The stability of cell surface protein to surfactants and denaturants

The effects of several denaturants and detergents on the structure and stability of cell surface protein have been evaluated by circular dichroism and fluorescence measurements. Cell surface protein undergoes a single broad transition in both urea and guanidinium chloride. Although guanidinium chloride is twice as effective as urea on a molar basis, both appear to eliminate all of the organized structure present in the native molecule. Nonionic surfactants and lysolecithin have little effect on cell surface protein. However, sodium dodecyl sulfate increases the alpha helical content and cetyltrimethylammonium bromide increases the beta structure of cell surface protein. The reorganization of the polypeptide backbone requires the loss of certain restraints imposed by tertiary interactions as evidenced by a decrease in ellipticity in the far ultraviolet and in the polarization of tryptophanyl fluorescence. These results along with the data of a previous paper (Alexander, S. S., Jr., Colonna, G., Yamada, K. M., Pastan, I., and Edelhoch, H. (1978) J. Biol. Chem. 253, 5820--5824) suggest the presence of structural domains distributed along the flexible polypeptide chain of cell surface protein.