PelX is a UDP- N-acetylglucosamine C4-epimerase involved in Pel polysaccharide-dependent biofilm formation

J Biol Chem. 2020 Aug 21;295(34):11949-11962. doi: 10.1074/jbc.RA120.014555. Epub 2020 Jun 29.


Pel is a GalNAc-rich bacterial polysaccharide that contributes to the structure and function of Pseudomonas aeruginosa biofilms. The pelABCDEFG operon is highly conserved among diverse bacterial species, and Pel may therefore be a widespread biofilm determinant. Previous annotation of pel gene clusters has helped us identify an additional gene, pelX, that is present adjacent to pelABCDEFG in >100 different bacterial species. The pelX gene is predicted to encode a member of the short-chain dehydrogenase/reductase (SDR) superfamily, but its potential role in Pel-dependent biofilm formation is unknown. Herein, we have used Pseudomonas protegens Pf-5 as a model to elucidate PelX function as Pseudomonas aeruginosa lacks a pelX homologue in its pel gene cluster. We found that P. protegens forms Pel-dependent biofilms; however, despite expression of pelX under these conditions, biofilm formation was unaffected in a ΔpelX strain. This observation led us to identify a pelX paralogue, PFL_5533, which we designate here PgnE, that appears to be functionally redundant to pelX In line with this, a ΔpelX ΔpgnE double mutant was substantially impaired in its ability to form Pel-dependent biofilms. To understand the molecular basis for this observation, we determined the structure of PelX to 2.1 Å resolution. The structure revealed that PelX resembles UDP-GlcNAc C4-epimerases. Using 1H NMR analysis, we show that PelX catalyzes the epimerization between UDP-GlcNAc and UDP-GalNAc. Our results indicate that Pel-dependent biofilm formation requires a UDP-GlcNAc C4-epimerase that generates the UDP-GalNAc precursors required by the Pel synthase machinery for polymer production.

Keywords: PelX; PgnE; Pseudomonas; Pseudomonas aeruginosa; Pseudomonas protegens; X-ray crystallography; bacterial adhesion; biofilm; enzyme; epimerase; microbiology; polysaccharide; short-chain dehydrogenase/reductase.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Biofilms*
  • Carbohydrate Epimerases / genetics
  • Carbohydrate Epimerases / metabolism*
  • Polysaccharides, Bacterial / genetics
  • Polysaccharides, Bacterial / metabolism*
  • Pseudomonas / physiology*
  • Pseudomonas aeruginosa / physiology*
  • Uridine Diphosphate N-Acetylglucosamine / genetics
  • Uridine Diphosphate N-Acetylglucosamine / metabolism


  • Bacterial Proteins
  • Polysaccharides, Bacterial
  • Uridine Diphosphate N-Acetylglucosamine
  • Carbohydrate Epimerases

Supplementary concepts

  • Pseudomonas protegens

Associated data

  • PDB/1SB8