Studies of the pore-forming domain of a voltage-gated potassium channel protein

Recent mutagenesis studies have identified a stretch of amino acid residues which form the ion-selective pore of the voltage-gated potassium channel. It has been suggested that this sequence of amino acids forms a beta-barrel structure making up the structure of the ion-selective pore [Hartman, H.A., Kirsch, G.E., Drewe, J.A., Taglialatela, M., Joho, R.H. and Brown, A.M. (1991) Science, 251, 942-944; Yellen, G., Jurman, M.E., Abramson, T. and MacKinnon, R. (1991) Science, 251, 939-942; Yool, A.J. and Schwarz, T.L. (1991) Nature, 349, 700-704]. We have synthesized a polypeptide corresponding to this amino acid sequence (residues 431-449 of the ShA potassium channel from Drosophila). A tetrameric version of this sequence was also synthesized by linking together four of these peptides onto a branching lysine core. Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopy have been used to investigate the structure of these peptides after their reconstitution into lyso phosphatidylcholine micelles and lipid bilayers composed of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol. The spectroscopic studies show that these peptides are predominantly alpha-helical in these lipid environments. When incorporated into planar lipid bilayers both peptides induce ion channel activity. Molecular modelling studies based upon the propensity of these peptides to form an alpha-helical secondary structure in a hydrophobic environment are described. These results are discussed in the light of recent mutagenesis and binding studies of the Drosophila Shaker potassium ion channel protein.