St Charles R, Harrison R W, Bell G I, Pilkis S J, Weber I T
Department of Pharmacology, Jefferson Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
Diabetes. 1994 Jun;43(6):784-91. doi: 10.2337/diab.43.6.784.
Recent studies have shown that mutations in human beta-cell glucokinase that impair the activity of this key regulatory enzyme of glycolysis can cause early-onset non-insulin-dependent diabetes mellitus (NIDDM). The amino acid sequence of human glucokinase has 31% identity with yeast hexokinase, a related enzyme for which the crystal structure has been determined. This homology has allowed us to model the three-dimensional structure of human glucokinase by analogy to the crystal structure of yeast hexokinase B. This model of human glucokinase provides a basis for understanding the effects of mutations on its enzymatic activity. Residues in the active site and on the surface of the binding cleft for glucose are highly conserved in both enzymes. Regions far from the active site are predicted to differ in conformation, and 10 insertions or deletions that range in size from 1 to 7 residues are located on the protein surface between elements of secondary structure. The model structure suggests that human glucokinase binds glucose in a similar manner to yeast hexokinase. The glucose-binding site contains a conserved aspartic acid, two conserved glutamic acids, and two conserved asparagines that form hydrogen bond interactions with the hydroxyls of the glucose similar to those observed in other sugar-binding proteins. Mutation of residues in the predicted glucose-binding site has been found to greatly reduce enzymatic activity. This model will be useful for future structure/function studies of glucokinase.
最近的研究表明，人类β细胞葡萄糖激酶的突变会损害这种糖酵解关键调节酶的活性，从而导致早发性非胰岛素依赖型糖尿病（NIDDM）。人类葡萄糖激酶的氨基酸序列与酵母己糖激酶有31%的同源性，酵母己糖激酶是一种相关酶，其晶体结构已被确定。这种同源性使我们能够通过类比酵母己糖激酶B的晶体结构来模拟人类葡萄糖激酶的三维结构。这种人类葡萄糖激酶模型为理解突变对其酶活性的影响提供了基础。两种酶在活性位点和葡萄糖结合裂隙表面的残基高度保守。预计远离活性位点的区域在构象上会有所不同，在二级结构元件之间的蛋白质表面上有10个大小从1到7个残基不等的插入或缺失。模型结构表明，人类葡萄糖激酶与酵母己糖激酶结合葡萄糖的方式相似。葡萄糖结合位点包含一个保守的天冬氨酸、两个保守的谷氨酸和两个保守的天冬酰胺，它们与葡萄糖的羟基形成氢键相互作用，类似于在其他糖结合蛋白中观察到的情况。已发现预测的葡萄糖结合位点中的残基突变会大大降低酶活性。该模型将有助于未来对葡萄糖激酶的结构/功能研究。
