Synthetic peptide fragments as probes for structure determination of potassium ion-channel proteins

Potassium channels are a diverse class of transmembrane proteins that are r esponsible for diffusion of potassium ion across cell membranes. The lack o f large quantities of these proteins from natural sources, is a major hindr ance in their structural characterization using biophysical techniques. Syn thetic peptide fragments corresponding to functionally important domains of these proteins provide an attractive approach towards characterizing the s tructural organization of these ion-channels. Conformational properties of peptides from three different potassium channels (Shaker, ROMK1 and minK) h ave been characterized in aqueous media, organic solvents and in phospholip id membranes. Techniques used for these studies include FTIR, CD and 2D-NMR spectroscopy. FTIR spectroscopy has been a particularly valuable tool for characterizing the folding of the ion-channel peptides in phospholipid memb ranes; the three different types of potassium channels all share a common t ransmembrane folding pattern that is composed of a predominantly alpha-heli cal structure. There is no evidence to suggest the presence of any signific ant beta-sheet structure. These results are in excellent agreement with the crystal structure of a bacterial potassium channel (Doyle, D. A. et nl. (1 998) Science 280:69-77), and suggest that all potassium channel proteins ma y share a common folding motif where the ion-channel structure is construct ed entirely from a-helices.