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A rhodopsin exhibiting binding ability to agonist all-trans-retinal
Hisao Tsukamoto1, Akihisa Terakita, Yoshinori Shichida
1Department of Biophysics, Graduate School of Science, Kyoto University and Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kyoto 606-8502, Japan.
Summary
Amphioxus rhodopsin binds the agonist all-trans-retinal, unlike vertebrate rhodopsin. This ancestral protein
Area of Science:
- Molecular Evolution
- Biochemistry
- Photoreceptor Biology
Background:
- Rhodopsins are G protein-coupled receptors that function as photoreceptive pigments.
- Vertebrate rhodopsins bind 11-cis-retinal but not all-trans-retinal, indicating evolutionary changes in binding ability.
Purpose of the Study:
- To investigate the chromophore-binding properties of amphioxus rhodopsin.
- To understand the evolutionary transition of rhodopsin's ligand-binding capabilities.
Main Methods:
- Spectroscopic and biochemical analyses of amphioxus rhodopsin.
- Mutational analysis focusing on Trp-265 in helix VI.
Main Results:
- Amphioxus rhodopsin binds both 11-cis-retinal and all-trans-retinal.
- Binding of all-trans-retinal forms a G protein-activating state similar to the photoproduct.
- Amphioxus rhodopsin shows higher affinity for 11-cis-retinal, with Trp-265 being crucial for this preference.
Conclusions:
- Amphioxus rhodopsin retains ancestral agonist-binding ability, unlike its vertebrate counterparts.
- An evolutionary rearrangement involving Trp-265 likely enhanced 11-cis-retinal affinity in ancestral rhodopsins.
- Vertebrate rhodopsins evolved mechanisms to prevent all-trans-retinal binding.