Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, USA.
J Phys Chem B. 2009 Nov 12;113(45):15083-9. doi: 10.1021/jp9051775.
Isothermal titration calorimetry (ITC) was used to determine the thermodynamics of protein binding to the nanoplates of alpha-Zr(HPO4)2.H2O (alpha-ZrP). The binding constants (K(b)) and DeltaG, DeltaH, and DeltaS have been evaluated for a small set of proteins, and K(b) values are in the range of 2-760 x 10(5) M(-1). The binding of positively charged proteins to the negatively charged alpha-ZrP was endothermic, while the binding of negatively charged proteins was exothermic, and these are contrary to expectations based on a simple electrostatic model. The binding enthalpies of the proteins varied over a range of -24 to +25 kcal/mol, and these correlated roughly with the net charge on the protein (R2 = 0.964) but not with other properties such as the number of basic residues, polar residues, isoelectric point, surface area, or molecular mass. Linear fits to the enthalpy plots indicated that each charge on the protein contributes 1.18 kcal/mol toward the binding enthalpy. Binding entropies of positively charged proteins were favorable (>0) while the binding entropies of negatively charged proteins were unfavorable (<0). The DeltaS values varied over a range of -51 to +98 cal/mol x K, and these correlated very well with the net charge on the protein (R2 = 0.999), but DeltaS is in the opposite direction of DeltaH. The binding or release of cations to/from the protein-solid interface can account for these observations. There was no correlation between the binding free energy (DeltaG(obs)) and any specific molecular properties, but it is likely to be a sum of several opposing interactions of large magnitudes. For the first time, the binding enthalpies and entropies are connected to specific molecular properties. The model suggests that the thermodynamic parameters can be controlled by choosing appropriate cations or by adjusting the net charge on the protein. We hope that physical insights such as these will be useful in understanding the complex behavior of proteins at biological interfaces.
使用等温热滴定法（ITC）来确定蛋白质与α-Zr(HPO4)2.H2O（α-ZrP）纳米板结合的热力学。已经评估了一小部分蛋白质的结合常数（K(b)）和ΔG、ΔH 和ΔS，K(b) 值的范围为 2-760×10(5) M(-1)。带正电荷的蛋白质与带负电荷的α-ZrP 的结合是吸热的，而带负电荷的蛋白质的结合是放热的，这与基于简单静电模型的预期相反。蛋白质的结合焓在-24 到+25 kcal/mol 的范围内变化，这些与蛋白质的净电荷大致相关（R2 = 0.964），但与其他性质如碱性残基数、极性残基数、等电点、表面积或分子量无关。对焓图的线性拟合表明，蛋白质上的每个电荷对结合焓的贡献为 1.18 kcal/mol。带正电荷的蛋白质的结合熵是有利的（>0），而带负电荷的蛋白质的结合熵是不利的（<0）。ΔS 值在-51 到+98 cal/mol x K 的范围内变化，与蛋白质的净电荷相关性非常好（R2 = 0.999），但ΔS 与ΔH 相反。蛋白质-固体界面上的阳离子的结合或释放可以解释这些观察结果。结合自由能（ΔG(obs)）与任何特定的分子性质之间没有相关性，但它可能是几个具有较大幅度的相反相互作用的总和。首次将结合焓和熵与特定的分子性质联系起来。该模型表明，热力学参数可以通过选择适当的阳离子或通过调整蛋白质的净电荷来控制。我们希望这些物理见解能够有助于理解蛋白质在生物界面的复杂行为。
