ENERGETICS OF TARGET PEPTIDE RECOGNITION BY CALMODULIN: CALORIMETRIC STUDY

钙调蛋白是一种小蛋白，参与调节广泛的 细胞内突起的多样性。钙离子的协同结合 钙调素的两个钙结合结构域诱导构象 允许钙调蛋白激活特定靶标酶的变化。 钙调蛋白与相应的多肽的结合 兔平滑肌肌球蛋白轻链的钙调蛋白结合部位 用等温滴定的方法研究了肌动蛋白(SmMLCKp) 微量热法。束缚能量学依赖于 温度、pH、Ca~(2+)浓度和NaC l浓度 下定决心。研究发现，钙调素与SMMLCKp的结合 在热焓(H)、热容(Cp)、 和室温附近的熵(S)，表明它是一种 由热能驱动的过程，这在熵上是不利的。从… 这些结果表明，疏水效应--An 有利于非极性蛋白质基团去除的熵效应 来自水-不是钙调蛋白的主要驱动力-smMLCKp 承认。虽然大量的非极性侧链是 埋藏在结合上的这些主要通过形成稳定的络合物 密密麻麻的范德华相互作用。装订 在酸性pH下进行了研究，以评估其贡献 静电相互作用对结合的影响。研究发现，搬到 酸性pH导致吉布斯自由能大幅度下降。 但结合热没有变化，表明静电 相互作用对束缚能只起到了熵作用。 的可达表面积和原子堆积密度 钙调素-smMLCKp晶体 结构进行分析，并讨论与 实验数据。

Calmodulin is a small protein involved in the regulation of a wide variety of intracellular processes. The cooperative binding of Ca2+ to calmodulin's two Ca2+ binding domains induces conformational changes which allow calmodulin to activate specific target enzymes. The association of calmodulin with a peptide corresponding to the calmodulin binding site of rabbit smooth muscle myosin light chain kinase (smMLCKp) was studied using isothermal titration microcalorimetry. The dependence of the binding energetics on temperature, pH, Ca2+ concentration, and NaCl concentration were determined. It is found that the binding of calmodulin to smMLCKp proceeds with negative changes in enthalpy ( H), heat capacity ( Cp), and entropy ( S) near room temperature, indicating that it is an enthalpically driven process that is entropically unfavorable. From these results it is concluded that the hydrophobic effect - an entropic effect which favors the removal of nonpolar protein groups from water - is not a major driving force in calmodulin-smMLCKp recognition. Although a large number of nonpolar side chains are buried upon binding these stabilize the complex primarily by forming tightly packed van der Waals interactions with one another. Binding at acidic pH was studied in order to assess the contribution of electrostatic interactions to binding. It is found that moving to acidic pH results in a large decrease in the Gibbs free energy of binding but no change in the enthalpy, indicating that electrostatic interactions contribute only entropically to the binding energetics. The accessible surface area and atomic packing density of the calmodulin-smMLCKp crystal structure are analyzed, and the results discussed in relation to the experimental data.