Genetics of Taste Sensitivity - Part 3: How to turn a PROP non-taster into a taster

In their ongoing exploration of PROP tasting ability, Tomassini-Barbarossa and colleagues from the University of Cagliari, Monserrato, Calabria, Italy, together with Beverly Tepper from Rutgers University in New Jersey, have discovered yet another determinant of the ability to taste the bitter chemical PROP.*

If you remember (see post of March 13), one of the determinants of the perceived intensity of PROP's bitterness is the number of fungiform taste papillae one has. Taste papillae number and shape depend on the presence of an active form of a protein called gustin in their saliva. People with one copy of the gene for the active protein are moderate tasters, provided that they also have an active gene for the PROP receptor TAS2R38. People with two copies of the active version of the gustin gene have an abundance of papillae, and PROP tastes extra bitter to them.

In the work presented in the paper cited below, the authors show how to turn a non-taster of PROP into a taster, despite having two copies of the mutated non-tasting gene! 

People who inherited two copies (one from each parent) of the non-taster form of the TAS2R38 cannot taste PROP by itself. But when it is mixed in solution with the amino acid L-arginine, they can taste it. Somehow, the interaction of L-arginine with the PROP molecule makes it able to attach to mutated TAS2R38 receptors and activate them. 

Apparently, non-tasters tend to have little free L-arginine in their saliva, so they normally don't taste PROP. By contrast, highly sensitive tasters of PROP tend to have a large amount of L-arginine, which greatly enhances their ability to taste the chemical. 

Interestingly, highly sensitive tasters of PROP also tend to find caffeine very bitter, while non-tasters do not, even though caffeine binds to five different receptors. L-arginine can make a caffeine solution more bitter for these people who don't find plain caffeine to be particularly so. 

Just to think what this means for pairing...more to come!

* Melania Melis, Massimiliano Arca, Maria Carla Aragoni, Tiziana Cabras, Claudia Caltagirone, Massimo Castagnola, Roberto Crnjar, Irene Messana, Beverly J. Tepper, and  Iole Tomassini Barbarossa. Dose-Dependent Effects of L-Arginine on PROP Bitterness Intensity and Latency and Characteristics of the Chemical Interaction between PROP and L-Arginine. PLoS One. 2015; 10(6): e0131104. Published online 2015 Jun 23. doi:  10.1371/journal.pone.0131104