State Key Laboratory of Applied Microbiology Southern China, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, Guangdong Open Laboratory of Applied Microbiology, Guangdong Institute of Microbiology, Guangzhou, 510070, China.
Faculty of Materials Science and Engineering, South China University of Technology, Guangzhou, 510640, China.
Sci Rep. 2017 Oct 6;7(1):12787. doi: 10.1038/s41598-017-13152-2.
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.
可溶微生物产物（SMPs）在自然环境和工程系统中受到广泛关注。在这项工作中，研究了主要由芽孢杆菌产生的聚-γ-谷氨酸（γ-PGA）在水溶液中 pH 诱导的构象变化和分子相互作用；相应地，还阐明了其沉降系数分布和粘度。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导致这种形状变化的主要原因。γ-PGA-H 结构中分子内氢键减少，分子内静电斥力增加，随着 pH 值的增加而增加；然而，γ-PGA 的沉降系数分布取决于分子间相互作用而不是分子内相互作用。在较高的 pH 值下，浓度对分子间静电斥力和链缠结的影响更大。因此，在 pH 8.9 时，γ-PGA 的沉降系数分布从 0.1 到 1.0 g/L 发生显著变化，并且随着 pH 值从 2.3 增加到 6.0，γ-PGA（5%w/v）的粘度显著增加。
