[Preparation and penetrating effect of the polyarginine-enhanced green fluorescence protein fusion protein].

The aim of the study is to establish a platform to deliver therapeutic proteins into target cells through a polyarginine-based cell penetrating peptide. To facilitate the expression of therapeutic proteins, a pSUMO (Small Ubiquitin-like Modifier)-R9-EGFP (enhanced green fluorescence protein) prokaryotic expression vector was constructed. After induction, the fusion protein SUMO-R9-EGFP was efficiently expressed. To validate the cell penetrating ability of the fusion protein, HepG2 cells were incubated with the purified R9-EGFP or EGFP protein as control, internalization of the fluorescent proteins was examined by either flow cytometry or confocal microscopy. The result obtained by flow cytometry showed that the R9-EGFP fusion protein could efficiently penetrate into the HepG2 cells in a dose and time-dependent manner. In contrast, the fluorescence was barely detected in the HepG2 cells incubated with EGFP control. The fluorescence intensity of the R9-EGFP treated cells reached plateau phase after 1.5 h. The result obtained by confocal microscopy shows that R9-EGFP efficiently entered into the HepG2 cells and was exclusively located in the cytoplasm, whereas, no fluorescence was detected in the cells incubated with the EGFP control. The heparin inhibition experiment showed that heparin could inhibit penetrating effect of the R9-EGFP protein by about 50%, suggesting that the penetrating ability of the fusion protein is heparin-dependent. In summary, the study has established a platform to deliver therapeutic proteins into target cells through a polyarginine-based penetrating peptide.