Kaneko R, Kitabatake N
Research Institute for Food Science, Kyoto University, Uji, Kyoto 611-0011, Japan.
Chem Senses. 2001 Feb;26(2):167-77. doi: 10.1093/chemse/26.2.167.
To clarify the structural basis for the sweetness of thaumatin I, lysine-modified derivatives and carboxyl-group-modified derivatives were prepared by chemical modification followed by chromatographic purification. The sweetness of derivatives was evaluated by sensory analysis. Phosphopyridoxylation of lysine residues Lys78, Lys97, Lys106, Lys137 and Lys187 markedly reduced sweetness. The intensity of sweetness was returned to that of native thaumatin by dephosphorylation of these phosphopyridoxylated lysine residues except Lys106. Pyridoxamine modification of the carboxyl group of Asp21, Glu42, Asp60, Asp129 or Ala207 (C-terminal) did not markedly change sweetness. Analysis by far-UV circular dichroism spectroscopy indicated that the secondary structure of all derivatives remained unchanged, suggesting that the loss of sweetness was not a result of major disruption in protein structure. The five lysine residues, modification of which affected sweetness, are separate and spread over a broad surface region on one side of the thaumatin I molecule. These lysine residues exist in thaumatin, but not in non-sweet thaumatin-like proteins, suggesting that these lysine residues are required for sweetness. These lysine residues may play an important role in sweetness through a multipoint interaction with a putative thaumatin receptor.
为阐明奇异果甜蛋白I甜味的结构基础，通过化学修饰和色谱纯化制备了赖氨酸修饰衍生物和羧基修饰衍生物。通过感官分析评估衍生物的甜度。赖氨酸残基Lys78、Lys97、Lys106、Lys137和Lys187的磷酸吡哆醛化显著降低了甜度。除Lys106外，这些磷酸吡哆醛化赖氨酸残基的去磷酸化使甜度强度恢复到天然奇异果甜蛋白的水平。对Asp21、Glu42、Asp60、Asp129或Ala207（C端）的羧基进行吡哆胺修饰并没有显著改变甜度。远紫外圆二色光谱分析表明，所有衍生物的二级结构保持不变，这表明甜度的丧失不是蛋白质结构发生重大破坏的结果。五个赖氨酸残基的修饰影响甜度，它们相互分离，分布在奇异果甜蛋白I分子一侧的广阔表面区域。这些赖氨酸残基存在于奇异果甜蛋白中，但不存在于非甜味的类奇异果甜蛋白中，这表明这些赖氨酸残基是产生甜味所必需的。这些赖氨酸残基可能通过与假定的奇异果甜蛋白受体的多点相互作用在甜味中发挥重要作用。
