Construction of Artificial Cell as an Autonomous Supramolecular Machine

A living cell can be regarded as an ideal machine. To understand the origin of life, it is important to construct a model protocell from a chemical aspect. We have developed a model protocell based on a giant vesicle (GV) in which the self-reproduction of GVs and the replication of their internal DNA proceed in tandem. The success of this linked self-reproduction was attributed to the spontaneous formation of a supramolecular catalyst (C@DNA) consisting of DNA and a protic amphiphile (C), both of which are embedded in the membrane. This model protocell can be viewed as a proliferating supramolecular machine. Furthermore, the frequency and pattern of GV division were found to depend not on the base sequence but on the length of the encapsulated DNA. The C@DNA functions as a lipo-deoxyribosome, and there is a causal relationship between the length of the DNA comprising C@DNA and frequency of protocell proliferation. On the other hand, the newly constructed recursive loop of proliferation consists of four stages: ingestion, replication, maturation, and division, with similarities to the four stages of the living cell cycle. The GV-based model protocells responsible for this soft information flow are sensitive to the environment (starvation time) and exhibit phenotypic plasticity. It was found that a dominant species emerged in an intense competitive proliferation among GVs with DNA of different lengths. This primitive natural selection is a step toward the ultimate goal of model protocells: supramolecular machines that can mimic evolution.