially due to migration of ions to the droplet interface, resulting in surface tension or surface charge changes, [127,159] while temperature increases can also accelerate membraneless droplet coalescence. [160] The rate of coalescence depends on aqueous solution properties as well, such as phase volumes and viscosities.…”