5FA0: The structure of the beta-3-deoxy-D-manno-oct-2-ulosonic acid transferase domain from WbbB

Kdo (3-deoxy-d-manno-oct-2-ulosonic acid) is an eight-carbon sugar mostly confined to Gram-negative bacteria. It is often involved in attaching surface polysaccharides to their lipid anchors. alpha-Kdo provides a bridge between lipid A and the core oligosaccharide in all bacterial LPSs, whereas an oligosaccharide of beta-Kdo residues links "group 2" capsular polysaccharides to (lyso)phosphatidylglycerol. beta-Kdo is also found in a small number of other bacterial polysaccharides. The structure and function of the prototypical cytidine monophosphate-Kdo-dependent alpha-Kdo glycosyltransferase from LPS assembly is well characterized. In contrast, the beta-Kdo counterparts were not identified as glycosyltransferase enzymes by bioinformatics tools and were not represented among the 98 currently recognized glycosyltransferase families in the Carbohydrate-Active Enzymes database. We report the crystallographic structure and function of a prototype beta-Kdo GT from WbbB, a modular protein participating in LPS O-antigen synthesis in Raoultella terrigena The beta-Kdo GT has dual Rossmann-fold motifs typical of GT-B enzymes, but extensive deletions, insertions, and rearrangements result in a unique architecture that makes it a prototype for a new GT family (GT99). The cytidine monophosphate-binding site in the C-terminal alpha/beta domain closely resembles the corresponding site in bacterial sialyltransferases, suggesting an evolutionary connection that is not immediately evident from the overall fold or sequence similarities.
PDB ID: 5FA0Download
MMDB ID: 139321
PDB Deposition Date: 2015/12/10
Updated in MMDB: 2016/05
Experimental Method:
x-ray diffraction
Resolution: 2.3  Å
Source Organism:
Similar Structures:
Biological Unit for 5FA0: dimeric; determined by author and by software (PISA)
Molecular Components in 5FA0
Label Count Molecule
Proteins (2 molecules)
Putative N-acetyl Glucosaminyl Transferase
Molecule annotation
Chemical (1 molecule)
* Click molecule labels to explore molecular sequence information.

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