Figure 1
From: Modulation of thermal noise and spectral sensitivity in Lake Baikal cottoid fish rhodopsins
Rhodopsin structure and point-charge model.
(a) Crystallographic structure of Rh. The amino acid of Rh belong either to the “cavity” or “extra-cavity” region. (b) Structure of the Rh Lys296-Chromophore (green-blue) and its cavity (red) comprising the conserved E113 counterion. (c) Structure of the A1 (11-cis retinal) and A2 (11-cis 3-dehydroretinal) chromophores. The arrows indicates the double-bond isomerization triggering the pigment function. (d) Effect of a negative (red) point charge located in proximity of the chromophore β-ionone ring. The charge would stabilize the electronically photo-excited state (S1) dominated by a charge-transfer electronic configuration (ϕCT) with respect to the ground state (S0) dominated by a covalent electronic configuration (ϕCOV) leading to an increase in λmax (i.e. a decrease in ΔE as shown in the red energy level diagram on the right). A charge of the opposite sign placed in the same location would lead to the opposite effect (blue energy level diagram). (e) Relationship between the ΔE (proportional to 1/λmax) and the EaT controlling the chromophore thermal isomerization according to the point-charge model of ref. 8. A schematic representation of the chromophore charge distribution at the transition state (TS) is also given. The same negative/positive point charge would decrease/increase the barrier respectively.
