Characterisation of Schiff base and chromophore in green proteorhodopsin by solid-state NMR
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The proteorhodopsin family consists of hundreds of homologous retinal containing membrane proteins found in bacteria in the photic zone of the oceans. They are colour tuned to their environment and act as light-driven proton pumps with a potential energetic and regulatory function. Precise structural details are still unknown. Here, the green proteorhodopsin variant has been selected for a chemical shift analysis of retinal and Schiff base by solid-state NMR. Our data show that the chromophore exists in mainly all-trans configuration in the proteorhodopsin ground state. The optical absorption maximum together with retinal and Schiff base chemical shifts indicate a strong interaction network between chromophore and opsin.
KeywordsProteorhodopsin Solid-state NMR Schiff base Retinal
Protonated Schiff base
Magic angle sample spinning
This work has been financially supported by SFB 472 (“Molecular Bioenergetics”). Cells and plasmids were kindly provided by E. Bamberg, Frankfurt and M. Engelhard, Dortmund. The 10,11-13C2 retinal was a generous gift of Marina Carravetta and Malcolm Levitt, Southampton. Ute Hellmich and Christoph Kaiser are acknowledged for helpful discussions.
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