STRUCTURAL DYNAMICS OF THE STREPTOMYCES-LIVIDANS K- SECONDARY STRUCTURE CHARACTERIZATION FROM FTIR SPECTROSCOPY( CHANNEL (SKC1) )

Fourier transform infrared (FTIR) spectroscopy was used to probe the s econdary structure, orientation, and the kinetics of amide hydrogen-de uterium exchange (HX) of the small K+ channel from Streptococcus livid ans. Frequency component analysis of the amide I band showed that SKC1 is composed of 44-46% alpha-helix, 21-24% beta-sheet, 10-12% turns an d 18-20% unordered structures. The order parameter S of the helical co mponent of SKC1 was between 0.60 and 0.69. Close to 80% of SKC1 amide protons exchange within similar to 3 h of D2O exposure, suggesting tha t the channel is largely accessible to solvent exchange. These results are consistent with a model of SKC1 in which helices slightly tilted from the membrane normal line the water-filled vestibules that flank t he K+ selectivity filter. (C) 1998 Federation of European Biochemical Societies.