Charged liposome affects the translation and folding steps of in vitro expression of green fluorescent protein

The role of the charged liposome on the in vitro expression of green fluorescent protein (GFP) was investigated, focusing on its elemental steps such as transcription, translation and folding. The total GFP expression was enhanced to 145% when a neutral liposome (POPC: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocoline) was added externally to a cell-free translation system. On the contrary, the addition of the charged liposome composed of POPC with anionic 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (POPG) or cationic stearyl amine (SA) inhibited the total GFP expression, depending on the surface charge density of liposome. In transcription, the RNA synthesis was enhanced regardless of the variation of the surface charge, indicating that transcription was enhanced due to the stabilization of RNA structure by its hydrophobic interaction with liposome. Translation was inhibited by cationic liposome although it was enhanced by anionic liposome and neutral liposome. On the other hand, the folding was not inhibited in the presence of neutral liposome, whereas anionic liposome and cationic liposome inhibited the folding in proportion to the their surface charges, suggesting that the total GFP expression was controlled by a charged liposome in the translation step and folding step.