But what causes the sensation of sourness, and why do we like it so much? USC scientists may have solved the first mystery: how sour tastes are sensed by animals.
Fruits and vegetables that taste sour are high in acids, including citric acid for lemons, tartaric acid for grapes and acetic acids in fermented foods like vinegar. It has been recognized for more than a century -- since the introduction of the pH meter -- that the low pH and high concentration of H+ ions in these foods generate a perception of sourness in humans. But how pH is sensed at the level of the tongue, and specifically what molecule constitutes the pH sensor, was not known.
Group - Emily - Liman - Professor - Sciences
A group led by Emily Liman, professor of biological sciences at the USC Dornsife College of Letters, Arts & Sciences, have reported in Current Biology that a sensor for pH on the tongue is the otopetrin 1 gene (Otop1). Otop1 is a member of a class of molecules called ion channels, which allow charged ions to cross cell membranes. In the case of Otop1, the charged ion carried across the membrane is H+, which is released into the mouth by acids.
Last year, Liman's team published research in Science that closed in on the sour-taste sensor. In that study, they used high-throughput sequencing methods made possible by advances in genomics to identify a list of roughly 40 previously uncharacterized genes that could encode a sour sensor. By studying the function of each gene, they whittled the list down to Otop1 because it was the only candidate that, when introduced into non-taste cells, gave them the ability to respond to acids.
USC - Scientists - OTOP1 - Protein - Otop1
While the USC scientists had identified OTOP1 -- the protein encoded by the Otop1 gene -- as forming a proton channel, they did not show that it...
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