Deformation of Vesicles Controlled by Local Spontaneous Curvatures of Membrane

Abstract

The metabolic pathways are fundamental processes to maintain the life, which is supported by the cell membrane deformations such as, membrane adhesion, fusion and pore formation. In the present living organisms, the membrane deformations in the metabolic pathways are conducted by the related proteins. However, we believe that such membrane deformations can be caused by controlling the physical properties of the membrane without the aid of proteins. In this context we demonstrate the deformations of vesicle by controlling the spontaneous curvature of lipids.First, we focused on the lipids with negative spontaneous curvature (NL: DPPE and DPhPC). The binary vesicles composed of NL and lipids with zero spontaneous curvature (ZL: DOPC and DPPC) show a phase separation between NL rich domains and ZL rich matrix under the immiscibility temperature. When the two phase separating vesicles are contacted using micropipettes, they adhere each other through the domain rich in NL.Second, we have investigated the effects of the lipids with positive spontaneous curvature (PL: DHPC) on the shape of vesicles. The binary vesicles composed of PL and ZL form spherical shape in one-phase region. By decreasing the temperature, the binary vesicles show a burst and then form a single pore on the vesicle. There are three types of pores, simple circular, rolled-rim and wrinkle-rim, depending on the ratio of PL to ZL. The pore closes with increase the temperature and finally vesicles return to the spherical shape again. We discuss this shape deformation of vesicles by calculating time development equation of the membrane free energy.We believe that the control of the spontaneous curvature of lipids is a key to realize the model metabolic pathways without proteins.