Pérez-Hernández Gerardo, García-Hernández Enrique, Zubillaga Rafael A, de Gómez-Puyou Marietta Tuena
Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico.
Arch Biochem Biophys. 2002 Dec 15;408(2):177-83. doi: 10.1016/s0003-9861(02)00577-5.
The energetics of binding of MgADP to the isolated beta subunit of F(1)-ATPase from thermophilic Bacillus (Tbeta) was characterized by high-precision isothermal titration calorimetry. The reaction was enthalpically driven, with a DeltaCp of -36cal(molK)(-1). To gain insight into the molecular basis of this small DeltaCp, we analyzed the changes in accessible surface areas (DeltaASA) between the structures of empty and MgADP-filled beta subunits, extracted from the crystal structure of bovine heart F(1). Consistent with the experimental DeltaCp, the DeltaASA was small (-775A(2)). We used a reported surface area model developed for protein reactions to calculate DeltaCp and DeltaH from DeltaASA, obtaining good agreement with the experimental values. Conversely, using the same model, a DeltaASA of -770A(2) was estimated from experimental DeltaCp and DeltaH for the Tbeta-MgADP complex. Our structural-energetic study indicates that on MgADP binding the isolated Tbeta subunit exhibits intrinsic structural changes similar to those observed in F(1).
通过高精度等温滴定量热法对嗜热芽孢杆菌F(1)-ATP酶分离出的β亚基（Tβ）与MgADP的结合能进行了表征。该反应由焓驱动，ΔCp为-36cal/(mol·K)。为深入了解这种小ΔCp的分子基础，我们分析了从牛心F(1)晶体结构中提取的空β亚基和填充MgADP的β亚基结构之间可及表面积（ΔASA）的变化。与实验测得的ΔCp一致，ΔASA很小（-775Ų）。我们使用一个为蛋白质反应开发的已报道表面积模型，根据ΔASA计算ΔCp和ΔH，所得结果与实验值吻合良好。相反，使用相同模型，从Tβ-MgADP复合物的实验ΔCp和ΔH估计出ΔASA为-770Ų。我们的结构能量研究表明，MgADP结合时，分离出的Tβ亚基表现出与F(1)中观察到的类似的内在结构变化。
