Parsons Drew F, Duignan Timothy T, Salis Andrea
School of Engineering and Information Technology, Murdoch University, 90 South Street, Murdoch, Western Australia 6150, Australia.
Physical Science Division, Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352, USA.
Interface Focus. 2017 Aug 6;7(4):20160137. doi: 10.1098/rsfs.2016.0137. Epub 2017 Jun 16.
A theoretical model of haemoglobin is presented to explain an anomalous cationic Hofmeister effect observed in protein aggregation. The model quantifies competing proposed mechanisms of non-electrostatic physisorption and chemisorption. Non-electrostatic physisorption is stronger for larger, more polarizable ions with a Hofmeister series Li< K< Cs. Chemisorption at carboxylate groups is stronger for smaller kosmotropic ions, with the reverse series Li > K > Cs. We assess aggregation using second virial coefficients calculated from theoretical protein-protein interaction energies. Taking Cs to not chemisorb, comparison with experiment yields mildly repulsive cation-carboxylate binding energies of 0.48 for Li and 3.0 for K. Aggregation behaviour is predominantly controlled by short-range protein interactions. Overall, adsorption of the K ion in the middle of the Hofmeister series is stronger than ions at either extreme since it includes contributions from both physisorption and chemisorption. This results in stronger attractive forces and greater aggregation with K, leading to the non-conventional Hofmeister series K > Cs ≈ Li.
提出了一种血红蛋白理论模型，以解释在蛋白质聚集过程中观察到的异常阳离子霍夫迈斯特效应。该模型对非静电物理吸附和化学吸附的竞争机制进行了量化。对于具有霍夫迈斯特序列Li < K < Cs的更大、更可极化的离子，非静电物理吸附更强。对于较小的促溶剂离子，在羧基上的化学吸附更强，序列相反，为Li > K > Cs。我们使用从理论蛋白质-蛋白质相互作用能计算得到的第二维里系数来评估聚集情况。假设Cs不发生化学吸附，与实验结果比较得出，Li的阳离子-羧基结合能为0.48，K的为3.0，呈轻微排斥作用。聚集行为主要由短程蛋白质相互作用控制。总体而言，霍夫迈斯特序列中间的K离子的吸附比两端的离子更强，因为它包含了物理吸附和化学吸附的贡献。这导致了更强的吸引力和与K更大的聚集，从而产生了非传统的霍夫迈斯特序列K > Cs ≈ Li。
