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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: Importance of c-terminal extension in thermophilic 1,4-a-glucan branching enzyme from geobacillus thermoglucosidans STB02

Author
item BAN, XIAOFENG - Jiangnan University
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: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2019
Publication Date: 10/25/2019
Citation: Ban, X., Li, C., Zhang, Y., Gu, Z., Cheng, L., Hong, Y., Li, Z. 2019. Importance of c-terminal extension in thermophilic 1,4-a-glucan branching enzyme from geobacillus thermoglucosidans STB02. Applied Biochemistry and Biotechnology. 190:1010–1022. https://doi.org/10.1007/s12010-019-03150-7.
DOI: https://doi.org/10.1007/s12010-019-03150-7

Interpretive Summary: The 1,4-a-glucan branching enzyme (GBE) catalyzes the formation of branch points in liner polysaccharide chains. Branching of the polysaccharide can improve the physical and chemical properties of carbohydrates, including their solubility and degradation. Therefore, GBEs desired for many purposes in agricultural and food industries. The branching enzyme from Geobacillus thermoglucosidans STB02 is a thermophilic GBE which can function at relatively high temperatures. However, knowledge of the function of the C-terminal region and its extension is limited. C-terminal deletion analyses in this study showed that while the last domain of this thermophilic GBE is important for the structural integrity of a functional enzyme, the removal of 26 amino acids of the C-terminal domain improved its stability and its tolerance to the presence of metal ions. The results of this work may be used to design better glucan branching enzymes for the production of foods with improved carbohydrates in the future.

Technical Abstract: The tertiary structure of 1,4-a-glucan branching enzyme from Geobacillus thermoglucosidans STB02 consists of an N-terminal carbohydrate-binding domain, a TIM-barrel catalytic domain, a C-terminal all-beta domain, and a highly charged 26-amino-acid C-terminal extension. Among these domains, the functional roles of the C-terminal extension are the least understood. In this study, the functional significance of C-terminal domain and its extension were assessed using a C-terminal deletion analysis. Mutants lacking of seven or more residues of the C-terminal all-beta domain could not be detected in lysates of their Escherichia coli expression strains, suggesting that an intact all-beta domain is required for structural stability. In contrast, deleting the C-terminal extension resulted in greater stability and solubility than the wild-type, as well as a lower sensitivity to the presence of added metal ions. Comparison of this mutant with the wild-type suggests that the interaction of metal ions with the C-terminal extension influences performance of this enzyme.