Kurimoto Eiji, Suzuki Maiko, Amemiya Eiko, Yamaguchi Yoshiki, Nirasawa Satoru, Shimba Nobuhisa, Xu Ningchun, Kashiwagi Tatsuki, Kawai Misako, Suzuki Ei-Ichiro, Kato Koichi
Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603.
Enzyme Laboratory, National Food Research Institute, 2-1-12 Kannondai, Tsukuba 305-8642, Ibaraki.
J Biol Chem. 2007 Nov 16;282(46):33252-33256. doi: 10.1074/jbc.C700174200. Epub 2007 Sep 25.
Curculin isolated from Curculigo latifolia, a plant grown in Malaysia, has an intriguing property of modifying sour taste into sweet taste. In addition to this taste-modifying activity, curculin itself elicits a sweet taste. Although these activities have been attributed to the heterodimeric isoform and not homodimers of curculin, the underlying mechanisms for the dual action of this protein have been largely unknown. To identify critical sites for these activities, we performed a mutational and structural study of recombinant curculin. Based on the comparison of crystal structures of curculin homo- and heterodimers, a series of mutants was designed and subjected to tasting assays. Mapping of amino acid residues on the three-dimensional structure according to their mutational effects revealed that the curculin heterodimer exhibits sweet-tasting and taste-modifying activities through its partially overlapping but distinct molecular surfaces. These findings suggest that the two activities of the curculin heterodimer are expressed through its two different modes of interactions with the T1R2-T1R3 heterodimeric sweet taste receptor.
从马来西亚生长的一种植物宽叶仙茅中分离出的仙茅蛋白具有一种将酸味转化为甜味的有趣特性。除了这种味觉修饰活性外，仙茅蛋白本身也能引发甜味。尽管这些活性归因于仙茅蛋白的异源二聚体异构体而非同源二聚体，但这种蛋白质双重作用的潜在机制在很大程度上尚不清楚。为了确定这些活性的关键位点，我们对重组仙茅蛋白进行了突变和结构研究。基于仙茅蛋白同源二聚体和异源二聚体晶体结构的比较，设计了一系列突变体并进行味觉测定。根据氨基酸残基的突变效应将其映射到三维结构上，结果表明仙茅蛋白异源二聚体通过其部分重叠但不同的分子表面表现出甜味和味觉修饰活性。这些发现表明，仙茅蛋白异源二聚体的两种活性是通过其与T1R2 - T1R3异源二聚体甜味受体的两种不同相互作用模式来表达的。
