Detergent molecules consist of two parts: an extended, hydrophobic hydrocarbon moiety, and a polar or charged headgroup. Therefore, an anionic detergent refers to a detergent with an anionic charge on the headgroup. A sulfate group is the most popular as an anionic headgroup, as exemplified by sodium dodecyl sulfate (SDS), followed by sulfonate and carboxylate (e.g., sodium deoxycholate). Anionic detergents have the advantages of simple design and synthesis and strong membrane dissolving ability. However, their interaction with proteins is too strong, which can destroy the interaction between intramolecular or intermolecular proteins and cause the protein denaturation, making it difficult to obtain proteins with stable structure. Thus, they are mostly used in some studies with low requirements on protein advanced structure. Other application of anionic detergents is mainly on separation and purification technology such as gel electrophoresis.
Common Anionic Detergents
The most common anionic detergents are SDS, sodium lauryl sarcosinate, sodium deoxycholate and sodium cholate.
- SDS: SDS is the sodium salt of the 12-carbon an organosulfate. The anionic SDS is a very commonly used and effective surfactant in solubilizing most proteins. At the same time, it is very effective for disrupting non-covalent bonds within and between proteins. In the early years, due to its lipid-like amphipathic character, SDS has substantially increased out knowledge of membrane proteins and thus indirectly knowledge of membrane structure. However, SDS cannot be used when active proteins are required or when protein-protein interactions are being studied because both of these are disrupted by the SDS. When working with SDS, it is important to know that SDS precipitates at low temperatures, and this effect is enhanced in the presence of potassium salts. This phenomenon can sometimes be exploited to remove SDS from a protein sample . In addition, SDS is widely used in SDS polyacrylamide gel electrophoresis (SDS-PAGE).
Fig. 1. The structures of SDS.
- Sodium lauryl sarcosinate: Sodium lauroyl sarcosinate, also known as sarkosyl, is amphiphilic due to the presence of hydrophobic 14-carbon chain (lauroyl) and the hydrophilic carboxylate. The anionic detergent is widely used in laboratory experiments because of its high foam stability, excellent water solubility, and strong sorption capacity to proteins, for example, for solubilizing tau in Alzheimer disease research. In addition, Sarkosyl serves as a detergent to permeabilize cells and extract proteins in isolation and purification techniques such as western blotting and indirect enzyme-linked immunosorbent assay (ELISA). It can also inhibit the initiation of DNA transcription.
- Sodium deoxycholate and sodium cholate: Sodium deoxycholate and sodium cholate are bile salts detergents. Although, they are both anionic detergents, they are more moderate than linear anionic detergent (such as SDS and sarkosyl) due to their skeleton with rigid steroids. These two detergents are often used for membrane disruption and membrane protein extraction, for example, apelin receptor. One potential benefit to both of these two detergents is that they can be removed from samples via dialysis because of their fairly small micelle sizes, which may help with quantification and/or downstream analyses of proteins.
Fig. 2. The structures of sodium deoxycholate and sodium cholate.
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- Johnson M. Detergents: Triton X-100, tween-20, and more[J]. Mater Methods, 2013, 3(1): 163.
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