BP0997, GH138 enzyme targeting pectin rhamnogalacturonan II

Experimental Data Snapshot

  • Resolution: 1.60 Å
  • R-Value Free: 0.205 
  • R-Value Work: 0.154 
  • R-Value Observed: 0.156 

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Structural and functional analyses of glycoside hydrolase 138 enzymes targeting chain A galacturonic acid in the complex pectin rhamnogalacturonan II.

Labourel, A.Basle, A.Munoz-Munoz, J.Ndeh, D.Booth, S.Nepogodiev, S.A.Field, R.A.Cartmell, A.

(2019) J Biol Chem 294: 7711-7721

  • DOI: https://doi.org/10.1074/jbc.RA118.006626
  • Primary Citation of Related Structures:  
    6HZE, 6HZF, 6HZG

  • PubMed Abstract: 

    The metabolism of carbohydrate polymers drives microbial diversity in the human gut microbiome. The selection pressures in this environment have spurred the evolution of a complex reservoir of microbial genes encoding carbohydrate-active enzymes (CAZymes). Previously, we have shown that the human gut bacterium Bacteroides thetaiotaomicron ( Bt ) can depolymerize the most structurally complex glycan, the plant pectin rhamnogalacturonan II (RGII), commonly found in the human diet. Previous investigation of the RGII-degrading apparatus in Bt identified BT0997 as a new CAZyme family, classified as glycoside hydrolase 138 (GH138). The mechanism of substrate recognition by GH138, however, remains unclear. Here, using synthetic substrates and biochemical assays, we show that BT0997 targets the d-galacturonic acid-α-1,2-l-rhamnose linkage in chain A of RGII and that it absolutely requires the presence of a second d-galacturonic acid side chain (linked β-1,3 to l-rhamnose) for activity. NMR analysis revealed that BT0997 operates through a double displacement retaining mechanism. We also report the crystal structure of a BT0997 homolog, BPA0997 from Bacteroides paurosaccharolyticus , in complex with ligands at 1.6 Å resolution. The structure disclosed that the enzyme comprises four domains, including a catalytic TIM (α/β) 8 barrel. Characterization of several BT0997 variants identified Glu-294 and Glu-361 as the catalytic acid/base and nucleophile, respectively, and we observed a chloride ion close to the active site. The three-dimensional structure and bioinformatic analysis revealed that two arginines, Arg-332 and Arg-521, are key specificity determinants of BT0997 in targeting d-galacturonic acid residues. In summary, our study reports the first structural and mechanistic analyses of GH138 enzymes.

  • Organizational Affiliation

    From the Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom and.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
BPa0997 N-ter E361S893Phocaeicola paurosaccharolyticusMutation(s): 0 
Find proteins for A0A4V8GZY5 (Phocaeicola paurosaccharolyticus)
Explore A0A4V8GZY5 
Go to UniProtKB:  A0A4V8GZY5
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupA0A4V8GZY5
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 1.60 Å
  • R-Value Free: 0.205 
  • R-Value Work: 0.154 
  • R-Value Observed: 0.156 
  • Space Group: P 2 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 55.298α = 90
b = 68.379β = 90
c = 220.158γ = 90
Software Package:
Software NamePurpose
xia2data reduction
Aimlessdata scaling
pointlessdata scaling
Cootmodel building
MolProbitymodel building

Structure Validation

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Ligand Structure Quality Assessment 

Entry History & Funding Information

Deposition Data

Funding OrganizationLocationGrant Number
European Research CouncilUnited Kingdom322820

Revision History  (Full details and data files)

  • Version 1.0: 2019-03-20
    Type: Initial release
  • Version 1.1: 2019-03-27
    Changes: Data collection, Database references
  • Version 1.2: 2019-05-22
    Changes: Data collection, Database references
  • Version 2.0: 2020-07-29
    Type: Remediation
    Reason: Carbohydrate remediation
    Changes: Atomic model, Data collection, Derived calculations, Structure summary
  • Version 2.1: 2024-05-15
    Changes: Data collection, Database references, Structure summary