4′-Amino-benzamido-taurocholic Acid Selectively Solubilizes Glycosyl-phosphatidylinositol-Anchored Membrane Proteins and Improves Lipolytic Cleavage of Their Membrane Anchors by Specific Phospholipases

Glycosyl-phosphatidylinositol-anchored membrane proteins (GPI-proteins) are normally identified either by cleavage of the lipid anchor using (glycosyl)phosphatidylinositol-specific phospholipases C or D (GPI-PLs) or by metabolic labeling of the lipid moiety with specific building blocks. Therefore, methods for discrimination between transmembrane proteins and GPI-proteins on the basis of their physicochemical properties are desirable. Here we are presenting a selective extraction method for typical well-characterized mammalian GPI-proteins, e.g., acetylcholine esterase, alkaline phosphatase, 5′-nucleotidase, and lipoprotein lipase, using a derivative of taurocholate. The results were compared to those obtained with well-characterized transmembrane proteins, e.g., insulin receptor and hydroxymethyl glutaryl coenzyme A-reductase, glucose transporters, or aminopeptidase M and several commercially available detergents. With regard to total membrane proteins, it was possible to selectively enrich GPI-proteins up to 8- to 14-fold by using concentrations between 0.1 and 0.3% of 4′-NH2-amino-7β-benzamido-taurocholic acid (BATC). In addition, the cleavage specificity and efficiency of (G)PI-PLs were increased in the presence of identical concentrations of BATC compared to commonly used detergents, e.g., Nonidet P-40. Therefore, the present study shows that the use of BATC facilitates the identification of glycosyl-phosphatidylinositol-anchored membrane proteins.