One-step direct reconstitution of biomembranes onto cationic organic polymer bead supports

In this study, we addressed the straightforward reconstitution of red blood cell (RBC) membranes on the surface of cationic organic polymer beads. The RBC membrane-bead complex was obtained by the incubation of white, unsealed rat RBC ghost membranes with a nonporous quaternary ammonium-type anion-exchange polymer bead with a 350-550 microm diameter. Confocal microscopic observations using a fluorescence membrane probe revealed that the RBC membranes were reconstituted on the outer surface of the bead without any remarkable structural gaps in the membrane. The absence of activity of two peripheral enzymes that latently reside on the cytoplasmic face of the RBC membranes demonstrated that the orientation of the RBC membranes immobilized on the beads was asymmetric as well as that in the native state. The RBC membrane-polymer bead complex was incubated with a primary antibody that is directed against the amino-terminal extracellular domain of the integral protein glycophorin A (GPA). The resulting complex was further incubated with a fluorescent secondary antibody and then subjected to confocal microscopic observations. Fluorescence resulting in the binding of the secondary antibody was found on the surface of the complex, which indicates that the amino-terminal extracellular domain of GPA is exposed to the surface of the complex. In addition, the anion uptake function of the most abundant integral protein anion-exchanger 1 (AE1) immobilized on the polymer beads was inhibited by pretreatment with its specific inhibitor 4,4'-diisothiocyano-2,2'-stilbene disulfonate, as is observed for the intact RBCs. Based on all these results, the RBC membranes were thought to be reconstituted on the ionic polymer beads by our one-pot procedure while maintaining the orientation and functions of the membrane proteins to some extent.