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Scientists have long known that light-sensitive proteins in the eye allow us to see color—from red strawberries to blue skies.
Now, researchers have uncovered how these molecules work at a fundamental level, offering clues that could help explain vision disorders.
In a new study published in Science, researchers led by Polina Isaikina and Sarah L. Schmidt at the Paul Scherrer Institute have, for the first time, mapped the three-dimensional structure of human “cone opsins” in their inactive, or dark, state.
Cone opsins are proteins in cone cells in the retina that enable color vision. When light enters the eye, these proteins capture it and trigger a rapid chain reaction that converts light into electrical signals, which are then sent to the brain as images.
Despite their importance, their precise structure has remained elusive because the proteins are highly unstable and can activate even in the absence of light.
To overcome this, the researchers worked under dim red light and used techniques including cryo-electron microscopy and ultrafast spectroscopy to capture detailed images of blue- and green-sensitive opsins. The study shows that cone opsins are built with a network of tiny internal “microswitches” that keep them in a ready-to-respond state, allowing the eye to process visual information almost instantly.
The team also found key structural differences between blue- and green-sensitive opsins. Green opsins appear more flexible, allowing them to respond to lower-energy light, while blue opsins have a tighter structure that requires higher-energy light to activate.
Asked how the findings might translate into real-world applications, Isaikina told Newsweek that the work remains in its early stages.
“Our study is basic fundamental research,” she said. “We describe the molecular architecture of the light-sensitive receptors that enable cone cells in the retina to detect different wavelengths and transmit signals rapidly in daylight.”
While the research does not point directly to new treatments, it could help scientists better understand what goes wrong in certain eye conditions.
“For color blindness, our structures may help researchers to suggest whether a disease-causing mutant disrupts retinal binding, impairs signaling or destabilizes the receptor fold,” Isaikina said. “In cases where mutations destabilize the protein’s fold, one future direction could be the design of small molecules to stabilize the receptor.”
She added that the findings are not a roadmap for immediate therapies and that the study “does not provide any treatment strategies.”
The research could still have long-term implications for conditions such as macular degeneration, which affects central vision.
“Because cones are essential for sharp central vision, understanding how cone photoreceptors maintain their light-sensitive machinery may eventually help efforts to preserve cone function in degenerative retinal disease,” Isaikina said.
The study also sheds light on why people may experience differences in color perception.
Humans have three types of cone opsins that detect different colors. They all use the same light-sensitive molecule, but the surrounding protein changes how it reacts to light. This could help researchers pinpoint how genetic mutations alter vision.
Importantly, the research suggests that many forms of color vision deficiency may involve broader structural issues, rather than just subtle shifts in color tuning.
“In the long term, this could help guide mutation-specific strategies to preserve or improve cone function,” Isaikina said.
Contact Newsweek editors on this story: Kara Dolman and Sam Wilson.
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