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  • Title: High-throughput assay of levansucrase variants in search of feasible catalysts for the synthesis of fructooligosaccharides and levan.
    Author: Mardo K, Visnapuu T, Gromkova M, Aasamets A, Viigand K, Vija H, Alamäe T.
    Journal: Molecules; 2014 Jun 20; 19(6):8434-55. PubMed ID: 24955639.
    Abstract:
    Bacterial levansucrases polymerize fructose residues of sucrose to β-2,6 linked fructans-fructooligosaccharides (FOS) and levan. While β-2,1-linked FOS are widely recognized as prebiotics, the health-related effects of β-2,6 linked FOS are scarcely studied as they are not commercially available. Levansucrase Lsc3 (Lsc-3) of Pseudomonas syringae pv. tomato has very high catalytic activity and stability making it a promising biotechnological catalyst for FOS and levan synthesis. In this study we evaluate feasibility of several high-throughput methods for screening and preliminary characterization of levansucrases using 36 Lsc3 mutants as a test panel. Heterologously expressed and purified His-tagged levansucrase variants were studied for: (1) sucrose-splitting activity; (2) FOS production; (3) ability and kinetics of levan synthesis; (4) thermostability in a Thermofluor assay. Importantly, we show that sucrose-splitting activity as well as the ability to produce FOS can both be evaluated using permeabilized levansucrase-expressing E. coli transformants as catalysts. For the first time we demonstrate the key importance of Trp109, His113, Glu146 and Glu236 for the catalysis of Lsc3. Cost-effective and high-throughput methods presented here are applicable not only in the levansucrase assay, but have a potential to be adapted for high-throughput (automated) study of other enzymes.
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