Marked increase in PROP taste responsiveness following oral supplementation with selected salivary proteins or their related free amino acids.

Melania Melis,Massimo Castagnola,Irene Messana,Beverly J Tepper,Tiziana Cabras,Maria Carla Aragoni,Claudia Caltagirone,Massimiliano Arca,Roberto Crnjar,Iole Tomassini Barbarossa,Wolfgang Meyerhof

doi:10.1371/journal.pone.0059810

Melania Melis, Massimo Castagnola + Show 9 more

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https://doi.org/10.1371/journal.pone.0059810

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Abstract

The genetic predisposition to taste 6-n-propylthiouracil (PROP) varies among individuals and is associated with salivary levels of Ps-1 and II-2 peptides, belonging to the basic proline-rich protein family (bPRP). We evaluated the role of these proteins and free amino acids that selectively interact with the PROP molecule, in modulating bitter taste responsiveness. Subjects were classified by their PROP taster status based on ratings of perceived taste intensity for PROP and NaCl solutions. Quantitative and qualitative determinations of Ps-1 and II-2 proteins in unstimulated saliva were performed by HPLC-ESI-MS analysis. Subjects rated PROP bitterness after supplementation with Ps-1 and II-2, and two amino acids (L-Arg and L-Lys) whose interaction with PROP was demonstrated by 1H-NMR spectroscopy. ANOVA showed that salivary levels of II-2 and Ps-1 proteins were higher in unstimulated saliva of PROP super-tasters and medium tasters than in non-tasters. Supplementation of Ps-1 protein in individuals lacking it in saliva enhanced their PROP bitter taste responsiveness, and this effect was specific to the non-taster group.1H-NMR results showed that the interaction between PROP and L-Arg is stronger than that involving L-Lys, and taste experiments confirmed that oral supplementation with these two amino acids increased PROP bitterness intensity, more for L-Arg than for L-Lys. These data suggest that Ps-1 protein facilitates PROP bitter taste perception and identifies a role for free L-Arg and L-Lys in PROP tasting.

Highlights

The ability to detect bitterness may have evolved to protect human beings from ingesting bitter-tasting toxins from plants and the environment
We recently showed that PROP status is associated with basal levels of two salivary peptides belonging to the basic proline-rich protein family, namely Ps-1 and II-2, which are both encoded by the PRB1 gene [47]
Ps-1 or II-2 Oral Supplementation Figure 2 shows the distributions of the relative concentrations of the Ps-1 protein and II-2 peptide determined by HPLC-ESI-ITMS analysis in unstimulated saliva of PROP super-tasters, medium tasters and non-tasters

Summary

Introduction

The ability to detect bitterness may have evolved to protect human beings from ingesting bitter-tasting toxins from plants and the environment. Humans possess an array of ,25 bitter receptors that are capable sensing thousands of natural and synthetic compounds that impart bitter taste [1,2,3,4] Some of these receptors are generalists, activated by many, chemically-diverse compounds (broadly tuned), whereas others are specialists, responding to only a single or a few compounds with closely-related structures [5]. Genetic variability in taste sensitivity to thiourea derivatives, such as phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP), is one of the moststudied human traits [6]. Both PROP and PTC contain a thiourea functional group (SC(NHR)2), which is responsible for their bitter taste [7,8,9]. These variants do not function as broad-based genetic markers of chemosensory responsiveness as has been attributed to PROP phenotype

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