Participation of the surface structure of pharaonis phoborhodopsin, ppR and its A149S and A149V mutants, consisting of the C-terminal α-helix and E-F loop, in the complex-formation with the cognate transducer pHtrII, as revealed by site-directed 13C solid-state NMR
We have recorded 13C solid state NMR spectra of [3-13C]Ala-labeled pharaonis phoborhodopsin ppR, and its mutants, A149S and A149V, complexed with the cognate transducer pHtrII (1-159), to gain insight into a possible role of their cytoplasmic surface structure including the C-terminal α-helix and E-F loop for stabilization of the 2:2 complex, by both cross-polarization magic angle spinning (CP-MAS) and dipolar decoupled-magic angle spinning (DD-MAS) NMR techniques. We found that 13C CP-MAS NMR spectra of [3-13C]Ala-ppR, A149S, and A149V complexed with the transducer pHtrII are very similar, reflecting their conformation and dynamics changes caused by mutual interactions through the transmembrane α-helical surfaces. In contrast, their DD-MAS NMR spectral features are quite different between [3-13C]Ala- A149S and A149V in the complexes with pHtrII: 13C DD-MAS NMR spectrum of [3-13C]Ala-A149S complex is rather similar to that of the uncomplexed form, while the corresponding spectral feature of A149V complex is similar to that of ppR complex in the C-terminal tip region. This is because more flexible surface structure detected by the DD-MAS NMR spectra are more directly influenced by the dynamics changes than the CP-MAS NMR. It turned out, therefore, that an altered surface structure of A149S resulted in destabilized complex as viewed from the 13C NMR spectrum of the surface areas, probably because of modified conformation at the corner of the helix F in addition to the change of hydropathy. It is, therefore, concluded that the surface structure of ppR including the C-terminal α-helix and the E-F loops is directly involved in the stabilization of the complex through conformational stability of the helix F.
Photochemistry and Photobiology
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American Society of Photobiology
Author Posting. (c) The Authors (2007) This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in PHOTOCHEMISTRY AND PHOTOBIOLOGY, 83(2): 339-345. http://dx.doi.org/10.1562/2006-06-20-RA-940