STUDIES OF THE PORE-FORMING DOMAIN OF A VOLTAGE-GATED POTASSIUM CHANNEL PROTEIN

Recent mutagenesis studies have identified a stretch of amino acid res idues which form the ion-selective pore of the voltage-gated potassium channel. It has been suggested that this sequence of amino acids form s a P-barrel structure making up the structure of the ion-selective po re [Hartman,H.A., Kirsch,G.E., Drewe,J.A, Taglialatela,M., Joho,R.H. a nd Brown,A.M. (1991) Science, 251, 942-944; Yellen,G., Jurman,M.E., Ab ramson,T. and MacMirnon,R. (1991) Science, 251, 939-942; Yool,A.J. and Schwarz,T.L. (1991) Nature, 349, 700-704]. We have synthesized a poly peptide corresponding to this amino acid sequence (residues 431-449 of the ShA potassium channel from Drosophila). A tetrameric version of t his sequence was also synthesized by linking together four of these pe ptides onto a branching lysine core. Fourier transform infrared (FT-IR ) and circular dichroism (CD) spectroscopy have been used to investiga te the structure of these peptides after their reconstitution into lys o phosphatidylcholine micelles and lipid bilayers composed of dimyrist oyl phosphatidylcholine and dimyristoyl phosphatidylglycerol. The spec troscopic studies show that these peptides are predominantly alpha-hel ical in these lipid environments. When incorporated into planar lipid bilayers both peptides induce ion channel activity. Molecular modellin g studies based upon the propensity of these peptides to form an cu-he lical secondary structure in a hydrophobic environment are described. These results are discussed in the light of recent mutagenesis and bin ding studies of the Drosophila Shaker potassium ion channel protein.