Membrane geometry and interactions between proteins

Based on a detailed study of the bacterial Shiga toxin we discuss the membrane mediated interactions between membrane inclusions. Shiga toxin interacts with its cellular receptor, the glycosphingolipid globotriaosylceramide (Gb3 or CD77), as a first step to entering target cells. This is followed by clustering of the Shiga Toxin-receptor complexes at the membrane and tubular invagination into the cytoplasm of the cell. Since neither direct forces between Shiga Toxins, lipid or solvent depletion forces or capillary forces can explain the clustering, we venture into the studies of the more subtle membrane mediated forces: curvature forces and thermal Casimir forces. Through a combination of theoretical analysis, computer simulations and experiments we conclude that thermal Casimir forces can be  major players in the lateral and morphological organization of the membrane.