Conformations and molecular interactions of poly-γ-glutamic acid as a soluble microbial product in aqueous solutions

• Published in: Scientific reports 2017-10, Vol.7 (1), p.12787-11, Article 12787
• Main Authors: Wang, Ling-Ling, Chen, Jian-Tao, Wang, Long-Fei, Wu, Sha, Zhang, Guang-zhao, Yu, Han-Qing, Ye, Xiao-dong, Shi, Qing-Shan
• Format: Article
• Language: English
• Subjects: 639/638/455/953; 639/638/455/958; Aqueous solutions; Conformation; Genetic transformation; Glutamic acid; Humanities and Social Sciences; Hydrogen bonding; multidisciplinary; Natural environment; pH effects; poly-γ-Glutamic acid; Protein structure; Random coil; Science; Science (multidisciplinary); Secondary structure; Sedimentation; Sedimentation & deposition; Sodium; Viscosity
• ISSN: 2045-2322; 2045-2322
• 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.