A global research team has reported the atomic structures of the light-sensitive molecules in the human eye that enable colour vision, a finding published in Science.
“To understand how we detect light and perceive colours, we need to know the exact structure of light-sensitive molecules in our eyes,” said The Australian National University (ANU) researcher Emeritus Professor Trevor Lamb.
“Our perception of colour is mainly determined by the relative excitation of red, green, and blue-sensitive cone photoreceptor cells found inside our retinas, that contain these molecules.”
The work involved scientists from research institutions in China, Germany and Australia. At ANU’s John Curtin School of Medical Research, Lamb focused on interpreting how the molecules function in the eye.
According to the researchers, the molecules—known as cone opsins—occur in three forms that convert red, green or blue light into chemical signals.
“Revealing the atomic structures for each of the molecules in their light-activated state shows how they work inside cone cells to trigger signals that are ultimately sent to the brain,” said Professor Lamb.
“Our results reveal fundamental differences between the cone opsins when they enter their active state after being hit with light.”
The researchers said fast activation and deactivation of these colour-detecting molecules is thought to support sharp vision and accurate perception of colour in motion in daylight.
All three cone opsins contain the same vitamin A-derived, light-sensitive molecule, retinaldehyde, but bind to it differently, the release said.
“Our study provides a molecular understanding of how each cone opsin interacts with retinaldehyde to tune it to different wavelengths of light,” said Professor Lamb.
“The red and green opsins appear to use very different placement of chemical electronic charges around the retinaldehyde. We suspect this difference explains how they shut off faster than the blue opsin, and much faster than the rod pigment.”
The structure of the rod pigment molecule used for low-light vision was solved decades ago, but the cone opsins have been harder to study, the researchers said, because they could not be crystallised using earlier approaches.
“It’s taken so long because it hasn’t been possible to make crystals of cone opsins,” said Professor Lamb. “Instead, our work used flash-frozen samples of each opsin, which are then examined by electron microscopy.”
Over the longer term, the findings could inform research into treatments for conditions including cone dystrophies and altered colour vision, according to the release.
“In many cases, cone vision disorders result from problems with the cone opsins,” said Professor Lamb.
Understanding the structure of cone opsins is important because it helps explain exactly how these disorders arise at a molecular level.
The study is published in Science.
