Electrostatic regulation of liquid-liquid phase separation of DNA-polypeptide system

Liquid-liquid phase separation (LLPS) of proteins and nucleic acids play an important role in the formation of membraneless intracellular organelles and is related to some diseases due to abnormal protein aggregation.In the present study, we focus on the mechanism and regulation of LLPS of polylysine (PLL) and DNA solution.We found that the dominant interaction in PLL-DNA system is electronic force between them.Then we regulated its LLPS by adding ethanol and zwitterionic 6-Aminocaproic acid (6-A) which enhance and suppress electrostatic interaction between the macroions charged oppositely.The result showed when a fixed DNA concentration was kept in solution, LLPS occurred at a lower critical value of PLL concentration and disappeared at a higher critical concentration.The addition of ethanol shifted the range of LLPS upward, while 6-A shifted it downward.Specifically, for a fixed DNA concentration of 1 g/l, the critical PLL concentrations for LLPS were 0.4 g/l and 2 g/l, respectively.Upon addition of 20% ethanol, the critical PLL concentrations increased to 1 g/l and 4.5 g/l, respectively.On the other hand, the addition of 700 mM 6-A decreased the critical PLL concentrations to 0.35 g/l and 1 g/l, respectively.The results demonstrate that the adjustment of electrostatic interaction between DNA and counterions can effectively influence the LLPS of DNA.