Interchain Overlap Affects Formation of Silk Fibroin Secondary Structures on Hydrophobic Polystyrene Surface Detected via Achiral/Chiral Sum Frequency Generation
作者：Xu Li, Guozhe Deng, Liang Ma, and Xiaolin Lu*
關鍵字：Protein secondary structures, achiral and chiral, interchain overlap
論文來源：期刊
具體來源：Langmuir 34, 32, 9453-9459
發表時間：2018年
我們發現，界面上蠶絲蛋白二級結構的形成與否與溶液的濃度直接關聯。我們借用了高分子臨界交疊濃度（C*）的概念。在C*以上，由于溶液中蛋白質分子鏈相互作用，在聚苯乙烯界面上形不成有序的二級結構，只有在外場（甲醇）的作用下才可以；在C*以下，由于溶液中蛋白質分子鏈處于無擾單鏈狀態，在聚苯乙烯界面上直接可形成有序的二級結構。這說明鏈鏈交疊或空間受限影響了蛋白質分子鏈折疊形成二級結構，在蛋白質的科學研究和工程化應用的過程中必須作為一個重要維度加以考慮。
Silk fibroin (SF) has been engineered in the biomedical applications on account of its structural robustness, biocompatibility and biodegradability. However, in situ study is still lacking with respect to the formation of SF secondary structures at the interface. In this paper, by using methanol as an inducing agent, the formation of SF secondary structures at the polystyrene (PS)/SF solution interfaces was detected with achiral and chiral sum frequency generation (SFG) vibrational spectroscopy. SF solutions with two concentrations above and below the critical overlapping concentration (C*) of SF (~1.8 mg/mL) were chosen, i.e. 90 mg/mL and 1 mg/mL. We found that above C*, before adding methanol to the protein solution, no ordered SF secondary structures could be detected at the PS/SF solution interface; oppositely, after adding methanol to the protein solution, ordered SF secondary structure, e.g. antiparallel b-sheet, could be formed at the PS/protein solution interface. Below C*, both before and after adding methanol to the SF solution, ordered SF secondary structure such as antiparallel b-sheet could be formed. Besides, the addition of methanol could induce the formation of an extended helical structure, verified by the achiral and chiral characteristic bands. Since C* represents a critical solution concentration above which the SF chains can interact with each other and below which the SF chains are isolated in the solution, this achiral/chiral SFG study emphasizes the importance of the chain-chain interaction or spatial confinement on the formation of the protein secondary structures, which providesan additional dimension for the future study of interfacial protein folding.
https://pubs.acs.org/articlesonrequest/AOR-eQNCt6AQUDIqbvYIEEFa