Rhodopsin is a tunable capacitor buffering the toxic, desensitizing retinoids of the vertebrate eye

Visual sensitivity creates photodamage risk, a trade-off thought to limit photo-resilience. Here we reveal that the locus of sensitivity--the visual pigment rhodopsin--moonlights as a tunable mechanism of photoprotection. Light activated rhodopsin (R*) mitigates phototoxicity and boosts rod sensitivity by serving as an overflow capacitor buffering all-trans retinal (atRAL), a toxic and desensitizing retinoid agonist that accumulates as lipofuscin--a clinical marker of macular degeneration. We show that R* stability does not guarantee increased signaling as previously proposed. Instead, across mammals R* stability reflects atRAL binding affinity (capacitance) tuned by photodamage risk. R* cap