Crystal structure of streptococcal beta-galactosidase

Experimental Data Snapshot

  • Resolution: 1.80 Å
  • R-Value Free: 0.210 
  • R-Value Work: 0.174 
  • R-Value Observed: 0.176 

Starting Model: experimental
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This is version 1.3 of the entry. See complete history


Structural insights into the substrate specificity of Streptococcus pneumoniae beta (1,3)-galactosidase BgaC

Cheng, W.Wang, L.Jiang, Y.L.Bai, X.H.Chu, J.Li, Q.Yu, G.Liang, Q.L.Zhou, C.Z.Chen, Y.X.

(2012) J Biol Chem 287: 22910-22918

  • DOI: https://doi.org/10.1074/jbc.M112.367128
  • Primary Citation of Related Structures:  
    4E8C, 4E8D

  • PubMed Abstract: 

    The surface-exposed β-galactosidase BgaC from Streptococcus pneumoniae was reported to be a virulence factor because of its specific hydrolysis activity toward the β(1,3)-linked galactose and N-acetylglucosamine (Galβ(1,3)NAG) moiety of oligosaccharides on the host molecules. Here we report the crystal structure of BgaC at 1.8 Å and its complex with galactose at 1.95 Å. At pH 5.5-8.0, BgaC exists as a stable homodimer, each subunit of which consists of three distinct domains: a catalytic domain of a classic (β/α)(8) TIM barrel, followed by two all-β domains (ABDs) of unknown function. The side walls of the TIM β-barrel and a loop extended from the first ABD constitute the active site. Superposition of the galactose-complexed structure to the apo-form revealed significant conformational changes of residues Trp-243 and Tyr-455. Simulation of a putative substrate entrance tunnel and modeling of a complex structure with Galβ(1,3)NAG enabled us to assign three key residues to the specific catalysis. Site-directed mutagenesis in combination with activity assays further proved that residues Trp-240 and Tyr-455 contribute to stabilizing the N-acetylglucosamine moiety, whereas Trp-243 is critical for fixing the galactose ring. Moreover, we propose that BgaC and other galactosidases in the GH-35 family share a common domain organization and a conserved substrate-determinant aromatic residue protruding from the second domain.

  • Organizational Affiliation

    Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Glycosyl hydrolase, family 35
A, B
595Streptococcus pneumoniae TIGR4Mutation(s): 0 
Gene Names: SP_0060
Find proteins for A0A0H2UN19 (Streptococcus pneumoniae serotype 4 (strain ATCC BAA-334 / TIGR4))
Explore A0A0H2UN19 
Go to UniProtKB:  A0A0H2UN19
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupA0A0H2UN19
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 1 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on GOL

Download Ideal Coordinates CCD File 
C [auth A]
D [auth A]
E [auth A]
F [auth A]
G [auth B]
C [auth A],
D [auth A],
E [auth A],
F [auth A],
G [auth B],
H [auth B],
I [auth B],
J [auth B],
K [auth B],
L [auth B],
M [auth B],
N [auth B],
O [auth B]
C3 H8 O3
Experimental Data & Validation

Experimental Data

  • Resolution: 1.80 Å
  • R-Value Free: 0.210 
  • R-Value Work: 0.174 
  • R-Value Observed: 0.176 
  • Space Group: P 1 21 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 79.971α = 90
b = 79.3β = 106.94
c = 99.387γ = 90
Software Package:
Software NamePurpose
ADSCdata collection
HKL-2000data reduction
SCALAdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2012-05-30
    Type: Initial release
  • Version 1.1: 2012-06-13
    Changes: Database references
  • Version 1.2: 2013-08-07
    Changes: Database references
  • Version 1.3: 2023-11-08
    Changes: Data collection, Database references, Derived calculations, Refinement description