Hydration Layer Coupling and Cooperativity in Phase Behavior of Stimulus Responsive Peptide Polymers
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- 作者：Dennis Kurzbach ; Wafa Hassouneh ; Jonathan R. McDaniel ; Eva A. Jaumann ; Ashutosh Chilkoti ; Dariush Hinderberger
- 刊名：The Journal of the American Chemical Society
- 出版年：2013
- 出版时间：July 31, 2013
- 年：2013
- 卷：135
- 期：30
- 页码：11299-11308
- 全文大小：478K
- 年卷期：v.135,no.30(July 31, 2013)
- ISSN：1520-5126
文摘
It is shown that hydrophilic (backbone) and hydrophobic (side chain) hydration layers of elastin-like polypeptides (ELPs), a class of stimulus responsive peptide polymers that exhibit lower critical solution temperature (LCST) phase transition behavior, can exist in a coupled and decoupled state. The decoupled hydration state consists of hydrophobic and hydrophilic hydration layers that respond independently to temperature, while the coupled hydration state is characterized by a common, cooperative dehydration of both hydration layers. It is further shown that the primary sequence of an ELP can be tuned to exhibit either of the hydration layer coupling modes. Charged side chains lead to decoupling, while strongly hydrophobic side chains trigger stronger interaction between hydrophilic and hydrophobic hydration, leading to coupling of both layers. Further, for aprotic residues this coupling is fostered by decreasing bulkiness of hydrophobic side chains due to larger hydration numbers and water molecules mediating coupling between side chain and backbone hydration shells. For coupled hydration shells, the LCST phase transition characterized by spin probing continuous wave electron paramagnetic resonance spectroscopy is reminiscent of a first-order process even on nanoscopic length scales. In contrast, analogous synthetic polymers exhibit nanoscale phase transitions over a broad temperature range, indicating that their nanoscale phase behavior is not of first order. Hence, our results indicate that ELPs are the first identified class of polymers that exhibit a first-order inverse phase transition on nanoscopic length scales. These results may also provide insights into the role of hydration layers in governing the structure鈥揻unction relationship of intrinsically disordered proteins.