5] Membrane proteins

Abstract

Publisher Summary Depending on the type of interaction, membrane proteins are either embedded into a lipid bilayer or associated with the membrane structures, in the latter case, usually by ionic interaction or by hydrogen bonds. To isolate and analyze these proteins, they must be extracted from the membrane structures— that is, solubilized. Solubilization is mostly carried out with detergents. In this chapter, to illustrate the strategy for high-resolution separation of membrane proteins, the chromatographic and electrophoretic separation of proteins from the plasma membranes of the liver and Morris hepatomas is shown. Three groups of proteins are chosen, with different degrees of hydrophobicity. Membrane-associated annexins [calcium-binding protein (CBP) 65/67, CBP 35, and CBP 33] are less hydrophobic and can be solubilized, without using detergents. These proteins can be phosphorylated, but they are not glycosylated. Dipeptidyl-peptidase IV (DPP IV; EC 3.4.14.5) and the cell-cell adhesion protein cell-CAM (cell adhesion molecule or gp110) are intrinsic membrane proteins, and they are also glycosylated. Other membrane proteins, e.g., from eukaryotic cells or of bacterial and viral origin, can be assigned to one of the above-mentioned groups, in accordance with their behavior in chromatographic as well as electrophoretic separations.