"The findings, which resolve a long-standing scientific question, were published in the journal Science."
A Breakthrough in Color Vision
An international research team has determined the atomic structures of the three human cone opsins, the light-sensitive proteins responsible for color vision.
Research Details
The study, titled "Cryo-electron microscopy structures of human cone visual pigments," was conducted by researchers from China, Germany, and Australia. Emeritus Professor Trevor Lamb from the Australian National University (ANU) contributed to interpreting the role of these molecules.
The team used cryo-electron microscopy to visualize the proteins in their light-activated state. This method circumvented previous difficulties associated with crystallizing cone opsins.
Molecular Structure and Function
Humans have three types of cone opsins, each located in red-, green-, and blue-sensitive cone photoreceptor cells in the retina. Each opsin binds to retinaldehyde, a molecule derived from vitamin A, and tunes it to respond to specific wavelengths of light. While all three opsins contain retinaldehyde, they bind to it differently, enabling the detection of different light wavelengths.
Key Findings
The study revealed structural differences in how the red, green, and blue cone opsins respond to light. According to Professor Lamb, the results show "fundamental differences between the cone opsins when they enter their active state after being hit with light."
"Red and green opsins appear to use different placement of chemical electronic charges around the retinaldehyde molecule."
This may explain their faster shut-off time compared to the blue opsin and rod pigment. These fast-switching properties are thought to aid in the perception of sharp detail and color in motion during daylight.
Significance
The rod pigment structure for vision in dim light was solved decades ago, while the structures of cone opsins for color vision had remained elusive. Understanding these molecular structures may help explain how vision disorders, such as cone dystrophies and altered color vision, arise at the molecular level.