Removal of Detergent From Protein Fractions

Abstract

The solubilization of biological membranes by detergents plays an important role in the identification, characterization, and extraction of integral membrane proteins. The solubilization process involves a number of intermediate states starting with the desta-bilization of membrane lipids and followed by the creation of membrane fragments, which finally results in the formation of protomers (1). The most commonly used detergents in the biological sciences are described in Chapter 29 and several review articles exist on solubilization procedures (2–4). Because the initial extraction of intrinisic membrane proteins usually involves high detergent concentrations, excess detergent has to be removed or exchanged for another type of detergent at later stages of preparative or analytical procedures involving the solubilized protein fraction. The efficiency of certain chromatographic procedures is often significantly improved by lowering the overall detergent concentration or by exchanging one type of detergent for another. Lectin chromatography, a powerful technique to affinity-purify subsets of glycoproteins (see Chapter 18), appears to be especially sensitive to high concentrations of a variety of detergents (5). Furthermore, because high concentrations and/or certain types of detergent interfere with many physical and chemical analyses and detergents also exhibit undesirable side effects on highly sensitive cell biological assays, detergent removal is, in many cases, of central importance for retaining the biological activity of isolated membrane proteins. Another important area of detergent removal is reconstitution studies with hydrophobic membrane proteins that exhibit vectorial transport (4).