July 2002
Taste Receptor for Amino Acids Discovered
Scientists recently reported the discovery of a new taste receptor that recognizes
most of the 20 naturally occurring amino acids, leading them to speculate that
it evolved to help us select foods rich in these essential nutrients.
Published in Nature, the report is the latest in a series of articles
resulting from a five-year collaboration between investigators jointly led by
Dr. Nicholas Ryba at the NIDCR and Dr. Charles Zuker of the Howard Hughes Medical
Institute at the University of California, San Diego.
According to Ryba, "The amino acid receptor is related to the sweet taste
receptor that we identified and characterized last year: both are combinations
of a family of taste receptors referred to as TR1." They made this new
discovery by inserting mouse T1R genes into cells engineered to respond to and
report receptor activation. Surprisingly, the investigators found that different
combinations of the T1R receptors resulted in either a sweet taste receptor
or an amino acid taste receptor.
The scientists note that in mice, the same taste receptor recognizes nearly
all amino acids, but that the human receptor is much more specifically tuned
to recognize one in particular - glutamate.
Glutamate occurs naturally in certain foods, such as seafood, and is often
added to processed food as the flavor enhancer monosodium glutamate (MSG). It
has a unique flavor known as "umami," a Japanese word meaning delicious.
According to Ryba, "the human receptor is far more sensitive to glutamate
than other amino acids and is very likely to be a major receptor for the umami
taste."
There are benefits to deciphering the umami taste pathway, Ryba notes. He points
out that, while many of us associate the umami taste of MSG with processed or
snack foods, some researchers are using MSG to stimulate consumption of nutritious
foods by those with poor appetites, such as the elderly and people with diabetes.
Ryba concludes, "There remains a substantial amount of biology that we
still need to determine in order to understand the relationship between receptor
activity and taste perception." To answer these questions, the scientists
plan to use genetically engineered mice to study the effect of altering or deleting
the T1R taste receptors.
This research was reported in the March 14, 2002 issue of Nature.
--Georgeann Smale
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