Download MendeleyBiophysical and structural analysis of human green cone opsin.
Yao, W., Fay, J.F., Farrens, D.L.(2026) Biophys J
- PubMed: 41832604 Search on PubMed
- DOI: https://doi.org/10.1016/j.bpj.2026.03.029
- Primary Citation Related Structures:
9YGZ - PubMed Abstract:
We describe a straightforward method for purifying and optimizing human green cone opsin (GCO), which we then used for biophysical and structural studies of a GCO mutant, GCO E129Q . Our results show that in dark-state GCO, residue E129 enables long-wavelength light absorption, presumably by acting as the counterion for the protonated retinal Schiff base. Notably, the Schiff base pKa in dark-state GCO E129Q appears to be markedly lower (pKa ≈4) than in the rhodopsin equivalent, Rho E113Q (pKa ≈7), indicating distinct electrostatic environments at the retinal attachment site. Functional studies show that light-activated GCO E129Q decays more slowly and activates more G-protein than wild-type GCO (GCO WT ). To identify the basis for these differences, we determined the structure of active GCO E129Q bound to a G-protein. We first developed a streamlined workflow to identify conditions that enhance GCO E129Q binding to G-proteins. This approach involved screening GCO E129 binding to Gα-CT resin (beads bearing tethered Gα C-terminal peptides), followed by small-scale pull-down assays using 1D4 antibody beads to detect co-purification of GCO E129 with a Venus-tagged mini-G-protein. Using the optimized conditions, we determined a 3.0-Å cryo-EM structure of the GCO E129 -G-protein complex. Comparison with rhodopsin and our recent 3.0-Å structure of GCO WT reveals that the active-state architectures are largely similar, with several intriguing differences. Together, these results establish a generalizable, streamlined approach for biophysical and structural analysis of cone opsins and provide new mechanistic insight into the activation and signaling properties of GCO.
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, Oregon.
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