Elucidation of the structure-function relationships in sweet-tasting proteins by x-ray analysis at atomic resolution

重组索马甜I的晶体结构被确定为1.1 A（PDB：3AL 7）的分辨率。其变体之一索马甜II的晶体结构以1.27 A（PDB：3AOK）的分辨率测定。结果表明，这些侧链的临界正电荷是无序的，这些侧链的灵活性和波动性将适合于与甜味受体的相互作用。以1.0 A的分辨率测定重组索马甜在pH 8.0下的原子结构（PDB：3VJQ）。结果表明，一些赖氨酸残基的迁移率显著增加，这可以促进与通过在高于7.0的pH下加热消除二硫键而产生的游离巯基残基的反应。制备了索马甜的各种突变体，并使用表达人甜味受体的HEK 293细胞通过基于细胞的测定定量评价了它们的甜味。构建了嵌合的人-鼠甜味受体，并研究了它们对甜味剂的反应.结果表明，人T1 R3的富含半胱氨酸的结构域对于对索马甜的应答是重要的。

The crystal structure of a recombinant thaumatin I was determined to a resolution of 1.1 A (PDB:3AL7). The crystallographic structure of one of its variants, thaumatin II, was determined at a resolution of 1.27 A (PDB:3AOK). The results showed the critical positive charges are disordered and the flexibility and fluctuation of these side chains would be suitable for interaction with sweet receptors. The atomic structure of a recombinant thaumatin at pH 8.0 was determined at a resolution of 1.0 A (PDB:3VJQ). The results suggested a striking increase in the mobility of some lysine residues, which could facilitate a reaction with a free sulfhydryl residue produced via the β-elimination of disulfide bonds by heating at a pH above 7.0. Various mutants of thaumatin were prepared and their sweetness were quantitatively evaluated by cell-based assays using HEK293 cells expressing human sweet receptors. Chimeric human- mouse sweet receptors were constructed and their responses to sweeteners were investigated. The results showed the cysteine-rich domain of human T1R3 is important for the response to thaumatin.