Two-dimensional NMR study of the conformation of (34-65)bacterioopsin polypeptide in SDS micelles.

The conformation of the synthetic 32-residue polypeptide, an analog of the membrane spanning segment B (residues 34-65) of Halobacterium halobium bacterioopsin, incorporated into perdeuterated sodium dodecyl sulfate micelles in the presence of trifluoroethanol was investigated by 1H NMR spectroscopy. The spectrum resonances were assigned by means of phase-sensitive DQF-COSY, TOCSY and NOESY techniques. Interproton nuclear Overhauser effects and deuterium exchange rates of individual NH groups were derived from two-dimensional NMR spectra. Analysis of the obtained data showed that segment B has a right-handed alpha-helical stretch from Lys41 to Leu62 with a kink at Pro50. The alpha-helix in the C-terminal part is terminated at Gly63, which adopts a conformation typical of amino acid residues in a left-handed helix. The N-terminal part (residues 34-40) has no ordered conformation. NMR data are provided for comparison of the segment B conformation in the isotropic system of an organic solvent, in SDS micelles and in the purple membrane bacterioopsin. Factors affecting the conformation of membrane spanning segment B in various milieus are discussed.