Crystal structure of the acid-base mutant (E477A) of the GH2 exo-beta-mannanase from Xanthomonas axonopodis pv. citri

Experimental Data Snapshot

  • Resolution: 2.20 Å
  • R-Value Free: 0.211 
  • R-Value Work: 0.169 
  • R-Value Observed: 0.171 

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Structural basis of exo-beta-mannanase activity in the GH2 family.

Domingues, M.N.Souza, F.H.M.Vieira, P.S.de Morais, M.A.B.Zanphorlin, L.M.Dos Santos, C.R.Pirolla, R.A.S.Honorato, R.V.de Oliveira, P.S.L.Gozzo, F.C.Murakami, M.T.

(2018) J Biol Chem 293: 13636-13649

  • DOI: https://doi.org/10.1074/jbc.RA118.002374
  • Primary Citation of Related Structures:  
    6BYC, 6BYE, 6BYG, 6BYI

  • PubMed Abstract: 

    The classical microbial strategy for depolymerization of β-mannan polysaccharides involves the synergistic action of at least two enzymes, endo-1,4-β-mannanases and β-mannosidases. In this work, we describe the first exo-β-mannanase from the GH2 family, isolated from Xanthomonas axonopodis pv. citri (XacMan2A), which can efficiently hydrolyze both manno-oligosaccharides and β-mannan into mannose. It represents a valuable process simplification in the microbial carbon uptake that could be of potential industrial interest. Biochemical assays revealed a progressive increase in the hydrolysis rates from mannobiose to mannohexaose, which distinguishes XacMan2A from the known GH2 β-mannosidases. Crystallographic analysis indicates that the active-site topology of XacMan2A underwent profound structural changes at the positive-subsite region, by the removal of the physical barrier canonically observed in GH2 β-mannosidases, generating a more open and accessible active site with additional productive positive subsites. Besides that, XacMan2A contains two residue substitutions in relation to typical GH2 β-mannosidases, Gly 439 and Gly 556 , which alter the active site volume and are essential to its mode of action. Interestingly, the only other mechanistically characterized mannose-releasing exo-β-mannanase so far is from the GH5 family, and its mode of action was attributed to the emergence of a blocking loop at the negative-subsite region of a cleft-like active site, whereas in XacMan2A, the same activity can be explained by the removal of steric barriers at the positive-subsite region in an originally pocket-like active site. Therefore, the GH2 exo-β-mannanase represents a distinct molecular route to this rare activity, expanding our knowledge about functional convergence mechanisms in carbohydrate-active enzymes.

  • Organizational Affiliation

    From the Brazilian Bioethanol Science and Technology Laboratory and.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
859Xanthomonas citri pv. citri str. 306Mutation(s): 1 
Gene Names: XAC3075
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.20 Å
  • R-Value Free: 0.211 
  • R-Value Work: 0.169 
  • R-Value Observed: 0.171 
  • Space Group: P 1 21 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 68.707α = 90
b = 202.127β = 110.3
c = 79.095γ = 90
Software Package:
Software NamePurpose
XDSdata reduction
XSCALEdata scaling
PDB_EXTRACTdata extraction

Structure Validation

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Ligand Structure Quality Assessment 

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2018-07-18
    Type: Initial release
  • Version 1.1: 2019-01-30
    Changes: Data collection, Database references
  • Version 1.2: 2020-07-29
    Type: Remediation
    Reason: Carbohydrate remediation
    Changes: Data collection, Derived calculations, Structure summary
  • Version 1.3: 2024-03-13
    Changes: Data collection, Database references, Structure summary