Cao Yiping, Fang Yapeng, Nishinari Katsuyoshi, Phillips Glyn O
Glyn O. Phillips Hydrocolloid Research Centre, School of Food and Pharmaceutical Engineering, Faculty of Light Industry, Hubei University of Technology, Wuhan 430068, China.
Hubei Collaborative Innovation Centre for Industrial Fermentation, Hubei University of Technology, Wuhan 430068, China.
Sci Rep. 2016 Mar 31;6:23739. doi: 10.1038/srep23739.
Coupling of electrostatic complexation with conformational transition is rather general in protein/polyelectrolyte interaction and has important implications in many biological processes and practical applications. This work studied the electrostatic complexation between κ-carrageenan (κ-car) and type B gelatin, and analyzed the effects of the conformational ordering of κ-car induced upon cooling in the presence of potassium chloride (KCl) or tetramethylammonium iodide (Me4NI). Experimental results showed that the effects of conformational ordering on protein/polyelectrolyte electrostatic complexation can be decomposed into ionic binding and chain stiffening. At the initial stage of conformational ordering, electrostatic complexation can be either suppressed or enhanced due to the ionic bindings of K(+) and I(-) ions, which significantly alter the charge density of κ-car or occupy the binding sites of gelatin. Beyond a certain stage of conformational ordering, i.e., helix content θ > 0.30, the effect of chain stiffening, accompanied with a rapid increase in helix length ζ, becomes dominant and tends to dissociate the electrostatic complexation. The effect of chain stiffening can be theoretically interpreted in terms of double helix association.
在蛋白质/聚电解质相互作用中，静电络合与构象转变的耦合相当普遍，并且在许多生物过程和实际应用中具有重要意义。本工作研究了κ-卡拉胶（κ-car）与B型明胶之间的静电络合，并分析了在氯化钾（KCl）或四甲基碘化铵（Me4NI）存在下冷却时κ-car构象有序化的影响。实验结果表明，构象有序化对蛋白质/聚电解质静电络合的影响可分解为离子结合和链刚性增强。在构象有序化的初始阶段，由于K(+)和I(-)离子的离子结合，静电络合可能被抑制或增强，这显著改变了κ-car的电荷密度或占据了明胶的结合位点。在构象有序化的某个阶段之后，即螺旋含量θ > 0.30时，链刚性增强的影响，伴随着螺旋长度ζ的快速增加，变得占主导地位并倾向于使静电络合解离。链刚性增强的影响可以用双螺旋缔合理论来解释。
