3UGH: Crystal Structure Of A 6-Sst6-Sft From Pachysandra Terminalis In Complex With 6-Kestose

Fructans play important roles as reserve carbohydrates and stress protectants in plants, and additionally serve as prebiotics with emerging antioxidant properties. Various fructan types are synthesized by an array of plant fructosyltransferases belonging to family 32 of the glycoside hydrolases (GH32), clustering together with GH68 in Clan-J. Here, the 3D structure of a plant fructosyltransferase from a native source, the Pachysandra terminalis 6-SST/6-SFT (Pt6-SST/6-SFT), is reported. In addition to 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 the vicinity of its active site, including a unique D/Q couple located at the +1 subsite that plays 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 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 fructosyltransferases from their vacuolar invertase ancestors, and contribute to further understanding of the complex structure-function relationships within plant GH32 members.
PDB ID: 3UGHDownload
MMDB ID: 95412
PDB Deposition Date: 2011/11/2
Updated in MMDB: 2011/12
Experimental Method:
x-ray diffraction
Resolution: 2.9  Å
Source Organism:
Similar Structures:
Biological Unit for 3UGH: monomeric; determined by author and by software (PISA)
Molecular Components in 3UGH
Label Count Molecule
Protein (1 molecule)
Sucrose:(sucrose/fructan) 6-fructosyltransferase
Molecule annotation
Chemicals (10 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB