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Appl. Chem. Vol. 74, No. 7, pp.
Pure and Applied Chemistry
Vol. 74, Issue 7
Structuretaste relationships of the sweet protein monellin*
Masanori Kohmura**, Toshimi Mizukoshi, Noriki Nio, Ei-ichiro Suzuki,
and Yasuo Ariyoshi
Central Research Laboratories, Ajinomoto Co., Inc.,
1-1 Suzuki-cho, Kawasaki-ku, Kawasaki, 210-8681 Japan
Abstract: Structuretaste relationship studies
were carried out by chemically synthesizing monellin and its analogs.
Replacement of the AspB7 by L-2-aminobutyric
acid, Gly and D-Asp resulted in complete loss
of sweetness. Replacement of IleB6 and IleB8 by
different amino acids resulted in a significant decrease of sweetness,
or complete loss of sweetness. Comparison of short- and long-range nuclear
Overhauser effects (NOEs) and chemical shifts between monellin and [AbuB7]monellin
showed no marked differences except for the region of the AspB7.
Thus, the complete loss of sweetness in [AbuB7]monellin is
caused by the lack of free b-carboxyl group
in the AspB7 and not by a result of major disruption in the
overall 3-dimensional structure. These results suggested that the free
b-carboxyl group of the AspB7
would possibly bind to the receptor site through ionic bonding and trigger
the sensation of intense sweet taste, and IleB6 and/or IleB8
would be involved in the hydrophobic interaction with the receptor site.
Selectively labeled monellin was synthesized by the solid-phase method
by incorporating 15N-labeled amino acids into 10 key residues
including AspB7. Relaxation analysis shows that AspB7
is the most flexible of these 10 residues. The flexibility of the active
site may be important for receptor binding.
* A special topic issue on the
science of sweeteners.
** Corresponding author.
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