Although immense scientific interest has propelled the invention and refinement of various methods tackling the aforementioned obstacles, coverage of the membrane proteome remains far from being exhaustive. The low abundance of this class of proteins – only 2% of all cellular proteins belong to the plasma membrane ( 1) – further impedes their detection. Analysis of the membrane proteome is hampered by the heterogeneity and amphiphilic nature of these proteins. If proteomic profiling by mass spectrometry is desired, proteins are denatured, carbamidomethylated, and digested into peptides prior to chromatography.Ĭell-surface receptors represent an important class of membrane and membrane-associated proteins. The resulting membrane-bead pellet is treated with various detergents or chaotropic agents (i.e., urea) to elute bound proteins. Cells are subsequently ruptured, and segregation of the resulting plasma membrane sheets from the remaining cell constituents is achieved by ultracentrifugation through density gradients.

Electrostatic interactions between the beads and the negatively charged plasma membrane, followed by cross-linking to the membrane with an anionic polymer, ensure attachment and maintain the native protein conformation. The principle is simple – cationic colloidal silica microbeads are introduced to a suspension or monolayer of cells in culture.

Since then, this method has been successfully incorporated into a wide range of in vitro and in vivo applications for the isolation of cell-surface proteins. Chaney and Jacobson first introduced the colloidal silica-bead protocol for the coating of cellular plasma membranes in the early 1980s.

Silica beads