Conformations and molecular interactions of poly-γ-glutamic acid as a soluble microbial product in aqueous solutions.
Conformations and molecular interactions of poly-γ-glutamic acid as a soluble microbial product in aqueous solutions.
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水溶液中可溶性微生物产物聚-γ-谷氨酸的构象和分子相互作用
DOI：
10.1038/s41598-017-13152-2
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发表时间：
2017-10-06
影响因子：
4.6
通讯作者：
Shi QS
中科院分区：
文献类型：
--
作者：
Wang LL;Chen JT;Wang LF;Wu S;Zhang GZ;Yu HQ;Ye XD;Shi QS
溶解性微生物产物（SMPs）在自然环境和工程系统中备受关注。在这项工作中，主要由芽孢杆菌属产生的聚 -γ - 谷氨酸（γ - PGA）在水溶液中的pH诱导构象变化和分子相互作用方面进行了研究；相应地，其沉降系数分布和黏度也得到了阐明。实验结果表明，pH对γ - PGA的结构和分子相互作用有显著影响。γ - PGA酸形式（γ - PGA - H）的构象为棒状，而γ - PGA钠盐形式（γ - PGA - Na）的构象为球状。γ - PGA二级结构中从α - 螺旋到无规卷曲的转变是这种形状变化的主要原因。随着pH升高，γ - PGA - H结构中的分子内氢键减少，分子内静电斥力增加；然而，γ - PGA的沉降系数分布取决于分子间相互作用而非分子内相互作用。在较高pH值下，浓度对分子间静电斥力和链缠结有更显著的影响。因此，在pH为8.9时，γ - PGA的沉降系数分布在0.1到1.0 g/L之间有显著变化，并且当pH从2.3升高到6.0时，γ - PGA（5% w/v）的黏度显著增加。
Soluble microbial products (SMPs) are of significant concern in the natural environment and in engineered systems. In this work, poly-γ-glutamic acid (γ-PGA), which is predominantly produced by Bacillus sp., was investigated in terms of pH-induced conformational changes and molecular interactions in aqueous solutions; accordingly, its sedimentation coefficient distribution and viscosity were also elucidated. Experimental results indicate that pH has a significant impact on the structure and molecular interactions of γ-PGA. The conformation of the γ-PGA acid form (γ-PGA-H) is rod-like while that of the γ-PGA sodium form (γ-PGA-Na) is sphere-like. The transformation from α-helix to random coil in the γ-PGA secondary structure is primarily responsible for this shape variation. The intramolecular hydrogen bonds in the γ-PGA-H structure decrease and intramolecular electrostatic repulsion increases as pH increases; however, the sedimentation coefficient distributions of γ-PGA are dependent on intermolecular interactions rather than intramolecular interactions. Concentration has a more substantial effect on intermolecular electrostatic repulsion and chain entanglement at higher pH values. Consequently, the sedimentation coefficient distributions of γ-PGA shift significantly at pH 8.9 from 0.1 to 1.0 g/L, and the viscosity of γ-PGA (5% w/v) significantly increases as pH increases from 2.3 to 6.0.
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