Ogata C M, Gordon P F, de Vos A M, Kim S H
Howard Hughes Medical Institute, Department of Biochemistry and Molecular Biophysics Columbia University, New York, NY 10032.
J Mol Biol. 1992 Dec 5;228(3):893-908. doi: 10.1016/0022-2836(92)90873-i.
The crystal structure of thaumatin I, a potently sweet protein isolated from the fruits of the West African shrub, Thaumatococcus danielli Benth, has been refined at a resolution better than 1.65 A using a combination of energy minimization and stereochemically restrained least-squares methods. The final model consists of all 207 amino acids, 28 alternate amino acid conformers and 236 waters, with a crystallographic R-factor of 0.145 for 19,877 reflections having F > 4 sigma F between 10.0 A and 1.65 A (R = 0.167 for all 24,022 reflections). The model has good stereochemistry, with root-mean-square deviations from ideal values for bond and angle distances of 0.014 A and 0.029 A, respectively. The estimated root-mean-square co-ordinate error is 0.15 A. The current model confirms the previously reported 3.1 A C alpha trace in both main chain connectivity and disulfide topology, including two disulfide bonds, that differed from the earlier reported biochemical determination. The structure contains three domains. The core of the molecule consists of an eleven-stranded, flattened beta-sandwich folded into two Greek key motifs. All beta-strands in this sandwich are antiparallel except the parallel N-terminal and the C-terminal strands. The average hydrogen bond length in this sandwich is 2.89 A, with an angle of 155.1 degrees. Two beta-bulges are found in one of the sheets. The second domain consists of two beta-strands forming a beta-ribbon and connected by an omega-loop, and contains a proline residue in cis conformation. This structural motif folds back against the main sandwich to form a smaller sandwich-like structure. The third domain is a disulfide-rich region stretching away from the sandwich portion of the molecule. It contains one alpha-helix and three short helical fragments. Two of the helical segments are connected by an unusually sharp turn, stabilized by a disulfide bridge. One of the three disulfide bonds in this domain takes on two conformations.
奇异果甜蛋白I是从西非灌木植物丹尼氏奇异果（Thaumatococcus danielli Benth）果实中分离出的一种高效甜味蛋白，其晶体结构已通过能量最小化和立体化学约束最小二乘法相结合的方法，在分辨率优于1.65 Å的条件下进行了优化。最终模型包含所有207个氨基酸、28个交替的氨基酸构象异构体和236个水分子，对于19,877个在10.0 Å至1.65 Å之间F > 4σF的反射，晶体学R因子为0.145（对于所有24,022个反射，R = 0.167）。该模型具有良好的立体化学性质，键长和角度距离与理想值的均方根偏差分别为0.014 Å和0.029 Å。估计的坐标均方根误差为0.15 Å。当前模型在主链连接性和二硫键拓扑结构方面均证实了先前报道的3.1 Å Cα轨迹，包括两个二硫键，这与早期报道的生化测定结果不同。该结构包含三个结构域。分子核心由一个十一条链的扁平β-折叠片层组成，折叠成两个希腊钥匙基序。除了平行的N端和C端链外，这个折叠片中的所有β链都是反平行的。这个折叠片中的平均氢键长度为2.89 Å，角度为155.1度。在其中一个片层中发现了两个β-凸起。第二个结构域由两条形成β- ribbon并通过一个ω-环连接的β链组成，并且包含一个顺式构象的脯氨酸残基。这个结构基序向后折叠在主折叠片上，形成一个较小的类似折叠片的结构。第三个结构域是一个富含二硫键的区域，从分子的折叠片部分延伸出去。它包含一个α-螺旋和三个短螺旋片段。其中两个螺旋片段通过一个异常尖锐的转角连接，由一个二硫键稳定。这个结构域中的三个二硫键之一呈现两种构象。
