Chemistry, vol. 284, p.13562-13569 (2009).
The four stationary states of retinal isomerization :
(protonated Schiff-base (PSB) of the retinal in yellow)
A) All-trans ground state: the positively charged PSB makes favorable interactions with the nearby negative groups (chloride and Asp238).
B) Transition state ‡(Ser115) of the counter-clockwise route for cis→trans isomerization.
C) Transition state ‡(Asp238) of the clockwise route for cis→trans isomerization.
D) 13-cis planar K-state: the PSB makes poorer interactions with the negative groups than in A). This is the energy storage mechanism.
| Minimum Energy
Pathway (MEP) along a 360° rotation of the PSB:
QM/MM energy profile of the pathway through the four structures shown on the left:trans → ‡(Ser115) → 13‑cis→ ‡(Asp238) → trans
The total energy (continuous black line) is the sum of:
- the retinal self energy (in blue)
- the opsin self energy (everything excluding retinal, in red)
- and the interaction between retinal and the opsin (in green).
The arrows show the two possible decay routes of 13-cis.
Molecular movies showing these transitions are shown below.
Movie 1. Decay of
K-state via ‡(Asp238),
clockwise rotation of the PSB.
The energy barrier is 18 kcal/mol relative to the 13-cis K-state. This is the preferred route for 13-cis → trans backisomerisation.
Download the movie (0.4Mb)
Movie 2. Decay of K-state via ‡(Ser115),
counter-clockwise rotation of the PSB.
The energy barrier is 23 kcal/mol relative to the 13-cis K-state.
Download the movie (0.6Mb)
Movie 3. 360° rotation of the PSB, trans →
‡(Ser115) → 13‑cis→ ‡(Asp238) → trans.
Concatenation of movies 1 and 2. Same order of events as in the energy profile shown above.
Download the movie (0.9Mb)
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