On 17 October at 10:15 Karin Ernits will defend her doctoral thesis „Levansucrase Lsc3 and endo-levanase BT1760: characterization and application for the synthesis of novel prebiotics” .
TÜ MRI geneetika dotsent Tiina Alamäe
Professor Ebru Toksoy Öner, PhD, Department of Biotechnology, Faculty of Engineering, Marmara University, Istanbul, Turkey
Diet containing a sufficient amount of food fibre acts prebiotically – supports the growth of beneficial probiotic bacteria. Prebiotics are functional food ingredients, which pass the stomach unchanged and in the gut serve as energy and carbon source for probiotic bacteria such as bifidobacteria and lactobacilli. The most popular currently available prebiotics are inulin – a polymeric fructan extracted from chicory roots, and fructo-oligosaccharide (FOS) preparations produced from inulin by enzymatic hydrolysis. There is also another natural fructan – levan – which is synthesized mostly by bacteria. Levan and respective FOS have shown even higher prebiotic effect than those of inulin, but high production cost of these preparations hinders their study and utilization as a prebiotic supplement.
Our workgroup contributes extensively to synthesis and development of fructose-based novel prebiotics, focusing mainly on levan-type fructans. For that, we have been using two enzymatic approaches: i) synthesis of levan-type fructans using a levansucrase, and ii) hydrolysis of levan into FOS using an endo-levanase.
Levansucrase Lsc3 from a plant-associated bacterium Pseudomonas syringae pv. tomato was shown by us as a highly active and stable catalyst which makes it a perfect candidate for levan synthesis. Along with levan, levansucrase produces also FOS. Unfortunately, the mixture of FOS is full of glucose as an obligatory side-product of levansucrase reaction, and it contains both, inulin- and levan-type FOS. Isolation of levan-type FOS from this mixture is complicated.
We showed that a feasible way for levan-type FOS production is the hydrolysis of polymeric levan using the endo-levanase BT1760 from a human gut commensal Bacteroides thetaiotaomicron. The endo-levanase was able to hydrolyse every tested levan, preferring levan of plant origin. From the crystal structure analysis of BT1760, we concluded that levan chain should be bent into the substrate-binding pocket of the enzyme to enable the hydrolysis at the bottom of the cavity.