In their quest to find “light-eating” proteins, cellular components that help plants and microbes harvest light from the sun, a team of scientists has stumbled upon the first new kind in nearly 50 years—at the bottom of the Sea of Galilee. The unexpected discovery could help researchers better understand how microbes sense light, and it could power new kinds of light-based research and data storage techniques.
Many organisms use light-sensitive proteins to gather the sun’s energy and help them survive. Some use chlorophyll to convert sunlight during photosynthesis and others use rhodopsins, proteins that bind to a form of vitamin A called retinal to capture light. The best known rhodopsin is embedded in the rod cells of our eyes, where it helps us see in the dark. But another form of rhodopsin helps small organisms, such as algae and bacteria, absorb light to make chemical energy.
Researchers were searching for the second type of rhodopsin when they collected DNA samples from the Sea of Galilee in Israel. They returned to their lab and screened the DNA for genes that coded for the light-reacting proteins. When they added retinal to Escherichia coli bacteria hosting the DNA, it turned purple—a sign that rhodopsins might be present (above). When they tested the DNA further, they discovered a completely new light-eating protein, a type of rhodopsin they named heliorhodopsin, the team reported last month in Nature.
Scientists don’t know much about how heliorhodopsin works. Its DNA is similar to the rhodopsin that creates chemical energy. But because it takes so long to finish its light-conversion cycle, the researchers suspect that—similar to the rhodopsin in our eyes—it is a light-sensing protein. What they know for sure: The new protein seems to be everywhere, in bacteria, algae, archaea, and even viruses in the soil and in every major body of water on Earth. This new protein family is even found in bacteria and other microorganisms that were never known to sense light until now.
The light-sensing protein could lead to applications in everything from data storage to optogenetics, which allows scientists to manipulate genetically modified nerve cells with light. But first, scientists must answer many questions about the protein’s fundamentals.