Emerging Advances of Cell‐Free Systems toward Artificial Cells

Abstract

models have attracted considerable attentions in order to unravel the inherent complexity. Although engineering modern cells has achieved some progress, [2] the arbitrary elimination of genomic information could probably remove some distinguished characteristics (top-down strategy). Building chemical systems that resemble the structure and behaviors of living cells by stepwise integration of pivotal components is also conceivable (bottom-up strategy). [3] These synthetic systems with biomimetic cellularity provide conceptual pathway from inanimate matter to artificial life, which are often known as artificial cells. [4] Due to the lack of full comprehension about the molecular mechanism of living cells, laborious reconstitution of complicated networks would be difficult and the disparities of protein behaviors in the artificial cells have been observed. Herein, we prefer to construct artificial cells by preserving certain endogenous machinery already existing in living cells. Such principle is conducible for maintaining essential features of living cells while leaving design space for synthetic biologists to study specific cellular behavior in bottom-up manner. [5] Cell-free system, also referred to as in vitro transcription and translation system is a universal toolbox to study the organisms of cell biology. [6] Cell-free extracts inherit most of the endogenous machinery including functional macromolecules as well as metabolic networks and the addition of desired resources could initiate coupled protein expressions. Indeed, the first appearance of cell-free systems could date back to 1961 when Nirenberg and Matthaei deciphered the genetic codes. [7] Featured by the accessible utilization of molecular machinery, cellfree systems could circumvent the frangibility and membrane barrier of biological cells. The transformative development of protein synthesis using recombinant elements (PURE) system with well-defined components greatly enhances the systemic manipulation and controllability. [8] In principle, the quintessence behind cell-free system is the central dogma that reflects the flow of genetic information, from plasmid DNA to messenger RNA (mRNA), to eventually make functional proteins. As such, artificial cells encapsulated with cell-free system could serve as the valuable candidate to construct numerous biological processes. [9] The powerful ability of protein expressions, which is deprived in other synthetic systems, offers advantageous scenario for enzymatic processes that are also guided by flexible and programmable regulations of gene circuit. [10] The execution of larger genetic programs could further permit the construction of complex biochemical systems. [11] More importantly, Artificial cells that mimic the architectural and functional characteristics of living cells not only shed light on the physical principle of life but also facilitate development in the areas such as cell engineering and biomedicine. Cell-free systems carry out the central dogma that refers to the transcription and translation ...

Phospholipid synthesis inside phospholipid membrane vesicles

“…The construction of artificial cells based on cell-free systems may lead to the development of new biological tools that will be a platform for the study of cellular biological processes or a fundamental technology for biomedicine 34 , 35 . One of the bottlenecks that impede the development of artificial cells is the delay in reproducing the self-reproduction ability of cells.…”

Droplet-Templated Synthetic Cells

“…In particular, the droplets serve as soft templates for the assembly of supramolecular vesicles or colloidosomes with unprecedented control in comparison with the bulk emulsification and mixing approaches. 9,26,68,69 This can be achieved either by using a single emulsion system composed of immiscible water and oil phases with the aid of solvent extraction (Figure 3A) 70 or via a double emulsion system together with a dewetting process (Figure 3B). 71 As the size of these assemblies is larger than those fabricated in the continuous-flow microfluidics, they are called giant vesicles.…”

Modularize and Unite: Toward Creating a Functional Artificial Cell

“…A significant difference between cells and solutions is the crowded environment inside the former. About 30% of the volume is occupied by macromolecules such as proteins, nucleic acids, and polysaccharides, whose concentration can reach 300-400 g/L (Zhu et al, 2020), and even 500 g/L in some compartments inside cells (Minton, 2015). The high concentration of macromolecules causes the so-called "macromolecular crowding" and brings significant effects to the interactions between participating biomolecules and the final metabolism (Rivas and Minton, 2016).…”

“…Millions of years of evolution have endowed living cells with a complex structure to overcome this difficulty. A natural eukaryotic cell has various organelles with different compositions and assumes different cellular functions ( Zhu et al, 2020 ). Even prokaryotic cells have nucleoids and ribosomes.…”