Crystal structure of the sweet-tasting protein thaumatin II at 1.27 Å

Thaumatin, an intensely sweet-tasting protein, elicits a sweet taste sensation at 50 nM. Here the X-ray crystallographic structure of one of its variants, thaumatin II, was determined at a resolution of 1.27 Å. Overall structure of thaumatin II is similar to thaumatin I, but a slight shift of the Cα atom of G96 in thaumatin II was observed. Furthermore, the side chain of residue 67 in thaumatin II is highly disordered. Since residue 67 is one of two residues critical to the sweetness of thaumatin, the present results suggested that the critical positive charges at positions 67 and 82 are disordered and the flexibility and fluctuation of these side chains would be suitable for interaction of thaumatin molecules with sweet receptors.

► X-ray crystallographic structure of sweet-tasting protein, thaumatin II, was determined at a resolution of 1.27 Å. ► The overall structure of thaumatin II is similar to that of thaumatin I, but a slight shift of the Cα atom of G96 in thaumatin II was observed. ► The side chain of two critical residues, 67 and 82, for sweetness was modeled in two alternative conformations. ► The flexibility and fluctuation of side chains at 67 and 82 seems to be suitable for interaction of thaumatin molecules with sweet receptors.