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Research Project: Defining, Measuring, and Mitigating Attributes that Adversely Impact the Quality and Marketability of Foods

Location: Healthy Processed Foods Research

Title: Potassium and sodium ions enhance the activity and thermostability of 1,4-a-glucan branching enzyme from Geobacillus thermoglucosidasius in the presence of glycerol

item Ban, Xiaofeng - Jiangnan University
item Dhoble, Abhishek - University Of Illinois
item Li, Caiming - Jiangnan University
item Zhang, Yuzhu
item Gu, Zhengbiao - Jiangnan University
item Cheng, Li - Jiangnan University
item Hong, Yan - Jiangnan University
item Li, Zhaofeng - Jiangnan University

Submitted to: International Journal of Biological Macromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2017
Publication Date: 4/17/2017
Citation: Ban, X., Dhoble, A., Li, C., Zhang, Y., Gu, Z., Cheng, L., Hong, Y., Li, Z. 2017. Potassium and sodium ions enhance the activity and thermostability of 1,4-a-glucan branching enzyme from Geobacillus thermoglucosidasius in the presence of glycerol. International Journal of Biological Macromolecules. 102:712-717.

Interpretive Summary: Many proteins from thermophilic microbial organisms have the potential of widespread usages in research and industrial applications due to their stability, and there is a constant desire to improve the stability and functionality of proteins. However, the stability of proteins is poorly understood. One of the natural attributes that help to stabilize proteins is the formation of electrostatic contact, but the design of internal electrostatic contacts to enhance protein stability is challenging because of the lack of comprehensive understanding of protein sequence-structure relationship. On the other hand, it may be possible to adjust electrostatic interactions by changing the protein’s environment to enhance their stability. This is especially true for proteins associated with mental factors. In this study, we investigated the effects of electrostatic interactions between metal ions and the thermophilic 1,4-a-glucan branching enzyme from Geobacillus thermoglucosidasius STB02 (GBE). Previous studies showed that the half-life of GBE dramatically decreases at 60°C and 65°C. The present study showed that K+ or Na+ in the presence of glycerol prolonged the half-life of GBE, while adding polyethylene glycols (PEGs) containing the same number of hydroxyl groups of the added glycerol did not enhance protein thermostability, suggesting that the combination of metal ions with glycerol stabilized the protein. The data may suggest a possible strategy for manipulating the stability of proteins by altering their sensitivity to salt environments.

Technical Abstract: Metal ions are essential for the performance of metal-dependent proteins and are known to be important for thermophilic proteins containing a large number of charged residues. The performance of thermophilic proteins may be influenced by metal ions through electrostatic interactions between the metal ions and charged residues. In this study, we investigated the effects of metal ions and glycerol on the activity and stability of the thermophilic 1,4-a-glucan branching enzyme (abbreviated GBE; EC from G. thermoglucosidasius STB02. The results indicated that K+ or Na+ enhance the performance of GBE, and that the addition of glycerol further increases the thermostability of GBE. The effects of K+ or Na+ with glycerol on the structure of GBE were further investigated using intrinsic fluorescence spectra and far-UV circular dichroism spectra. The results showed that more secondary structural elements are preserved by the addition of K+ or Na+ in the presence of glycerol. The improved maintenance of GBE structural elements after incubation may arise from electrostatic interactions introduced by the added salt, and glycerol provides a hydrophobic environment that strengthens these electrostatic contacts. This pr-vides a useful perspective for understanding the strategy of thermophilic adaptation used by proteins with plenty of charged residues.