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Relocating the Active-Site Lysine in Rhodopsin: 2. Evolutionary Intermediates
Erin L Devine1, Douglas L Theobald1, Daniel D Oprian1
1Department of Biochemistry, Brandeis University , 415 South Street, Waltham, Massachusetts 02454, United States.
Biochemistry
|August 4, 2016
Summary
Rhodopsin can function with a second lysine residue in its active site, suggesting evolutionary pathways for this G protein-coupled receptor. This finding supports the possibility of lysine migration within the protein.
Area of Science:
- Biochemistry
- Molecular Biology
- Evolutionary Biology
Background:
- Rhodopsin, a G protein-coupled receptor, binds retinal via a Schiff base to a conserved lysine in helix 7.
- Previous studies showed bovine rhodopsin retains function when this lysine is moved to other sites.
Purpose of the Study:
- To investigate potential evolutionary intermediates of rhodopsin with two active-site lysine residues.
- To determine if rhodopsin can tolerate a second lysine in the retinal binding pocket.
Main Methods:
- Created four mutant rhodopsins with the original Lys296 and an additional lysine at positions G90K, T94K, S186K, or F293K.
- Assessed the ability of these mutants to bind retinal, form a pigment, and activate transducin.
Main Results:
- All four double-lysine mutants successfully bound 11-cis-retinal, formed pigments, and activated transducin in a light-dependent manner.
- Rhodopsin tolerates an additional lysine residue within the retinal binding pocket.
- Identified natural opsins (insect UV cones, neuropsins) with dual lysines and spectral similarities to mutants.
Conclusions:
- Rhodopsin's active site is more flexible than previously thought, allowing for a second lysine.
- The presence of two lysines could facilitate the evolutionary relocation of the Schiff base lysine.
- Natural opsins with dual lysines may represent intermediates or alternative functional states.
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