Mechanism of interaction of sodium dodecyl sulfate with mouse interferon.

Sodium dodecyl sulfate (SDS) and other alkyl sulfates, provided they contain a minimum of 12 carbon atoms (or 322 A in length), stabilize mouse interferon (MIF) in the presence of urea, 2-mercaptoethanol, and heat. When MIF is treated with the alkyl sulfates in the absence of urea and 2-mercaptoethanol, all alkyl sulfates inactivate MIF to the same extent. This suggests that the stabilizing effect of SDS on MIF most likely occurs during the refolding process. Unlike SDS, other amphiphiles such as dodecylamine, lithium dodecyl sulfate, and sodium 1-dodecane sulfonate did not have an appreciable stabilizing effect on MIF, thus emphasizing the necessity of specific counter-ions and polar groups for SDS to affect MIF stability. Subsequent to its reaction with SDS, MIF no longer binds to controlled pore glass (CPG) beads. This is most likely due to SDS masking the protein’s silanol-binding sites. Furthermore, after it has reacted with interferon, a portion (about 20 to 50%) of the SDS is no longer retained by the anion exchange resin AGl-X10. Conversely, interferon (which does not bind to AGl-X2, a resin with a larger pore size than AGl-X10) is retained by the resin AGl-X2 after it has reacted with SDS. In addition, SDS-treated MIF is able to bind to the immobilized hydrophobic ligand hexyl-agarose under conditions where the majority of the MIF itself is not retained. Inasmuch as some SDS co-elutes with MIF from AGlX10, it is concluded that SDS binds to MIF. Furthermore, since SDS-treated MIF is retained by AGl-X2 and hexyl-agarose, we assume that at least some of the detergent’s polar and hydrophobic regions are located at the surface of the interferon molecule.