Structural highlights
Publication Abstract from PubMedFructooligosaccharides and their anhydrides are widely used as health-promoting foods and prebiotics. Various enzymes acting on beta-D-fructofuranosyl linkages of natural fructan polymers have been used to produce functional compounds. However, enzymes that hydrolyze and form alpha-D-fructofuranosyl linkages have been less studied. Here, we identified the BBDE_2040 gene product from Bifidobacterium dentium (alpha-D-fructofuranosidase and difructose dianhydride I synthase/hydrolase from Bifidobacterium dentium [alphaFFase1]) as an enzyme with alpha-D-fructofuranosidase and alpha-D-arabinofuranosidase activities and an anomer-retaining manner. alphaFFase1 is not homologous with any known enzymes, suggesting that it is a member of a novel glycoside hydrolase family. When caramelized fructose sugar was incubated with alphaFFase1, conversions of beta-D-Frup-(2-->1)-alpha-D-Fruf to alpha-D-Fruf-1,2':2,1'-beta-D-Frup (diheterolevulosan II) and beta-D-Fruf-(2-->1)-alpha-D-Fruf (inulobiose) to alpha-D-Fruf-1,2':2,1'-beta-D-Fruf (difructose dianhydride I [DFA I]) were observed. The reaction equilibrium between inulobiose and DFA I was biased toward the latter (1:9) to promote the intramolecular dehydrating condensation reaction. Thus, we named this enzyme DFA I synthase/hydrolase. The crystal structures of alphaFFase1 in complex with beta-D-Fruf and beta-D-Araf were determined at the resolutions of up to 1.76 A. Modeling of a DFA I molecule in the active site and mutational analysis also identified critical residues for catalysis and substrate binding. The hexameric structure of alphaFFase1 revealed the connection of the catalytic pocket to a large internal cavity via a channel. Molecular dynamics analysis implied stable binding of DFA I and inulobiose to the active site with surrounding water molecules. Taken together, these results establish DFA I synthase/hydrolase as a member of a new glycoside hydrolase family (GH172). Identification of difructose dianhydride I synthase/hydrolase from an oral bacterium establishes a novel glycoside hydrolase family.,Kashima T, Okumura K, Ishiwata A, Kaieda M, Terada T, Arakawa T, Yamada C, Shimizu K, Tanaka K, Kitaoka M, Ito Y, Fujita K, Fushinobu S J Biol Chem. 2021 Nov;297(5):101324. doi: 10.1016/j.jbc.2021.101324. Epub 2021, Oct 22. PMID:34688653[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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