Beyond the detergent effect: a binding site for sodium dodecyl sulfate (SDS) in mammalian apoferritin

Although sodium dodecyl sulfate (SDS) is widely used as an anionic detergent, it can also exert specific pharmacological effects that are independent of the surfactant properties of the similar to molecule. However, structural details of how proteins recognize SDS are scarce. Here, it is demonstrated that SDS binds specifically to a naturally occurring four-helix bundle protein: horse apoferritin. The X-ray crystal structure of the apoferritinSDS complex was determined at a resolution of 1.9 similar to angstrom and revealed that the SDS binds in an internal cavity that has previously been shown to recognize various general anesthetics. A dissociation constant of 24 +/- 9 similar to mu M at 293 similar to K was determined by isothermal titration calorimetry. SDS binds in this cavity by bending its alkyl tail into a horseshoe shape; the charged SDS head group lies in the opening of the cavity at the protein surface. This crystal structure provides insights into the proteinSDS interactions that give rise to binding and may prove useful in the design of novel SDS-like ligands for some proteins.