Crystal Structure of the periplasmic alginate epimerase AlgG

Experimental Data Snapshot

  • Resolution: 2.10 Å
  • R-Value Free: 0.215 
  • R-Value Work: 0.188 
  • R-Value Observed: 0.189 

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This is version 1.2 of the entry. See complete history


Catalytic Mechanism and Mode of Action of the Periplasmic Alginate Epimerase AlgG.

Wolfram, F.Kitova, E.N.Robinson, H.Walvoort, M.T.Codee, J.D.Klassen, J.S.Howell, P.L.

(2014) J Biol Chem 289: 6006-6019

  • DOI: https://doi.org/10.1074/jbc.M113.533158
  • Primary Citation of Related Structures:  
    4NK6, 4NK8

  • PubMed Abstract: 

    Pseudomonas aeruginosa is an opportunistic pathogen that forms chronic biofilm infections in the lungs of cystic fibrosis patients. A major component of the biofilm during these infections is the exopolysaccharide alginate, which is synthesized at the inner membrane as a homopolymer of 1-4-linked β-D-mannuronate. As the polymer passages through the periplasm, 22-44% of the mannuronate residues are converted to α-L-guluronate by the C5-epimerase AlgG to produce a polymer of alternating β-D-mannuronate and α-L-guluronate blocks and stretches of polymannuronate. To understand the molecular basis of alginate epimerization, the structure of Pseudomonas syringae AlgG has been determined at 2.1-Å resolution, and the protein was functionally characterized. The structure reveals that AlgG is a long right-handed parallel β-helix with an elaborate lid structure. Functional analysis of AlgG mutants suggests that His(319) acts as the catalytic base and that Arg(345) neutralizes the acidic group during the epimerase reaction. Water is the likely catalytic acid. Electrostatic surface potential and residue conservation analyses in conjunction with activity and substrate docking studies suggest that a conserved electropositive groove facilitates polymannuronate binding and contains at least nine substrate binding subsites. These subsites likely align the polymer in the correct register for catalysis to occur. The presence of multiple subsites, the electropositive groove, and the non-random distribution of guluronate in the alginate polymer suggest that AlgG is a processive enzyme. Moreover, comparison of AlgG and the extracellular alginate epimerase AlgE4 of Azotobacter vinelandii provides a structural rationale for the differences in their Ca(2+) dependence.

  • Organizational Affiliation

    From the Program in Molecular Structure and Function, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Poly(beta-D-mannuronate) C5 epimerase491Pseudomonas syringae pv. tomato str. DC3000Mutation(s): 0 
Gene Names: algGPSPTO_1238
EC: 5.1.3
Find proteins for Q887Q3 (Pseudomonas syringae pv. tomato (strain ATCC BAA-871 / DC3000))
Explore Q887Q3 
Go to UniProtKB:  Q887Q3
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ887Q3
Sequence Annotations
  • Reference Sequence
Small Molecules
Modified Residues  1 Unique
IDChains TypeFormula2D DiagramParent
Query on MLY
Experimental Data & Validation

Experimental Data

  • Resolution: 2.10 Å
  • R-Value Free: 0.215 
  • R-Value Work: 0.188 
  • R-Value Observed: 0.189 
  • Space Group: P 32 2 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 126.616α = 90
b = 126.616β = 90
c = 97.708γ = 120
Software Package:
Software NamePurpose
DENZOdata reduction
SCALEPACKdata scaling
PDB_EXTRACTdata extraction
HKL-2000data collection

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2014-01-15
    Type: Initial release
  • Version 1.1: 2014-02-05
    Changes: Database references
  • Version 1.2: 2014-03-19
    Changes: Database references