Three-dimensional structure of (1–36)bacterioopsin in methanol—chloroform mixture and SDS micelles determined by 2D 1H-NMR spectroscopy

Abstract

Spatial structures of proteolytic segment A (sA) of bacterioopsin of H. halobium (residues 1–36) solubilized in a mixture of methanol—chloroform (1:1), 0.1 M LiClO 4 organic mixture, or in perdeuterated sodium dodecyl sulfate (SDS) micelles, were determined by 2D 1H-NMR techniques, 324 and 400 NOESY cross-peak volumes were measured in NOESY spectra of sA in organic mixture and SDS micelles, respectively. The sA spatial structures were determined by local structure analysis, distance geometry calculation with program DIANA and systematic search for energetically allowed side chain rotamers consistent with NOESY cross-peak volumes. The structures of sA are similar in both milieus and have the right-handed α-helical region from Pro ? to Met 32 with root mean square deviation (RMSD) of 0.25 Å between backbone heavy atoms and fit well with Pro ? to Met 32 α-helical region in electron cryo-microscopy model of bacteriorhodopsin. The N-terminal region Ala 2-Gly 4 of sA in organic mixture has a fixed structure of two consecutive γ-turns as 2 * 2 ?-helix (RMSD of 0.25 Å) stabilized by the Thr ? NH⋯O=C Gln 3 and Ile 4 NH⋯O=C Ala 2 hydrogen bonds while this region in SDS micelles has disordered structure with RMSD of 1.44 Å for backbone heavy atoms. The C-terminal region Gly 33-Asp ? of sA is disordered in both milieus. Torsion angles χ 1 of sA were unequivocally determined for 13 (SDS) and 11 (organic mixture) of α-helical residues and arc identical in both milieus.