More than thirty years ago, I proposed a theory about sweet and bitter
molecules’ recognition by protein helical structures. Unfortunately the papers
could not go to public platform until now. The sweet and bitter taste theory is
updated and presented in separated papers1,2. The sweet taste theory conveys
that sweet molecules are recognized by receptor protein helical structures and
the recognition process is a dynamic action, in which the sweet receptor protein
helix has a torsion-spring-like oscillation between helical structures of 3.6 and 3
amino acids per turn. To help this kind of oscillation, there are two kinds of
hydrogen donor and hydrogen acceptor DH-B entities for both receptor and
sweet molecules: H-bond or non-H-bond. The distances between DH and B
could be up to ~ 8.5 Å. The receptor H-bond type DH-B entities are the NH-O
pairs forming H-bonds in protein helices; the receptor non-H-bond type DH-B
entities are the ones from two pairs of NH-Os forming H-bonds which are about
one turn away. To facilitate this kind of movement, the interaction of DH-Bs of a
sweet molecule with those of sweet receptor, through a pair of complementary
hydrogen bonds, must have hydrogen bond complementarities, which means Hbond
type of ligands’ DH-Bs reacts on non-H-bond type of receptor’s O-NHs, and
vice versa. As the oscillation may have different extent, it translates to sweet
intensity. As recognition sites are only associated with a small fraction – helix
structure of whole sweet receptor, multiple binding sites or multiple receptors are
well expected.