Glycosidic bond specificity of glucansucrases: on the role of acceptor substrate binding residues

Abstract

Many lactic acid bacteria produce extracellular α-glucan polysaccharides using a glucansucrase and sucrose as glucose donor. The structure and the physicochemical properties of the α-glucans produced are determined by the nature of the glucansucrase. Typically, the α-glucans contain two types of α-glycosidic linkages, for example, (α1-2), (α1-3), (α1-4) or (α1-6), which may be randomly or regularly distributed. Usually, the α-glucan chains are also branched, which gives rise to an additional level of complexity. Even though the first crystal structure was reported in 2010, our current understanding of the structure–function relationships of glucansucrases is not advanced enough to predict the α-glucan specificity from the sequence alone. Nevertheless, based on sequence alignments and site-directed mutagenesis, a few amino acid residues have been identified as being important for the glycosidic bond specificity of glucansucrases. A new development in GH70 research was the identification of a cluster of α-glucan disproportionating enzymes. Here, we discuss the current insights into the structure–function relationships of GH70 enzymes in the light of the recently determined crystal structure of glucansucrases.

Keywords::

• alternansucrase
• dextransucrase
• glycoside hydrolase
• reuteransucrase
• lactic acid bacteria
• protein engineering

Declaration of interest: This project is jointly financed by the European Union, European Regional Development Fund and The Ministry of Economic Affairs, Agriculture and Innovation, Peaks in the Delta, the Municipality of Groningen, the Provinces of Groningen, Frysl n and Drenthe as well as the Dutch Carbohydrate Competence Center (CCC WP2c). The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.