Revisiting Cation Complexation and Hydrogen Bonding of Single-Chain Polyguluronate Alginate,Biomacromolecules

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Revisiting Cation Complexation and Hydrogen Bonding of Single-Chain Polyguluronate Alginate
Biomacromolecules ( IF 5.5 ) Pub Date : 2021-08-30 , DOI: 10.1021/acs.biomac.1c00840
Zezhong John Li _{1,

2} , Simcha Srebnik ₁ , Orlando J Rojas _{1,

3}

Affiliation

Modifying the properties of bio-based materials has garnered increasing interest in recent years. In related applications, the ability of alginates to complex with metal ions has been shown to be effective in liquid-to-gel transitions, useful in the development of foodstuff and pharma products as well as biomaterials, among others. However, despite its ubiquitous use, alginate behavior as far as interactions with cations is not fully understood. Hence, this study presents a detailed comparison of alginate’s complexation with Na⁺ and Ca²⁺ and the involved intramolecular hydrogen bonding and biomolecular chain geometry. Using all-atom molecular dynamics simulations, we find that in contrast to accepted models, calcium cations strongly bind to alginate chains by disruption of hydrogen bonds between neighboring residues, stabilizing a left-hand, 3-fold helical chain structure that enhances chain stiffness. Hence, while present, the traditionally accepted egg-box binding mode was a minor subset of possible conformations. For a single chain, most of the cation binding occurred as single-cation interaction with a carboxyl group, without the coordination of other alginate oxygens. The monovalent Na⁺ ions were found to be mostly nonlocalized around alginate and therefore do not compete with intramolecular hydrogen bonding. The different binding modes observed for Na⁺ and Ca²⁺ contribute toward explaining the different solubility of sodium and calcium alginate.

中文翻译：

重新审视单链聚古洛糖醛酸海藻酸盐的阳离子络合和氢键

近年来，改变生物基材料的特性引起了越来越多的兴趣。在相关应用中，海藻酸盐与金属离子络合的能力已被证明在液体到凝胶的转变中是有效的，可用于食品和医药产品以及生物材料等的开发。然而，尽管它无处不在，但尚未完全了解藻酸盐与阳离子相互作用的行为。因此，本研究详细比较了藻酸盐与 Na ⁺和 Ca ²⁺的络合以及涉及分子内氢键和生物分子链几何结构。使用全原子分子动力学模拟，我们发现与公认的模型相比，钙阳离子通过破坏相邻残基之间的氢键而与藻酸盐链强烈结合，稳定左手的 3 重螺旋链结构，从而增强链刚度。因此，虽然存在，但传统上接受的蛋盒结合模式是可能构象的一小部分。对于单链，大多数阳离子结合以与羧基的单阳离子相互作用发生，没有其他藻酸盐氧的配位。单价 Na ⁺发现大部分离子不在海藻酸盐周围，因此不与分子内氢键竞争。观察到的 Na ⁺和 Ca ²⁺的不同结合模式有助于解释海藻酸钠和海藻酸钙的不同溶解度。

更新日期：2021-09-13

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