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Publication Abstract from PubMed

Fructans play important roles as reserve carbohydrates and stress protectants in plants, and additionally serve as prebiotics with emerging antioxidant properties. Different fructan types are synthesized by an array of different plant fructosyltransferases (FTs) belonging to family 32 of glycoside hydrolases (GH32), clustering together with GH68 in Clan-J. Here, the 3D structure of a plant FT from a native source, the Pachysandra terminalis 6-SST/6-SFT (Pt6-SST/6-SFT) is reported. Besides its 1-SST (1-kestose forming) and hydrolytic side activities, the enzyme uses sucrose to create graminan- and levan-type fructans, which are probably associated with cold tolerance in this species. Furthermore, a Pt6-SST/6-SFT complex with 6-kestose was generated, representing a genuine acceptor binding modus at the +1, +2 and +3 subsites in the active site. The enzyme shows a unique configuration in its active site vicinity, including a unique D/Q couple located at the +1 subsite playing a dual role in donor and acceptor substrate binding. Furthermore, it shows a unique orientation of some hydrophobic residues, probably contributing to its specific functionality. A model is presented showing the formation of a beta(2-6) fructosyl linkage on 6-kestose to create 6,6-nystose, a mechanism that differs from the creation of a beta(2-1) fructosyl linkage on sucrose to produce 1-kestose. The structures shed light on the evolution of plant FTs from their vacuolar invertase ancestors, and contribute to further understand the complex structure-function relationships within plant GH32 members. (c) 2011 The Authors. The Plant Journal(c) 2011 Blackwell Publishing Ltd.

Crystal structure of 6-SST/6-SFT from Pachysandra terminalis, a plant fructan biosynthesizing enzyme in complex with its acceptor substrate 6-kestose.,Lammens W, Le Roy K, Yuan S, Vergauwen R, Rabijns A, Van Laere A, Strelkov SV, Van den Ende W Plant J. 2011 Nov 18. doi: 10.1111/j.1365-313X.2011.04858.x. PMID:22098191^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.