Kubiak-Ossowska Karina, Cwieka Monika, Kaczynska Agnieszka, Jachimska Barbara, Mulheran Paul A
Department of Chemical and Process Engineering, University of Strathclyde, James Weir Building, 75 Montrose Street, Glasgow G1 1XJ, UK.
Phys Chem Chem Phys. 2015 Oct 7;17(37):24070-7. doi: 10.1039/c5cp03910j. Epub 2015 Aug 28.
Hen Egg White Lysozyme (HEWL) is a widely used exemplar to study protein adsorption on surfaces and interfaces. Here we use fully atomistic Molecular Dynamics (MD) simulations, Multi-Parametric Surface Plasmon Resonance (MP-SPR), contact angle and zeta potential measurements to study HEWL adsorption at a silica surface. The simulations provide a detailed description of the adsorption mechanism and indicate that at pH7 the main adsorption driving force is electrostatics, supplemented by weaker hydrophobic forces. Moreover, they reveal the preferred orientation of the adsorbed protein and show that its structure is only slightly altered at the interface with the surface. This provides the basis for interpreting the experimental results, which indicate the surface adsorbs a close-packed monolayer at about pH10 where the surface has a large negative zeta potential and the HEWL is positively charged. At higher pH, the adsorption amount of the protein layer is greatly reduced due to the loss of charge on the protein. At lower pH, the smaller zeta potential of the surface leads to lower HEWL adsorption. These interpretations are complemented by the contact angle measurements that show how the hydrophobicity of the surface is greatest when the surface coverage is highest. The simulations provide details of the hydrophobic residues exposed to solution by the adsorbed HEWL, completing the picture of the protein layer structure.
鸡蛋清溶菌酶（HEWL）是研究蛋白质在表面和界面上吸附的一种广泛使用的范例。在此，我们使用全原子分子动力学（MD）模拟、多参数表面等离子体共振（MP-SPR）、接触角和zeta电位测量来研究HEWL在二氧化硅表面的吸附。模拟提供了吸附机制的详细描述，并表明在pH7时，主要吸附驱动力是静电作用，较弱的疏水力起辅助作用。此外，模拟揭示了吸附蛋白质的优先取向，并表明其结构在与表面的界面处仅略有改变。这为解释实验结果提供了基础，实验结果表明在约pH10时表面吸附了紧密堆积的单分子层，此时表面具有较大的负zeta电位且HEWL带正电荷。在较高pH下，由于蛋白质上电荷的丧失，蛋白质层的吸附量大大降低。在较低pH下，表面较小的zeta电位导致HEWL吸附降低。接触角测量补充了这些解释，其显示当表面覆盖率最高时表面的疏水性最大。模拟提供了被吸附的HEWL暴露于溶液中的疏水残基的细节，完善了蛋白质层结构的全貌。
