4FFG: Crystal Structure Of Levan Fructotransferase From Arthrobacter Ureafaciens In Complex With Dfa-Iv

Levan is beta-2,6-linked polymeric fructose and serves as reserve carbohydrate in some plants and microorganisms. Mobilization of fructose is usually mediated by enzymes such as glycoside hydrolase (GH), typically releasing a monosaccharide as a product. The enzyme levan fructotransferase (LFTase) of the GH32 family catalyzes an intramolecular fructosyl transfer reaction and results in production of cyclic difructose dianhydride, thus exhibiting a novel substrate specificity. The mechanism by which LFTase carries out these functions via the structural fold conserved in the GH32 family is unknown. Here, we report the crystal structure of LFTase from Arthrobacter ureafaciens in apo form, as well as in complexes with sucrose and levanbiose, a difructosacchride with a beta-2,6-glycosidic linkage. Despite the similarity of its two-domain structure to members of the GH32 family, LFTase contains an active site that accommodates a difructosaccharide using the -1 and -2 subsites. This feature is unique among GH32 proteins and is facilitated by small side chain residues in the loop region of a catalytic beta-propeller N-domain, which is conserved in the LFTase family. An additional oligosaccharide-binding site was also characterized in the beta-sandwich C-domain, supporting its role in carbohydrate recognition. Together with functional analysis, our data provide a molecular basis for the catalytic mechanism of LFTase and suggest functional variations from other GH32 family proteins, notwithstanding the conserved structural elements.
PDB ID: 4FFGDownload
MMDB ID: 101371
PDB Deposition Date: 2012/6/1
Updated in MMDB: 2012/09
Experimental Method:
x-ray diffraction
Resolution: 2.3  Å
Source Organism:
Similar Structures:
Biological Unit for 4FFG: monomeric; determined by author and by software (PISA)
Molecular Components in 4FFG
Label Count Molecule
Protein (1 molecule)
Levan Fructotransferase
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

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