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Title: Solid-state nuclear magnetic resonance of rhodopsin and its photointermediates
Author: Concistre, Maria
ISNI:       0000 0004 2695 4777
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2010
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Photoisomerization of the membrane-bound light receptor protein rhodopsin leads to a highly energetic species called bathorhodopsin, which is stable at temperatures below 125 K. Bathorhodopsin stores about 2/3 of the absorbed photon energy but the mechanisms with which this energy is stored is not completely understood. A new insight into these mechanisms by means of low-temperature solid-state NMR is both subject and aim of this Ph.D. thesis. The issue of the energy storage has been investigated by a solid state magic angle spinning technique which combines modern symmetry-based recoupling techniques with in situ cooling of the sample. Production of bathorhodopsin is also done in situ in a customized NMR probe. Three kind of experiments are discussed: chemical shift, distance and torsional angle measurements. The first kind of experiments led to carbon chemical shifts values for almost all the carbons along the retinylidene chain of the retinal chromophore of bathorhodopsin. Our measurements show a significant perturbations of the 13C chemical shifts in bathorhodopsin which is interpreted in terms of charge delocalization along the chain and therefore indicates a participation of an electrostatic mechanism to the energy storage. This is at variance with an earlier solid state NMR study where only minor perturbations of the electronic structure in the isomerized retinylidene chain were observed. We believe that these data incorrectly refer to bathorhodopsin because of the incorrect conditions of temperature and illumination applied. To sample for other local mechanisms that may contribute to the energy storage, the C-C distance of the last two carbons of the retinylidene chain, at the link with the protein opsin, was also measured but no significant differences with rhodopsin have been found. Finally, the H-C=C-H torsional angle at the double bound where the isomerization takes place was measured in a double-quantum heteronuclear local field spectroscopy (2Q-HLF) experiment. Results indicate a deviation from planarity of at least 40˚ about this double bond in bathorhodopsin suggesting an unquantified amount of torsional strain acting as a further energy storage mechanism. In addition to these very interesting results, this thesis reports methods, equipment and procedures ready to be used for the study of other similar light-triggered processes.
Supervisor: Levitt, Malcolm Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry