Kazan Institute of Biochemistry and Biophysics, FRC Kazan Scientific Center of RAS, Lobachevsky Str., 2/31, 420111, Kazan, Russian Federation.
Carbohydr Polym. 2020 Jan 1;227:115342. doi: 10.1016/j.carbpol.2019.115342. Epub 2019 Sep 20.
It is widely accepted that cation binding specifically favors chain ordering and gelling of κ-carrageenan. However, current insights into the exact sequence of binding and conformational rearrangements as well as into the structure of binding sites are controversial. In the present work, the FTIR-spectroscopy combined with the computer modelling has been used to reveal the relation between cation binding and the secondary structure transition upon thermoreversible gelation of the κ-carrageenan. Three states of sulfate groups were defined spectroscopically: one cation-free and two specific cation-bound states. The DFT calculations reveal two energetically inequivalent spatial structures of cation binding unit, formed due to the local conformational adjustment in neocarrabiose moiety. Besides a charge screening effect, the cation-bound conformation of neocarrabiose also favors the helix formation.
人们普遍认为，阳离子的结合特异性地有利于 κ-卡拉胶的链有序化和胶凝。然而，目前对于结合的准确顺序和构象重排以及结合位点的结构的理解存在争议。在本工作中，傅里叶变换红外光谱学（FTIR-spectroscopy）结合计算机建模被用于揭示 κ-卡拉胶的热可逆凝胶化过程中阳离子结合与二级结构转变之间的关系。硫酸根基团的三种状态在光谱上被定义：一种无阳离子状态和两种特定的阳离子结合状态。DFT 计算揭示了由于新卡拉胶部分的局部构象调整而形成的阳离子结合单元的两个能量不等价的空间结构。除了电荷屏蔽效应外，新卡拉胶的阳离子结合构象也有利于形成螺旋结构。
