Department of Chemical and Process Engineering, University of Strathclyde, James Weir Building, 75 Montrose Street, Glasgow G1 1XJ, United Kingdom.
Langmuir. 2010 Oct 19;26(20):15954-65. doi: 10.1021/la102960m.
The mechanism of hen egg white lysozyme (HEWL) adsorption on a negatively charged, hydrophilic surface has been studied using atomistic molecular dynamics (MD) simulation. Sixteen 90 ns trajectories provide adequate data to allow a detailed description of the adsorption process to be formulated. Two distinct adsorption sites have been identified. The main one is located on the N,C-terminal protein face and comprises Arg128 (the crucial one), supplemented by Arg125, Arg5, and Lys1; the minor one is used accidentally and contains only Arg68. Adsorption of this protein is driven by electrostatics, where the orientation of the protein dipole moment defines the direction of protein movement. The diffusion range on the surface depends on protein side-chain penetration through the surface water layers. This is facilitated by the long-range electric field of the charged surface, which can align polar side chains to be perpendicular to the surface. A simulation of adsorption onto a neutral ionic surface shows no such surface water layer penetration. Therefore, protein flexibility is seen to be an important factor, and to adsorb the HEWL has to adjust its structure. Nevertheless, at a flat surface only a slight loss of α-helical content is required. The adsorbed HEWL molecule is oriented between side-on and end-on ways, where the angle between the protein long axis (which mostly approximates the dipole moment) and the surface varies between 45° and 90°. Simulations with targeted mutations confirm the picture that emerges from these studies. The active site is located on the opposite face to the main adsorption site; hence, the activity of the immobilized HEWL should not be affected by the surface interactions. Our results provide a detailed insight into the adsorption mechanism and protein mobility at the surface. This knowledge will aid the proper interpretation of experimental results and the design of new experiments and functional systems.
蛋清溶菌酶（HEWL）在带负电荷的亲水表面上的吸附机制已通过原子分子动力学（MD）模拟进行了研究。16 个 90ns 的轨迹提供了足够的数据，可以详细描述吸附过程。已经确定了两个不同的吸附位置。主要的吸附位置位于 N、C-末端蛋白质表面，包含 Arg128（关键的一个），辅以 Arg125、Arg5 和 Lys1；次要的吸附位置是偶然使用的，仅包含 Arg68。该蛋白质的吸附是由静电驱动的，其中蛋白质偶极矩的方向决定了蛋白质的运动方向。在表面上的扩散范围取决于蛋白质侧链穿透表面水层的程度。带电荷表面的长程电场有助于这种穿透，该电场可以使极性侧链与表面垂直排列。对吸附到中性离子表面的模拟表明不存在这种表面水层穿透。因此，蛋白质的灵活性被视为一个重要因素，而吸附 HEWL 必须调整其结构。然而，在平坦表面上只需要稍微损失α-螺旋含量。吸附的 HEWL 分子以侧挂和端挂方式取向，其中蛋白质长轴（主要近似于偶极矩）与表面之间的角度在 45°和 90°之间变化。针对突变体的模拟证实了这些研究得出的结论。活性位点位于与主要吸附位点相对的一侧；因此，固定化 HEWL 的活性不应受到表面相互作用的影响。我们的结果提供了对吸附机制和表面蛋白质迁移的详细了解。这些知识将有助于正确解释实验结果以及设计新的实验和功能系统。
