Parfenyev A N, Salminen A, Baykov A A, Lahti R
Belozersky Institute of Physico-Chemical Biology and School of Chemistry, Lomonosov Moscow State University, Moscow, 119899, Russia.
Biochemistry (Mosc). 2000 Mar;65(3):388-92.
Three Gln-80 residues belonging to different subunits of homohexameric Escherichia coli pyrophosphatase are separated by only one water molecule to which they are hydrogen bonded. Substitution of Glu for Gln-80 stabilizes quaternary structure of the enzyme but has only a small effect on enzyme activity. The substitution stimulates Mg2+ binding and changes the appearance of the Mg2+ concentration dependence of the rate constant for the trimer --> hexamer transition. These data suggest that a new Mg2+ binding site is formed in the intersubunit contact region as a result of the substitution. Three-dimensional modeling of the mutated protein showed that a chelate complex might form involving two of the three Glu-80 residues.
属于同六聚体大肠杆菌焦磷酸酶不同亚基的三个谷氨酰胺-80残基仅被一个与之形成氢键的水分子隔开。用谷氨酸取代谷氨酰胺-80可稳定该酶的四级结构，但对酶活性仅有微小影响。这种取代刺激了镁离子结合，并改变了三聚体→六聚体转变速率常数对镁离子浓度依赖性的表现形式。这些数据表明，由于这种取代，在亚基间接触区域形成了一个新的镁离子结合位点。对突变蛋白的三维建模显示，可能形成一种螯合物，涉及三个谷氨酸-80残基中的两个。
