Even if we take our senses for granted, they can still hide surprises. Eastern chefs discovered first, at the beginning of the century, that sweet, bitter, salty and sour are not the only tastes that our buds can perceive. We can enjoy a fifth side of flavour in our plates, the “savouriness”. The world now refers to it more and more as umami, the name given by its japanese discoverer. It comes especially from glutamate; and thus, from proteins-rich food: meats and their broths, algae, cheese, soy and mushrooms. Umami is the secret of oriental cuisine and its controversial condiment, MSG – monosodium glutamate – that gives our palates a hearty feeling.
A century after its first official description by professor Ikeda, Umami was still keeping secrets from the culinary scientist. An in it these lied one of its most wonderful potential for the adventurous cook : its taste can be multiplied exponentially by a variety of ingredients. Notably inoside and guanoside monophosphate, as well as certain sweeteners greatly enhance its flavour.
The umami taste receptor, mGluR4, presents an extensive similarity with the sweet taste receptor. Both are G-coupled heterodimeric protein complex and share a ligand-binding domain, TIR3, while the umami taste receptor possess a unique glutamate-binding domain, TIR1. The association of glutamate to TIR1 elicit the signal that our brain interprets as a hearty flavour. Interestingly, when conserved residues between TIR1 and TIR2 are mutated, the synergetic effect of IMP and GMP is lost. Using molecular modelling, chemists showed that the mystery resides in the phosphate group of the molecules. They allow IMP and GMP to bind near the entrance of the crevice to positively charged residues, stabilizing a closed conformation around the glutamate and thus stimulating the production of the signal to the brain.
A wonderful examples of molecules working together for our enjoyment!
For further reading :
A century after its first official description by professor Ikeda, Umami was still keeping secrets from the culinary scientist. An in it these lied one of its most wonderful potential for the adventurous cook : its taste can be multiplied exponentially by a variety of ingredients. Notably inoside and guanoside monophosphate, as well as certain sweeteners greatly enhance its flavour.
The umami taste receptor, mGluR4, presents an extensive similarity with the sweet taste receptor. Both are G-coupled heterodimeric protein complex and share a ligand-binding domain, TIR3, while the umami taste receptor possess a unique glutamate-binding domain, TIR1. The association of glutamate to TIR1 elicit the signal that our brain interprets as a hearty flavour. Interestingly, when conserved residues between TIR1 and TIR2 are mutated, the synergetic effect of IMP and GMP is lost. Using molecular modelling, chemists showed that the mystery resides in the phosphate group of the molecules. They allow IMP and GMP to bind near the entrance of the crevice to positively charged residues, stabilizing a closed conformation around the glutamate and thus stimulating the production of the signal to the brain.
A wonderful examples of molecules working together for our enjoyment!
For further reading :
Zhang F. et al. 2008 Molecular mechanism for the umami taste synergism Proc. Natl. Ac. Sci. 105(52), 20930-4
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