This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Our sense of taste is critical for survival, alerting us to substances that provide vital nutrients and those that might poison us. Now, a team led by researchers from the University of Osaka has discovered how one such taste receptor in pufferfish can detect a surprisingly wide range of flavors at once.
Their study is published in the Proceedings of the National Academy of Sciences. In many vertebrates, taste receptor type 1 (TAS1R) is the protein family responsible for detecting macronutrients and preferred tastes. Taste receptor genes across most vertebrate species are surprisingly consistent, designed to detect amino acids, sugars or nucleotides, although which ones they detect varies.
However, the structural basis for recognizing different chemicals and their specificity in TAS1Rs, particularly the umami receptor family, remains largely unknown because of difficulties in sample preparation. The research team determined, for the first time, the 3D crystal structure of pufferfish Tas1r1/Tas1r3, a macromolecule that is part of the TAS1R1 and TAS1R3B group of proteins and acts in a similar way to the human umami receptor, TAS1R1. The pufferfish receptor was found to respond to a much wider range of amino acids than the human umami receptor.
Moreover, unlike in humans, pufferfish receptors demonstrate rare stereochemical flexibility, binding to both savory L- and sweet D-amino acid variants. "We believe that the pufferfish's diet drives this molecular evolution," says senior author Atsuko Yamashita. "They eat a lot of mollusks and crustaceans, which contain high amounts of D-amino acids.
Generally, TAS1Rs are considered to discriminate between L- and D-amino acids and sense only one of them. The ability to taste both forms may help the fish detect a wider range of savory amino acids in their foods." The team identified for the first time the molecular structure and interactions that allow the receptor to bind to both types of amino acids, broadening taste detection in pufferfish. Normally, each taste receptor works like a clamp that closes around a target amino acid to switch on a taste signal.
The wrong amino acid prevents the molecular clamp from closing, blocking the signal. The team found extra internal connections—described as molecular "latches"—in the pufferfish receptor that hold the clamp shut even when the molecular fit is imperfect. "Normally, a receptor is unable to bind to a molecule that is the wrong shape," Yamashita explains.
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