Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, Aligarh 202002, India.
Department of Biochemistry, Faculty of Dentistry, Jamia Millia Islamia, New Delhi 110025, India.
Int J Biol Macromol. 2019 May 1;128:385-390. doi: 10.1016/j.ijbiomac.2019.01.136. Epub 2019 Jan 25.
Alpha-2-macroglobulin (αM) is large glycoprotein present in the body fluids of vertebrates. It is an antiproteinase that inhibits a broad spectrum of proteases without the direct blockage of the protease active site. Curcumin, a yellow spice commonly used in India and several Asian countries, is reported to have anti-tumor and anti-inflammatory effects because of its antioxidant properties. In the present study, we have explored the interaction of curcumin with αM using various technique such as antiproteinase activity assay, spectroscopy. Changes in the secondary structure of αM following interaction with curcumin was investigated by CD and FT-IR spectroscopy. Thermodynamics of curcumin-αM binding were also analyzed by isothermal titration calorimetry to identify the number of binding sites, changes in enthalpy, entropy and Gibbs free energy changes for this interaction. Thermodynamics parameters reveal that the binding is exothermic in nature. Our results suggest that the binding of curcumin with αM induces a conformational change in the native form of protein that compromises its anti-proteinase activity. This exothermic and spontaneous interaction leads to alteration in the β-sheet content of the protein leading to subtle changes in conformational status of the protein leading possibly to loss in the antiproteinase potential of the inhibitor.
α2-巨球蛋白（αM）是脊椎动物体液中存在的一种大型糖蛋白。它是一种抗蛋白酶，能够抑制广谱蛋白酶，而不会直接阻断蛋白酶的活性位点。姜黄素是一种在印度和几个亚洲国家常用的黄色香料，由于其抗氧化特性，被报道具有抗肿瘤和抗炎作用。在本研究中，我们使用各种技术，如抗蛋白酶活性测定、光谱法，探索了姜黄素与αM 的相互作用。通过 CD 和傅里叶变换红外光谱研究了姜黄素与αM 相互作用后αM 二级结构的变化。通过等温滴定量热法分析了姜黄素-αM 结合的热力学，以确定结合位点的数量、焓变、熵变和吉布斯自由能变化。热力学参数表明，结合是放热的。我们的结果表明，姜黄素与αM 的结合诱导蛋白质天然构象发生变化，从而降低其抗蛋白酶活性。这种放热和自发的相互作用导致蛋白质β-折叠含量的改变，从而导致蛋白质构象状态的细微变化，可能导致抑制剂的抗蛋白酶潜力丧失。
