Siegel N, Haug A
Biochim Biophys Acta. 1983 Apr 14;744(1):36-45. doi: 10.1016/0167-4838(83)90337-0.
The interaction of aluminum ions with bovine brain calmodulin has been examined by fluorescence spectroscopy, circular dichroic spectrophotometry and equilibrium dialysis, and by the calmodulin-dependent activation of 3',5'-cyclic nucleotide phosphodiesterase. These experiments show that aluminum binds stoichiometrically and cooperatively to calmodulin. Binding of aluminum at a molar ratio of 2:1 to calmodulin suffices to induce a major structural change. Estimates from spectroscopic data indicate that the binding affinity for the first mol of aluminum bound to the protein is about one order of magnitude stronger than that of calcium to its comparable site. These estimates agree with a dissociation constant of 0.4 microM derived from equilibrium dialysis experiments. Interaction of aluminum with calmodulin induces a helix-coil transition and enhances the hydrophobic surface area much more than calcium does. A molar ratio of 4:1 for [aluminum]/[calmodulin] is sufficient to block completely the activity of the calcium-calmodulin-dependent phosphodiesterase. Highly hydrated aluminum ions apparently promote solvent-rich, disordered polypeptide regions in calmodulin which, in turn, profoundly influence the protein's flexibility.
通过荧光光谱法、圆二色分光光度法和平衡透析法，并借助钙调蛋白依赖性3',5'-环磷酸二酯酶的激活，对铝离子与牛脑钙调蛋白的相互作用进行了研究。这些实验表明，铝以化学计量比且协同方式与钙调蛋白结合。铝与钙调蛋白以2:1的摩尔比结合足以引发主要的结构变化。光谱数据估计表明，与蛋白质结合的第一摩尔铝的结合亲和力比钙与其可比位点的结合亲和力强约一个数量级。这些估计值与平衡透析实验得出的0.4微摩尔解离常数相符。铝与钙调蛋白的相互作用诱导了螺旋-卷曲转变，并且比钙更能增加疏水表面积。铝与钙调蛋白的摩尔比为4:1足以完全阻断钙-钙调蛋白依赖性磷酸二酯酶的活性。高度水合的铝离子显然促进了钙调蛋白中富含溶剂的无序多肽区域，这反过来又深刻影响了蛋白质的柔韧性。
