Farruggia B, García G, D'Angelo C, Picó G
Department of Physical Chemistry, Faculty of Biochemistry and Pharmaceutical Sciences, National University of Rosario, Argentina.
Int J Biol Macromol. 1997 Feb;20(1):43-51. doi: 10.1016/s0141-8130(96)01150-6.
Both polyethylene glycols (PEG) of MW 8,000 and that of 10000 stabilize the native compact state of human albumin showing negative preferential interaction with the protein. Interaction between these polymers and the protein is thermodynamically unfavorable, and becomes even more unfavorable for denatured protein whose surface areas are larger than those of native ones. PEG of low MW 1000 and 4000 did not show steric exclusion, interacting favorably with hydrophobic side chains made available when the protein was unfolded and leading to a stabilization of the unfolded state, which is manifested as a lowering of the thermal transition temperature. Perturbation of the absorption spectrum of albumin by PEGs confirms that at high temperature the polymers preferentially interact with the denatured state of albumin, but is excluded from the native state at low temperature. This observation is consistent with the fact that PEG is hydrophobic in nature and may interact favorably with the hydrophobic side chain exposed upon unfolding. The lower activation energy for thermal unfolding in the presence of PEG 1000 is in favour of preferential interaction of this polymer with human albumin. PEG of low MW favours the ionization of the tyrosine residues of albumin. It is apparent that pKa decreased with the increase in MW of synthetic polymer. Such variation might be a consequence of the change in dielectric constant at the domain of the protein by PEG binding.
分子量为8000和10000的聚乙二醇（PEG）均能稳定人血清白蛋白的天然紧密状态，且与该蛋白质呈现负优先相互作用。这些聚合物与蛋白质之间的相互作用在热力学上是不利的，对于表面积比天然蛋白质更大的变性蛋白质而言，这种不利性更为明显。低分子量的PEG（1000和4000）未表现出空间排斥作用，而是与蛋白质展开时暴露的疏水侧链发生有利相互作用，从而导致展开状态的稳定，这表现为热转变温度的降低。PEG对白蛋白吸收光谱的扰动证实，在高温下，聚合物优先与白蛋白的变性状态相互作用，但在低温下则被天然状态排斥。这一观察结果与PEG本质上具有疏水性且可能与展开时暴露的疏水侧链发生有利相互作用这一事实相符。在PEG 1000存在下，热展开的活化能较低，这有利于该聚合物与人血清白蛋白的优先相互作用。低分子量的PEG有利于白蛋白酪氨酸残基的电离。显然，随着合成聚合物分子量的增加，pKa降低。这种变化可能是PEG结合导致蛋白质结构域介电常数改变的结果。
