Bitter Taste Sensitivity in Humans and Chimpanzees

Abstract

Bitter taste receptors (TAS2Rs) serve an important function during evolution. They are designed to detect toxic plant metabolites before ingestion. With respect to bitter taste receptors the genetic repertoire of animal species is highly diverse reflecting the species differences in their metabolic requirements, the variety of habitats and evolutionary history. Over the recent years, an incredible amount of data on human bitter taste receptor pharmacology, biochemistry and structural features has accumulated. It became apparent that TAS2R gene expression is not restricted to the oral cavity, but includes several nongustatory tissues, thus expanding the presumed roles of TAS2Rs. By comparing the bitter taste receptor genes of humans with our closest relative, the chimpanzee, we learn about some of the evolutionary forces that shaped the development of modern human beings. This article discusses the current knowledge on bitter taste physiology, TAS2R function and evolutionary conservation of human and chimpanzee TAS2R genes.

Key Concepts:

  • Taste physiology and hedonics of bitter taste appear similar in humans and chimpanzees.

  • Human bitter taste receptors can be grouped into generalists and specialists depending on their tuning breadth.

  • Similar to the human situation, bitter tasting abilities of the chimpanzee are in some instances individual.

  • Dynamic evolution of human and chimpanzee TAS2R genes is earmarked by regional diversification.

  • The rate of TAS2R gene pseudogenisation indicates relaxed evolutionary constraints in the primate lineage.

Keywords: bitter taste receptor genes; TAS2R; taste; dynamic evolution; food selection

Figure 1.

Bitter taste signal transduction casacade. Bitter taste receptors possess seven transmembrane helices (I–VII). After agonist activation, the heterotrimeric G protein consisting of Gα‐gustducin (α)/β3 or β1 (β)/γ13 (γ) dissociates. The dimeric β/γ subunits activate phospholipase Cβ2 (PLCβ2), which in turn produces inositol trisphosphate (IP3). IP3 triggers via the type‐III IP3 receptor the release of calcium from intracellular stores leading to the opening of the transient receptor potential channel M5 (TRPM5) resulting in the generation of action potentials.

Figure 2.

Family of human and chimpanzee TAS2R genes. The phylogenetic tree shows the relationships among the 36 human and chimpanzee orthologous TAS2R gene nucleotide sequences. For the construction of the phylogentic tree the complementary deoxyribonucleic acid (cDNA) sequences of human and chimpanzee TAS2Rs were aligned using the pileup function of the Genetics Computer Group, Inc.‐program. The 25 TAS2Rs that are functional in humans and chimpanzees are printed in bold. The old numbers of recently renamed human TAS2Rs are given in parenthesis. The three TAS2R genes which are pseudogenes in humans but putatively functional in chimpanzees are marked by asterisks. Synonymous names are boxed in grey (1, Go et al., ; 2, Shi et al., ).

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Yarmolinsky DA, Zuker CS and Ryba NJ (2009) Common sense about taste: from mammals to insects. Cell 139(2): 234–244.

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Behrens, Maik, and Meyerhof, Wolfgang(Jun 2013) Bitter Taste Sensitivity in Humans and Chimpanzees. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0020778.pub2]