Scientists have discovered a new class of taste buds. This is stated in a large study by a group of biologists from the University of California, a description of which was published in Phys.org.
A team of scientists determined that numerous opsin proteins, known for decades, which are the main compound of the visual pigment rhodopsin, also function as taste receptors.
In animals, there are many types of sensory proteins that respond to environmental stimuli. Some of them require a strong external stimulus to activate. For the first time, the additional functions of opsin became known back in 2011, when the same scientists discovered that such a protein allows the fruit fly Drosophila melanogaster to detect small temperature changes within a comfortable range. In a new study, scientists concluded that opsin molecules can also be used to detect fine chemical signals through a signal amplification process.
During the study, scientists suggested that flies choose between simple sugar and sugar with the addition of diluted aristolochic acid. Flies, of course, refused sugar with the addition of a bitter chemical and ate only pure sugar.
Scientists then grew fruit flies with mutations that prevented them from synthesizing various opsin proteins. They found that flies with defects in any of the three types of opsins could not detect low acid concentrations, so they ate both pure sugar and other substances.
However, such animals were still sensitive to a large amount of aristolochic acid. According to the study, a large amount of a bitter chemical directly activated a protein channel called TRPA1 – it passes calcium and sodium into cells, which leads to a bitter taste that animals avoid.
Researchers have shown that aristolochic acid-activated these opsins by binding to the body in the same way as the retina with rhodopsin. Just as rhodopsins are activated in very low light, which is used as an external stimulus, chemically activated opsins initiate a molecular cascade that amplifies weak signals. This allowed the flies to detect compound concentrations that would otherwise be insufficient to trigger a response in their sensory neurons.