Effect of a single point mutation on the interaction of glucans with a glucansucrase from Leuconostoc mesenteroides NRRL B-1118

Authors: Cote, Gregory; Skory, Christopher - Chris

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/21/2016
Publication Date: 7/21/2016
Citation: Cote, G.L., Skory, C.D. 2016. Effect of a single point mutation on the interaction of glucans with a glucansucrase from Leuconostoc mesenteroides NRRL B-1118 [abstract]. International Carbohydrate Symposium. p. 93.

Interpretive Summary:

Technical Abstract: The type strain of the lactic acid bacterium Leuconostoc mesenteroides produces a water-insoluble glucan from sucrose via an extracellular glucansucrase. Substitution of an amino acid that is coupled with the +2 subsite adjacent to the transition stabilizer of this glucansucrase, results in significant changes in the structures and yields of the water-insoluble glucans produced. We will describe how these changes affect the ability of the glucansucrase to bind to exogenous glucans, and how these glucans can influence the yield, product structures, and kinetics of the mutant glucansucrases. The activity of the wild-type enzyme, with threonine at position 654, is not significantly activated by added dextran, and the yield of water-insoluble glucan from sucrose is only slightly increased by dextran. Mutant T654Y is not affected at all by the addition of dextran. However, several mutants exhibit markedly lower yields of glucan relative to the wild type; these lower yields can be partially or completely overcome by the addition of water-soluble dextran. Although evidence indicates that the soluble dextran is incorporated into water-insoluble glucan, the increased yields cannot be accounted for solely by incorporation of the dextran into insoluble product. Furthermore, these mutants are significantly activated by exogenous glucans. The addition of dextran does not markedly change the KM for sucrose in the mutants, but does increase the Vmax of the reaction. These effects apparently depend on the presence of unbranched sequences of alpha1-6-linked D-glucose units in the glucan. Mutations at threonine-654 appear not to affect binding to dextran, but may influence the conformation of the enzyme.