Visualization of the COPII vesicle formation process reconstituted on a microscope

Transport from the endoplasmic reticulum to the Golgi body is ensured by a protein complex called COPII. Because the COPII vesicles are covered by the COPII coat protein - which consists of the low molecular weight GTPase Sar1p, Sec23/24p, and Sec13/31p, the transported proteins are selectively incorporated into the COPII vesicles by binding directly to the COPII coat. In this study, we reconstituted the formation of COPII vesicles on artificial planar lipid bilayer membranes, and visualized the dynamics of fluorescent-labeled transported proteins at a single molecular level, using a Total Internal Reflection Fluorescence Microscope (TIRFM). Then, the clusters of cargo molecules were observed by addition of Sec13/31p, revealing that the cargo molecules were concentrated inside the clusters. In addition, it has been revealed that the non-cargo molecules were excluded from the clusters. In this communication, we discuss the dynamics of cargo molecule in the process of COPII vesicle formation.