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*
关键字：Protein secondary structures, achiral and chiral, interchain overlap
论文来源：期刊
具体来源：Langmuir 34, 32, 9453-9459
发表时间：2018年
我们发现，界面上蚕丝蛋白二级结构的形成与否与溶液的浓度直接关联。我们借用了高分子临界交叠浓度（C*）的概念。在C*以上，由于溶液中蛋白质分子链相互作用，在聚苯乙烯界面上形不成有序的二级结构，只有在外场（甲醇）的作用下才可以；在C*以下，由于溶液中蛋白质分子链处于无扰单链状态，在聚苯乙烯界面上直接可形成有序的二级结构。这说明链链交叠或空间受限影响了蛋白质分子链折叠形成二级结构，在蛋白质的科学研究和工程化应用的过程中必须作为一个重要维度加以考虑。
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