Molecular basis of Ca2+-induced gelation in alginates and pectins:: The egg-box model revisited
Molecular basis of Ca2+-induced gelation in alginates and pectins:: The egg-box model revisited
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DOI：
10.1021/bm010008g
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发表时间：
2001-12-01
影响因子：
6.2
通讯作者：
Pérez, S
中科院分区：
文献类型：
--
作者：
Braccini, I;Pérez, S
对于许多离子多糖来说，在二价阳离子（如钙）存在下形成凝胶的能力是其生物功能和技术应用的关键。海藻酸盐和果胶尤其如此，其中α - l -(1-4)-古醛酸酯残基和α - d -半乳糖酸酯残基的规律分别产生了物理凝胶中涉及的聚合物链关联的有序模板。之前的一篇论文（Braccini; et al.）研究了这两种多糖钙相互作用的强度和立体特异性的分子基础。Carbohydr。Res. 1999, 119)。在目前的工作中，开发了一种新的分子建模程序；它包括一个配对过程，评估有序聚脲酸盐链与钙离子形成二聚体的所有可能的结合。从聚半乳糖酸酯和聚谷醛酸酯的稳定有序形式出发，计算了形成Ca2+桥接二聚体的所有可能方式；同时考虑了链的平行和反平行排列。尽管聚脲酸酯和聚半乳糖酸酯链的结构相似，但在链-链结合水平上存在显著差异。流行的“鸡蛋盒模型”在聚谷氨酸盐的情况下仍然可以参考。然而，它不能被用来描述果胶结区作为每个重复两个连续螯合位点的独特特征，这为链间结合提供了有利的熵贡献，这一开创性模型无法再现。这些结果的主体证实了钙凝胶化机制中的两阶段过程，其中强连接二聚体缔合的形成之后主要是弱二聚体间缔合的形成。受静电相互作用支配。
For many ionic polysaccharides, the ability to form gels in the presence of divalent cations such as calcium is the key to biological functions and technological applications. This is particularly true for alginates and pectins, where the regular occurrence of respectively alpha-L-(1-4)-guluronate residues and alpha-D-galacturonate residues generates ordered templates for polymer chain associations that are involved in physical gels. The molecular basis responsible for the strength and the stereospecificity of calcium interactions for the two polysaccharides were investigated in a previous paper (Braccini; et al. Carbohydr. Res. 1999, 119). In the present work, a novel molecular modeling procedure has been developed; it involves a pairing procedure that evaluates all the possible associations of the ordered polyuronate chains with calcium ions to form dimers. Starting from the stable ordered forms of polygalacturonate and polyguluronate, all possible ways to form Ca2+-bridged dimers were computed; the parallel and antiparallel relative arrangements of the chains, were also considered. Despite the structural analogy between polyguluronate and polygalacturonate chains, significant differences at the level of chain-chain associations are found. The popular "egg box model" can still be referred to in the case of polyguluronate. However, it cannot be used to describe a pectate junction zone as the unique feature of two consecutive chelation site per repeat, that provides a favorable entropic contribution to the interchain association is not reproduced by this pioneering model. The body of these results corroborates the two-stage process in the mechanism of calcium gelation, where the formation of strongly linked dimer associations is followed by the formation of weak inter-dimer associations mainly.. governed by electrostatic interactions.