[NMR paper] The Structural Basis of the Green-Blue Color Switching in Proteorhodopsin determined by NMR Spectroscopy.

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The Structural Basis of the Green-Blue Color Switching in Proteorhodopsin determined by NMR Spectroscopy.

The Structural Basis of the Green-Blue Color Switching in Proteorhodopsin determined by NMR Spectroscopy.

J Am Chem Soc. 2014 Nov 21;

Authors: Mao J, Do NN, Scholz F, Reggie L, Mehler M, Lakatos A, Ong YS, Ullrich SJ, Brown LJ, Brown RC, Becker-Baldus J, Wachtveitl J, Glaubitz C

Abstract
Proteorhodopsins (PRs) found in marine microbes are the most abundant retinal-based photoreceptors on this planet. PR variants show a high level of environmental adaptation as their color is tuned to the optimal wavelength of available light. The two major green and blue subfamilies can be interconverted through a L/Q point mutation at position 105. Here, we reveal the structural basis behind this intriguing color tuning effect. High-field solid-state NMR has been used to visualize structural changes within green PR directly within the lipid bilayer upon introducing the green-blue L105Q mutation. The observed effects are localized within the binding pocket and close to retinal carbons C14 and C15. Subsequently, MAS-NMR sensitivity-enhanced by dynamic nuclear polarization has been applied to determine precisely the retinal structure around C14-C15. Upon mutation, a significantly stretched C14-C15 bond, a deshielding of C15 and a slight alteration of the retinal chain's out-of-plane twist has been observed. The L105Q blue switch therefore acts locally on the retinal itself and induces a conjugation defect between isomerization region and imine linkage. Consequently, the S0-S1 energy gap increases resulting in the observed blue shift. The distortion of the chromophore structure also offers an explanation for the elongated primary reaction detected by pump-probe spectroscopy, while chemical shift perturbations within the protein can be linked to the elongation of late photocycle intermediates studied by flash photolysis. Besides of resolving a long-standing problem, this study also demonstrates that the combination of data obtained from high field and DNP-enhanced MAS-NMR together with time-resolved optical spectroscopy enables powerful synergies for in-depth functional studies of membrane proteins.


PMID: 25415762 [PubMed - as supplied by publisher]



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