Crystal structure of BT1871 retaining glycosidase

Experimental Data Snapshot

  • Resolution: 2.30 Å
  • R-Value Free: 0.218 
  • R-Value Work: 0.186 
  • R-Value Observed: 0.186 

Starting Model: experimental
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Catalytic mechanism of retaining alpha-galactosidase belonging to glycoside hydrolase family 97.

Okuyama, M.Kitamura, M.Hondoh, H.Kang, M.S.Mori, H.Kimura, A.Tanaka, I.Yao, M.

(2009) J Mol Biol 392: 1232-1241

  • DOI: https://doi.org/10.1016/j.jmb.2009.07.068
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    Glycoside hydrolase family 97 (GH 97) is a unique glycoside family that contains inverting and retaining glycosidases. Of these, BtGH97a (SusB) and BtGH97b (UniProtKB/TrEMBL entry Q8A6L0), derived from Bacteroides thetaiotaomicron, have been characterized as an inverting alpha-glucoside hydrolase and a retaining alpha-galactosidase, respectively. Previous studies on the three-dimensional structures of BtGH97a and site-directed mutagenesis indicated that Glu532 acts as an acid catalyst and that Glu439 and Glu508 function as the catalytic base in the inverting mechanism. However, BtGH97b lacks base catalysts but possesses a putative catalytic nucleophilic residue, Asp415. Here, we report that Asp415 in BtGH97b is the nucleophilic catalyst based on the results of crystal structure analysis and site-directed mutagenesis study. Structural comparison between BtGH97b and BtGH97a indicated that OD1 of Asp415 in BtGH97b is located at a position spatially identical with the catalytic water molecule of BtGH97a, which attacks on the anomeric carbon from the beta-face (i.e., Asp415 is poised for nucleophilic attack on the anomeric carbon). Site-directed mutagenesis of Asp415 leads to inactivation of the enzyme, and the activity is rescued by an external nucleophilic azide ion. That is, Asp415 functions as a nucleophilic catalyst. The multiple amino acid sequence alignment of GH 97 members indicated that almost half of the GH 97 enzymes possess base catalyst residues at the end of beta-strands 3 and 5, while the other half of the family show a conserved nucleophilic residue at the end of beta-strand 4. The different positions of functional groups on the beta-face of the substrate, which seem to be due to "hopping of the functional group" during evolution, have led to divergence of catalytic mechanism within the same family.

  • Organizational Affiliation

    Research Faculty of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo 060-8589, Japan.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
641Bacteroides thetaiotaomicronMutation(s): 0 
Gene Names: BT_1871VPI-5482
Find proteins for Q8A6L0 (Bacteroides thetaiotaomicron (strain ATCC 29148 / DSM 2079 / JCM 5827 / CCUG 10774 / NCTC 10582 / VPI-5482 / E50))
Explore Q8A6L0 
Go to UniProtKB:  Q8A6L0
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ8A6L0
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.30 Å
  • R-Value Free: 0.218 
  • R-Value Work: 0.186 
  • R-Value Observed: 0.186 
  • Space Group: I 2 2 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 122.962α = 90
b = 167.1β = 90
c = 192.182γ = 90
Software Package:
Software NamePurpose
HKL-2000data collection
HKL-2000data reduction
SCALEPACKdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2009-10-06
    Type: Initial release
  • Version 1.1: 2011-07-13
    Changes: Version format compliance
  • Version 1.2: 2023-11-01
    Changes: Data collection, Database references, Derived calculations, Refinement description