Color Tuning in Bovine Rhodopsin through Polarizable Embedding

Bovine rhodopsin is among the most studied proteins in
the rhodopsin
family. Its primary activation mechanism is the photoisomerization
of 11-cis retinal, triggered by the absorption of a UV–visible
photon. Different mutants of the same rhodopsin show different absorption
wavelengths due to the influence of the specific amino acid residues
forming the cavity in which the retinal chromophore is embedded, and
rhodopsins activated at different wavelengths are, for example, exploited
in the field of optogenetics. In this letter, we present a procedure
for systematically investigating color tuning in models of bovine
rhodopsin and a set of its mutants embedded in a membrane bilayer.
Vertical excitation energy calculations were carried out with the
polarizable embedding potential for describing the environment surrounding
the chromophore. We show that polarizable embedding outperformed regular
electrostatic embedding in determining both the vertical excitation
energies and associated oscillator strengths of the systems studied.