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Catalysis of Ground State cis[Formula: see text] trans Isomerization of Bacteriorhodopsin's Retinal Chromophore by a
Nadia Elghobashi-Meinhardt1, Prasad Phatak2,3, Ana-Nicoleta Bondar4
1Department of Physical and Theoretical Chemistry, Theoretical Molecular Biophysics, Institute for Chemistry und Biochemistry, Freie Universität Berlin, Fabeckstr. 36a, Berlin, 14169, Germany. nadia.elghobashi-meinhardt@fu-berlin.de.
Abstract:
For the photocycle of the membrane protein bacteriorhodopsin to proceed efficiently, the thermal 13-cis to all-trans back-isomerization of the retinal chromophore must return the protein to its resting state on a time-scale of milliseconds. Here, we report on quantum mechanical/molecular mechanical energy calculations examining the structural and energetic determinants of the retinal cis-trans isomerization in the protein environment. The results suggest that a hydrogen-bonded network consisting of the retinal Schiff base, active site amino acid residues, and water molecules can stabilize the twisted retinal, thus reducing the intrinsic energy cost of the cis-trans thermal isomerization barrier.