CONFORMATIONAL-CHANGES IN A MAMMALIAN VOLTAGE-DEPENDENT POTASSIUM CHANNEL INACTIVATION PEPTIDE

Fast inactivation is restored in inactivation deletion mutant voltage- gated potassium (K-v) channels by application of synthetic inactivatio n 'ball' peptide. Using Fourier transform infrared and circular dichro ism spectroscopy, we have investigated the structure of synthetic K(v) 3.4 channel ball peptide, in a range of environments relevant to the f unction of the ball domain. The ball peptide contains no alpha-helix o r beta-sheet in reducing conditions in aqueous solution, but when coso lubilized with anionic lipid or detergent in order to mimic the enviro nment which the ball domain encounters during channel inactivation, th e ball peptide adopts a partial beta-sheet structure. Oxidation of the K(v)3.4 ball peptide facilitates formation of a disulfide bond betwee n Cys(6) and Cys(24) and adoption of a partial beta-sheet structure in aqueous solution; the tendency of the oxidized ball peptide to adopt beta-sheet is generally greater than that of the reduced ball peptide in a given environment. THREADER modeling of the K(v)3.4 ball peptide structure predicts a beta-hairpin-like conformation which corresponds well to the structure suggested by spectroscopic analysis of the ball peptide in its cyclic arrangement, A V7E mutant K(v)3.4 ball peptide a nalogue of the noninactivating Shaker B L7E mutant ball peptide cannot adopt beta-structure whatever the environment, and regardless of oxid ation state. The results suggest that the K(v)3.4 ball domain undergoe s a conformational change during channel inactivation and may implicat e a novel regulatory role for intramolecular disulfide bond formation in the K(v)3.4 ball domain in vivo.