TOPOLOGY OF THE SHAKER POTASSIUM CHANNEL PROBED WITH HYDROPHILIC EPITOPE INSERTIONS

The structure of the Shaker potassium channel has been modeled as pass ing through the cellular membrane eight times with both the NH2 and CO OH termini on the cytoplasmic side (Durrell, S.R., and H.R. Guy. 1992. Biophys. J. 62:238-250). To test the validity of this model. we have inserted an epitope consisting of eight hydrophilic amino acids (DYKDD DDK) in predicted extracellular and intracellular loops throughout the channel. The channels containing the synthetic epitope were expressed in Xenopus oocytes, and function was examined by two-electrode voltag e clamping. All of the mutants containing insertions in putative extra cellular regions and the NH2 and COOH termini expressed functional cha nnels, and most of their electrophysiological properties were similar to those of the wild-type channel. Immunofluorescent staining with a m onoclonal antibody against the epitope was used to determine the membr ane localization of the insert in the channels. The data confirm and c onstrain the model for the transmembrane topology of the voltage-gated potassium channel.