Peptides modeled on the transmembrane region of the slow voltage-gated IsK potassium channel: Structural characterization of peptide assemblies in the beta-strand conformation

A 27-residue peptide, having a sequence corresponding to the transmembrane domain of the IsK protein with slow voltage-gated potassium channel activity, has been incorporated into synthetic saturated-chain phospholipid membranes. The peptide−lipid complexes have been characterized by attenuated-total-reflection Fourier-transform-infrared spectroscopy (ATR-FTIR), spin-label electron spin resonance (ESR) spectroscopy, 31P and 2H nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry, and low-angle X-ray diffraction. From FTIR spectroscopy, it is found that, when reconstituted into membranes by dialysis from 2-chloroethanol, the peptide has a predominantly β-strand secondary structure in which the peptide backbone is oriented at an angle of approximately 56° relative to the membrane normal in dry films of phosphatidylcholines. Hydration of the dry film in the gel phase does not appear to affect the orientation of the peptide backbone, and a relatively small change in orientation occ...