Photocyclic behavior of rhodopsin induced by an atypical isomerization mechanism.
basic_science · Level V
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- Record sourced from PubMed, PMID 28289214.
- Also identified by DOI 10.1073/pnas.1617446114 and PMC identifier 5380078.
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Abstract
Vertebrate rhodopsin (Rh) contains 11-<i>cis</i>-retinal as a chromophore to convert light energy into visual signals. On absorption of light, 11-<i>cis</i>-retinal is isomerized to all-<i>trans</i>-retinal, constituting a one-way reaction that activates transducin (G<sub>t</sub>) followed by chromophore release. Here we report that bovine Rh, regenerated instead with a six-carbon-ring retinal chromophore featuring a C<sup>11</sup>=C<sup>12</sup> double bond locked in its <i>cis</i> conformation (Rh6mr), employs an atypical isomerization mechanism by converting 11-<i>cis</i> to an 11,13-<i>dicis</i> configuration for prolonged G<sub>t</sub> activation. Time-dependent UV-vis spectroscopy, HPLC, and molecular mechanics analyses revealed an atypical thermal reisomerization of the 11,13-<i>dicis</i> to the 11-<i>cis</i> configuration on a slow timescale, which enables Rh6mr to function in a photocyclic manner similar to that of microbial Rhs. With this photocyclic behavior, Rh6mr repeatedly recruits and activates G<sub>t</sub> in response to light stimuli, making it an excellent candidate for optogenetic tools based on retinal analog-bound vertebrate Rhs. Overall, these comprehensive structure-function studies unveil a unique photocyclic mechanism of Rh activation by an 11-<i>cis</i>-to-11,13-<i>dicis</i> isomerization.
Medical subject headings
- Rhodopsin