title: Tuning properties of avian and frog bitter taste receptors dynamically fit gene repertoire sizes.
abstract: Bitter taste perception in vertebrates relies on a variable number of bitter taste receptor (Tas2r) genes, ranging from only three functional genes in chicken to as many as approximately 50 in frogs. Humans possess a medium-sized Tas2r repertoire encoding three broadly and several narrowly tuned receptors plus receptors with intermediate tuning properties. Such tuning information is not available for bitter taste receptors of other vertebrate species. In particular it is not known, whether a small Tas2r repertoire may be compensated for by broad tuning of these receptors, and on the other side, whether a large repertoire might entail a preponderance of narrowly tuned receptors. To elucidate this question, we cloned all three chicken Tas2rs, the two turkey Tas2rs, three zebra finch Tas2rs, and six Tas2rs of the Western clawed frog representative of major branches of the phylogenetic tree, and screened them with 46 different bitter compounds. All chicken and turkey Tas2rs were broadly tuned, the zebra finch Tas2rs were narrowly tuned, and frog Tas2rs ranged from broadly to narrowly tuned receptors. We conclude that a low number of functional Tas2r genes does not imply a reduced importance of bitter taste per se, as it can be compensated by large tuning width. A high number of functional Tas2r genes appears to allow the evolution of specialized receptors, possibly for toxins with species-specific relevance. In sum, we show that variability in tuning breadth, overlapping agonist profiles, and staggered effective agonist concentration ranges are shared features of human and other vertebrate Tas2rs.
authors.affiliation: Department of Molecular Genetics, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany behrens@dife.de.
authors.forename: Maik
authors.initials: M
authors.lastname: Behrens
authors.affiliation: Institute of Genetics, University at Cologne, Cologne, Germany.
authors.forename: Sigrun I
authors.initials: SI
authors.lastname: Korsching
authors.affiliation: Department of Molecular Genetics, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Meyerhof
mesh_terms: D029845:Amphibian Proteins / Q000819:agonists / Q000235:genetics* / Q000502:physiology; D000818:Animals; D001001:Anura / Q000235:genetics; D030161:Avian Proteins / Q000819:agonists / Q000235:genetics* / Q000502:physiology; D001717:Birds / Q000235:genetics; D019143:Evolution, Molecular; D057809:HEK293 Cells; D006801:Humans; D009665:Noscapine / Q000494:pharmacology; D010802:Phylogeny; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000819:agonists / Q000235:genetics* / Q000502:physiology; D015398:Signal Transduction; D013650:Taste Buds
chemical_list: D029845:Amphibian Proteins; D030161:Avian Proteins; D009665:Noscapine; D000644:Quaternary Ammonium Compounds; D011956:Receptors, Cell Surface; C043414:denatonium
keywords: G protein-coupled receptor; bitter taste receptor; evolution; heterologous expression