cis $$ightarrow$$ → trans Isomerization of Bacteriorhodopsin’s Retinal Chromophore by a Hydrogen-Bond Network

摘要

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.