Plants and Animals

Worms Can Taste Sunlight

Eyeless nematode worms are able to detect sunlight using their taste receptors, new research has found. Amazingly, these receptors – known as LITE-1 receptors – are between 10 and 100 times more light sensitive than all other known photoreceptors in the animal kingdom, and could therefore help scientists to develop new super-strength sunscreens, among other things.

Two different types of photoreceptors – known as opsins and cryptochromes – exist in animals. Both of these are made up of a structural “host protein” and a light-sensitive component called a chromophore. Nematodes, however, lack photoreceptors, yet still manage to detect and respond to light, deliberately moving away from bright flashes and burying themselves in darkness.

Using spectrophotometric analysis, researchers discovered that LITE-1, which is found among nematodes’ taste receptors, absorbs two types of ultraviolet light, known as UV-A and UV-B. However, unlike animal photoreceptors, LITE-1 doesn’t react with light particles – or photons – in order to generate a signal, but simply absorbs them directly.

“LITE-1 is unusual in that it is extremely efficient at absorbing both UV-A and UV-B light – 10 to 100 times greater than the two other types found in the animal kingdom,” explained study co-author Shawn Xu in a statement.

Publishing their work in the journal Cell, the researchers claim that this ability to absorb the Sun’s ultraviolet light could make LITE-1 an excellent addition to commercial sunscreens, and might also be used to develop new types of artificial photoreceptors.

First, though, the team needed to figure out how LITE-1 works – so they decided to try and break it. Because animal photoreceptors consist of a protein and a chromophore, denaturing the protein component doesn’t cause them to stop functioning, as the light-sensitive ingredient remains intact. Yet when the researchers denatured LITE-1, it became completely inoperative, suggesting that it works in a completely different way to both opsins and cryptochromes.

Further investigation revealed that the light sensitivity of LITE-1 is caused by the presence of two amino acids called tryptophan residues. To confirm this, the team genetically modified some of the nematodes’ other taste receptors to include these compounds, and found that they too became responsive to sunlight.

If this can be repeated in other cells, such as those in the human eye, it might one day be possible to create new, super-sensitive photoreceptors that function in the same way as LITE-1.

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