The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

Examining the co-evolution of primates and angiosperms: Brazzein sweet proteins and gorilla taste receptors


1Department of Anthropology, Yale University, 2Smithsonian Tropical Research Institute, Panamá, 3Department of Ecology and Evolutionary Biology, Yale University, 4Department of Zoology, Cambridge University, 5Department of Anthropology, The George Washington University

March 28, 2015 , Gateway Ballroom 2/3/4/5 Add to calendar

In mammals, G protein-coupled receptors on the tongue facilitate the perception of sweet taste. Although sweet taste normally functions to signal high energy content, several plants produce low-calorie proteins that also bind to sweet taste receptors, likely as a strategy to ‘trick’ animals into eating these low-energy fruits and dispersing the seeds. For example, brazzein, a protein produced by the West African plant Pentadiplandra brazzeana, binds to human sweet taste receptors, mimicking the taste of sugar. However, variation in the genes T1R2 and T1R3, which encode the sweet taste receptors, contributes to variation in the ability to taste various sweet molecules. Mice, for instance, exhibit several amino acid substitutions in the cysteine-rich region of T1R3 that prevent brazzein binding. We examined TIR3 sequence variation in primates and found that western gorillas (Gorilla gorilla gorilla) possess amino acid substitutions at three of the same amino acid positions, suggesting that they also do not taste sweet proteins as sweet. Because the distribution of western gorillas overlaps with that of Pentadiplandra brazzeana, evolution of T1R3 on the western gorilla lineage may have offered a way to avoid the plant’s false signal of energy content. To see whether eastern gorillas, which purportedly do not come into contact with brazzein, likely taste the protein as sweet, we also sequenced the relevant region of T1R3 in multiple eastern lowland gorillas (Gorilla beringei graueri). We found that the gorilla sequences are identical, suggesting that these changes in T1R3 occurred before the divergence between gorilla species.