Empigen BB: a useful detergent for solubilization and biochemical analysis of keratins

Intermediate filament (IF) proteins make up some of the most insoluble proteins known, and within the IF protein family, keratins are the least soluble. We compared the efficiency of nonionic, cationic, mixed nonionic and anionic, and zwitterionic detergents in solubilizing keratins from insect cells that express recombinant human keratins and from human colonic cell lines and normal keratinocytes. The cationic detergent cetyltrimethylammonium bromide was similar to the zwitterionic detergent Empigen BB in its ability to efficiently solubilize keratins, but the latter detergent was superior in that it maintained antibody reactivity and allowed for immunoprecipitation of the keratins. Although Nonidet-P40 partially solubilizes keratins, Empigen BB solubilizes a significant amount of keratins not solubilized by Nonidet-P40. In the case of vimentin, differences in solubilization efficiency among the detergents was not as dramatic as with keratins. Our results show that Empigen BB solubilizes a significant amount of epidermal and glandular keratins while preserving antigenicity. This detergent should prove useful for carrying out biochemical and molecular studies on these proteins and may be similarly beneficial for other IF proteins.