Backbone Dynamics in the Transmembrane a-Helices

Based on the site-directed mutants together with the Mn -induced spectral editing described in Section 3.4, the C NMR positive peak at 17.27 ppm in the difference 

The three Pro residues that serve as the kinked structures in PM are located in the inner part of the transmembrane a-helices. Pro 186 (helix F), Pro 50 (helix B), and Pro 91 (helix C) among the total 10 Pro residues, as pointed out already in Section 4.1. It is emphasized that the acquired protein dynamics due to the presence of the kinked structure and its physiological significance can be visualized by solid-state NMR alone. This aspect will be discussed in more detail in the following section. 

Photoisomerization of the retinal from the ] -trans to the l3-cis form initiates proton transfer steps from the cytoplasmic to the extracellular side via the J, K, L, M, N, and O intermediates of a cyclic reaction.These intermediate states can be distinguished over picosecond to millisecond ranges, and a series of the cycle is completed in less than 10 ms. Global conformational changes of the protein 

It is expected that such global conformational as well as concomitant dynamic changes, if any, could be suitably examined by the site-directed solid-state NMR 

Undoubtedly, acquisition of such fluctuation motion at the cytoplasmic side of the transmembrane B and C a-helices in the M-like state of D85N mutant (Fig. 24B) is responsible for a transient environmental change from the hydrophobic to hydrophilic conditions both at the Asp 96 and Schiff base (SB) as compared with the ground state (Fig. 24A), resulting in a reduced pAa value of Asp 96 in the M-like state, which makes proton uptake more efficient. Further, it is demonstrated that the presence of the van der Waals contact of Val 49 with Lys 216 at the Schiff base is essential to trigger this sort of dynamic change, as revealed from the NMR 

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