[Spatial structure of bacterioopsin 87-136 fragment]

The [Nle18]-(87-136)-bacterioopsin, a fragment of bacterioopsin from Halobacterium salinarium synthesized by solid phase technique, was solubilized in a 1:1 chloroform-methanol mixture containing 0.1 M LiClO4 and studied by two-dimensional 1H NMR spectroscopy. The complete assignment of proton resonances was performed in the DQF-COSY, TOCSY, and NOESY spectra of this peptide, and its spatial structure was computed. As a result, two helical regions (92-100 and 108-130) were identified, which correspond to the C-terminal part of segment C and to segment D of bacteriorhodopsin, respectively. The 92-100 region forms a right-handed alpha-helix, and the 108-130 region can adopt right-handed alpha-helical, 3(10)-helical, and combined (from the two) conformations. A comparison of the structure computed with the bacteriorhodopsin model deduced from the electron cryomicroscopy data showed good agreement in the 91-100 region (the root-mean-square deviation of the backbone atoms was less than 0.51 A) and considerable differences in the 108-130 region (1.82 A). A dynamic model of the conformation of the D transmembrane segment was suggested, and the accordance of the model to the functional dynamics of bacteriorhodopsin was discussed.