摘要/Abstract
在不同酸度条件下（pH＝3.0，6.0，7.4，9.0）诱导人血清白蛋白（HSA）进行质子化或去质子化，以研究其与小分子2，2'，4，4'，5，6'-六溴联苯醚（BDE154）的结合情况.首先将HSA与BDE154进行半柔性对接，发现BDE154与HSA周围的残基，如：酪氨酸150、赖氨酸195、赖氨酸199等存在较强的疏水相互作用.然后通过分子动力学模拟技术研究HSA在不同质子化状态下的动力学行为和热力学性质，可知过多的正电荷使HSA或者HSA-BDE154的系统稳定性变差.最后对HSA-BDE154的结合自由能进行预测，并对分子动力学模拟结果进行二级结构分析，结果表明HSA-BDE154复合物体系中随着酸度的增大，配体的结合对HSA的去螺旋过程有促进的作用.
关键词: 质子化, 分子对接, 同步荧光, 动力学模拟
In this paper, human serum albumin (HSA) binding to small molecule 2,2',4,4',5,6'-hexabromodiphenyl ether (BDE154) is studied by means of inducing protonation or deprotonation at four different pH levels (pH=3.0, 6.0, 7.4, 9.0). Firstly, it has been indicated that the charge distribution on HSA is very uniform even after protonation of HSA at different pH levels. From this, it can be inferred that the uniform charge distribution makes the electrostatic forces between the amino acid residues of the ⅡA region of HSA aspartic acid (Asp),glutamate (Glu) and histidine (His) to gradually reach a relative equilibrium and thus stabilize the HSA conformation. The results from synchronous fluorescence spectroscopy show that BDE154 has been bind to the ⅡA region of HSA, and is more closely to tryptophan (Try), and that causes the fluorescence quenching of HSA. After that, the semi-flexible docking of HSA with BDE 154 reveals that BDE154 has a cationic-π-conjugated effect and strong hydrophobic interaction with the surrounding amino acids, such as tyrosine 150 (Tyr150), lysine 195 (Lys195), lysine 199 (Lys199), etc. Next, the dynamic and thermodynamic properties of HSA under different protonation conditions have been studied by using molecular dynamic simulation. The results of simulation also show that too much positive charge deteriorates the system stability of HSA or HSA-BDE154 complex. Then, the binding free energy of HSA-BDE154 complex under different protonation states has been predicted by MM-PBSA method, and the contribution of amino acid residues to free energy of binding has also been analyzed. In addition, lysine 199 (Lys199), leucine 238 (Leu238), arginine 257 (Arg257), alanine 261 (Ala261), and isoleucine 264 (Ile264) in the HSA, being located in the hydrophobic cavity in subdomain ⅡA, are the most important residues when binding with BDE154. Therefore, the hydrophobic interaction has been identified as the major driving force for the binding between HSA-BDE154 systems, which is consistent with the results of molecular docking and the analysis of binding free energy. Finally, the results of secondary structure analysis of molecular dynamics simulation show that the binding could promote the de-helix process of HSA by increasing the acidity in HSA-BDE154 complex system.
Key words: protonated, molecular docking, synchronous fluorescence, dynamic simulation
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