Cationic detergents are the type of ionic detergents that have a positive charge. The cationic part of these detergents contains a long hydrocarbon chain and a positively charged nitrogen atom. In the case of cationic part, a quaternary ammonium headgroup (e.g., trimethylammonium group) is most common (e.g., cetyltrimethylammonium bromide (CTAB)). Cationic detergents generally have higher critical micelle concentration (CMC) values and tend to be fairly harsh. The size of cationic detergents micelle depends on the hydrophobic attraction of the side chain and the repulsion of the ionic group. Thus, larger micelle can be formed by increasing the concentration of countervailing ions that neutralize the charge on the head group. Furthermore, additional precautions should be taken when using cationic detergents because some of their properties may be altered in buffers with variable ionic strength (e.g., CMC can fall dramatically when the NaCl concentration increases from 0 to 500 mM).
Fig. 1. The chemical structures of CTAB.
Cationic detergents have a wide range of applications in biology. For examples, gene molecules can be individually compacted by cationic thiol detergents into nanometric particles that are stabilized by oxidative conversion of the detergent into a gemini lipid, so as to achieve effective cell transfection . The rate of renaturation for complementary DNA strands can be enhanced greater than 10(4)-fold by the addition of simple cationic detergents . Glycosaminoglycans (GAGs) can be well immobilized on membranes after cationic detergent treatment, which can be used in solid-phase extraction of GAGs in blood plasma, urine, or cerebrospinal fluid .
Of course, detergents are mainly used in the study of membrane proteins. In the study of membrane proteins, cationic detergents are very effective in solubilizing membrane proteins. However, they inevitably cause more or less denaturation. Even so, it played an important role in the early study of membrane proteins. This is very similar to anionic detergents. Today, alternative two-dimensional gel electrophoresis (2-DE) methodologies, for instance combining SDS-PAGE based on the usage of cationic detergents like benzyldimethyl 16-benzyldimethyl-n-hexadecylammonium chloride (16-BAC) or CTAB, have gained more attention in membrane proteins study. The technologies are known as 16-BAC/SDS-PAGE and CTAB/SDS-PAGE, respectively. Since 16-BAC and CTAB are potent ionic detergents that are suitable for solubilizing hydrophobic membrane proteins, these approaches are highly valuable for separating membrane proteins. 16-BAC/SDS-PAGE is now successfully used as an effectively tool for the separation of (integral) membrane proteins from various biological sources. Zahedi and colleagues, for instance, performed a proteomic analysis of purified yeast mitochondria by applying 16-BAC/SDS-PAGE. Forty-two integral membrane proteins were identified exclusively by the 16-BAC/SDS-PAGE approach. Coughenour and colleagues analyzed the rat synaptic vesicle proteome by 16-BAC/SDS-PAGE, and twelve membrane proteins were identified by the 16-BAC/SDS-PAGE approach. Moreover, membrane proteins identified solely with 16-BAC/SDS-PAGE demonstrated significantly higher hydrophobicity, as gauged by increased GRAVY indices and an increased number of transmembrane domains. These examples underline the usefulness of 16-BAC/SDS-PAGE for the separation of membrane proteins with increased hydrophobicity. The isolated membrane proteins have high resolution and can be used in subsequent studies .
Fig. 2. Scheme of a two-dimensional 16-BAC/SDS PAGE using slab gels.
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- Dauty E., et al. Dimerizable cationic detergents with a low cmc condense plasmid DNA into nanometric particles and transfect cells in culture[J]. Journal of the American Chemical Society, 2001, 123(38): 9227-9234.
- Pontius B. W. and Berg P. Rapid renaturation of complementary DNA strands mediated by cationic detergents: a role for high-probability binding domains in enhancing the kinetics of molecular assembly processes[J]. Proceedings of the National Academy of Sciences, 1991, 88(18): 8237-8241.
- Karlsson M., et al. Binding and detection of glycosaminoglycans immobilized on membranes treated with cationic detergents[J]. Analytical biochemistry, 2000, 286(1): 51-58.
- Braun R. J., et al. Two-dimensional electrophoresis of membrane proteins[J]. Analytical and bioanalytical chemistry, 2007, 389(4): 1033-1045.
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