In mammals, the bitter receptors are encoded by the bitter taste receptor gene (T2R) family, and they are seven transmembrane G protein coupled receptors (GPCR). Bitter taste is an effective defense mechanism that can avoid animals eating toxic substance since most of them are bitter. Bitter taste receptor gene 16 (T2R16) is a member of the bitter taste receptor gene family, which is the first identified receptor can be activated by natural bitterness substances. Research shows that T2R16 in human is under positive selection. And the function of T2R16 receptors have different degree of differentiation in primates, with human, chimpanzees, langur and macaques T2R16 receptors can recognize their corresponding ligands to different extent, however, the marmoset cannot recognize these bitter taste receptors ligands. These results implies that T2R16 may under adaptive evolution in the course of primate evolution, contradict with previously hypothesis that smell, taste and hearing abilities in primates were gradually degraded. Our main research focus is the evolution and function of the primate T2R16 receptors, tries to reveal whether the gene is under adaptive evolution in primates, deepen our understanding of evolution of bitter taste receptors in primates. Based on the functional analysis of T2R16 receptors in 8 primate species and 4 common ancestors (Hominoidea, Catarrhini, Platyrrhini and Simiiformes), combined with the evolution analysis of them in 24 primates, at least three adaptive evolutionary events were identified during primate evolution. These adaptive evolutionary events happened at the common ancestor of Simiiformes, common ancestor of Catarrhini and the human population. In this study, for the first time we revealed that T2R16 are under adaptive evolution in primates from one-to-one orthologous gene level. In order to further reveal the T2R16 molecular mechanisms of adaptive evolution, we firstly identify the conservative amino acid at the Simiiformes common ancestor and Catarrhini common ancestor through sequence comparison, which are 13 and 5 respectively. We then discovered that mutants at amino acids T82K I211M V239M significantly reduce the bitter substances detection ability of T2R16 receptors. This result indicates that at common ancestor of narrow nasal monkey the bitter detection ability may be increased due to the mutation of three amino acids, K82T M211I and M239V. This study has shed light on the ideas and methods of the T2R16 adaptive evolution analysis in primates.
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