Effects of Hofmeister Anions on the Phase Transition Temperature of Elastin-like Polypeptides

详细信息    查看全文

• 作者：Younhee Cho ; Yanjie Zhang ; Trine Christensen ; Laura B. Sagle ; Ashutosh Chilkoti ; Paul S. Cremer
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：November 6, 2008
• 年：2008
• 卷：112
• 期：44
• 页码：13765-13771
• 全文大小：230K
• 年卷期：v.112,no.44(November 6, 2008)
• ISSN：1520-5207

文摘

The modulation of the lower critical solution temperature (LCST) of two elastin-like polypeptides (ELPs) was investigated in the presence of 11 sodium salts that span the Hofmeister series for anions. It was found that the hydrophobic collapse/aggregation of these ELPs generally followed the series. Specifically, kosmotropic anions decreased the LCST by polarizing interfacial water molecules involved in hydrating amide groups on the ELPs. On the other hand, chaotropic anions lowered the LCST through a surface tension effect. Additionally, chaotropic anions showed salting-in properties at low salt concentrations that were related to the saturation binding of anions with the biopolymers. These overall mechanistic effects were similar to those previously found for the hydrophobic collapse and aggregation of poly(N-isopropylacrylamide), PNIPAM. There is, however, a crucial difference between PNIPAM and ELPs. Namely, PNIPAM undergoes a two-step collapse process as a function of temperature in the presence of sufficient concentrations of kosmotropic salts. By contrast, ELPs undergo collapse in a single step in all cases studied herein. This suggests that the removal of water molecules from around the amide moieties triggers the removal of hydrophobic hydration waters in a highly coupled process. There are also some key differences between the LCST behavior of the two ELPs. Specifically, the more hydrophilic ELP V₅A₂G₃-120 construct displays collapse/aggregation behavior that is consistent with a higher concentration of anions partitioning to polymer/aqueous interface as compared to the more hydrophobic ELP V₅-120. It was also found that larger anions could bind with ELP V₅A₂G₃-120 more readily in comparison with ELP V₅-120. These latter results were interpreted in terms of relative binding site accessibility of the anion for the ELP.