Thermostabilization of a thermophilic 1,4-a-glucan branching enzyme through C-terminal truncation

Authors: BAN, XIAOFENG - Jiangnan University; LIU, YITING - Jiangnan University; Zhang, Yuzhu; GU, ZHENGBIAO - Jiangnan University; LI, CAIMING - Jiangnan University; CHENG, LI - Jiangnan University; HONG, YAN - Jiangnan University; DHOBLE, ABHISHEK - University Of Illinois; LI, ZHAOFENG - Jiangnan University

Submitted to: International Journal of Biological Macromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2017
Publication Date: 10/10/2017
Citation: Ban, X., Liu, Y., Zhang, Y., Gu, Z., Li, C., Cheng, L., Hong, Y., Dhoble, A., Li, Z. 2017. Thermostabilization of a thermophilic 1,4-a-glucan branching enzyme through C-terminal truncation. International Journal of Biological Macromolecules. 107(Part B):1510-1518.

Interpretive Summary: Whether one wants to improve an enzyme’s suitability for industrial application at a desirable temperature or improve the marketability of food by reducing its allergenicity, the stability of proteins is an important factor that needs to be considered. However, the stability of proteins is poorly understood and, more often than not, changing the stability of an enzyme may result in a change in the flexibility and the activity of the protein, especially if the change is close to the active center. The N-terminus of a protein is often crucial for protein activation, recognition, and degradation and is considered a promising region for modification to manipulate protein stability. In contrast, researches to understand the functionality of the C-terminal region about the protein stability is lacking, though recent computational studies have suggested that there may be a correlation between terminal region motifs and the initial state of protein folding/native-state stability. This study investigated the effect of removing the last 26 residues of the 1,4-a-glucan branching enzyme from G. thermoglucosidans STB02. The C-terminal deletion increased the thermostability and the recovery ability of the enzyme without compromising enzymatic activity. Such information may be used in future studies on understanding the mechanisms of protein stability and on the developing the best strategies to stabilize/destabilize proteins that come from a variety of sources (such as psychrophilic and thermophilic sources) for agricultural and food industrial use.

Technical Abstract: Thermophilic proteins are useful for the detailed investigation of thermostability because they function efficiently at high temperatures. Comparison of the amino acid sequences and three-dimensional structures of mesophilic and thermophilic 1,4-a-glucan branching enzymes (GBEs) shows that the amino acid sequence of the last 26 residues at the C-terminal end of the GBE from Geobacillus thermoglucosidans STB02 (GBEGt, GenBank accession no. KJ660983) are not conserved, and that their 3-dimensionalstructure is flexible. These residues appear to be modified based upon a balance between flexibility and rigidity that is related to thermostability. In this study, a truncated mutant of GBEGt made by removing the last 26 residues from its C-terminal end was found to have increased thermostability and solubility, compared with the wild-type enzyme. Additionally, truncation of a portion of the C-terminus resulted in a decrease in aqueous stability. The circular dichroism spectra of GBEGt and GBEGt'C were also found to be different. These results suggest that deletion of flexible residues at the C-terminal end of GBEGt, which are located on the surface of the enzyme, enhances the thermostability of the enzyme without significantly compromising its enzymatic activity