FOURIER-TRANSFORM INFRARED-SPECTROSCOPY REVEALS A RIGID ALPHA-HELICALASSEMBLY FOR THE TETRAMERIC STREPTOMYCES-LIVIDANS K+ CHANNEL

The structure of the tetrameric K+ channel from Streptomyces lividans in a lipid bilayer environment was studied by polarized attenuated tot al reflection Fourier transform infrared spectroscopy. The channel dis plays approximately 43% alpha-helical and 25% beta-sheet content. In a ddition, H/D exchange experiments show that only 43% of the backbone a mide protons are exchangeable with solvent. On average, the alpha-heli ces are tilted 33 degrees normal to the membrane surface. The results are discussed in relationship to the lactose permease of Escherichia c oli, a membrane transport protein.