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A novel chicory fructanase can degrade common microbial fructan product profiles and displays positive cooperativity

Journal Contribution - Journal Article

Fructan metabolism in bacteria and plants relies on fructosyltransferases and fructanases. Plant fructanases only hydrolyse terminal Fru residues (fructan exohydrolase, FEH). Levan (β-2,6 linkages) is the most abundant fructan type in bacteria. Dicot fructan accumulators, such as chicory (Cichorium intybus), accumulate inulin (β-2,1 linkages), harbouring several 1-FEH isoforms for their degradation. Here, a novel chicory fructanase with high affinity for levan was characterized, providing evidence that such enzymes widely occur in higher plants. It is adapted to common microbial fructan profiles, but has low affinity towards chicory inulin, in line with a function in trimming of microbial fructans in the extracellular environment. Docking experiments indicate the importance of an N-glycosylation site close to the active site for substrate specificity. Optimal pH and temperature for levan hydrolysis are 5.0 and 43.7°C, respectively. Docking experiments suggested multiple substrate binding sites and levan-mediated enzyme dimerization, explaining the observed positive cooperativity (Hill kinetics). Alignments show a one amino acid shift in the position of a conserved DXX(R/K) couple, typical for sucrose binding in cell wall invertases. A possible involvement of plant fructanases in levan trimming is discussed, in line with the emerging “fructan detour” concepts, suggesting that levan oligosaccharides act as signalling entities during plant microbial interactions.
Journal: Journal of Experimental Botany
ISSN: 0022-0957
Issue: 5
Volume: 73
Pages: 1602 - 1622
Publication year:2022
Accessibility:Open