Probing pore topology and conformational changes of Kir2.1 potassium channels by cysteine scanning mutagenesis

Using cysteine (Cys) scanning mutagenesis of the inward rectifier K+ channel Kir2.1, we investigated its pore structure and putative conformational changes. In the background of the Kir2.1 mutant C149F which showed no sensitivity towards Cys-modifying reagents, Cys residues were introduced at 10 positions in the H5 pore region. Out of six functional mutants, T141C and F147C showed clear changes in current amplitude when Cys-modifying reagents were applied from the external side. These results suggest that the corresponding sections of the H5 pore region face to the external side which is in contrast to the results previously obtained for voltage-gated K+ (Kv) channels. Using the mutants T141C and F147C, we investigated whether or not Kir2.1 channels show state-dependent conformational changes of the pore structure. Substantial alterations of the holding potential or external K+ concentration, however, did not cause any significant change in the speed of channel modification upon application of Cys-specific reagents, suggesting that Kir2.1 channels do not undergo conformational changes, in contrast to C-type inactivating Kv channels.