Beta-glucosidase, beta-galactosidase, family A cellulases, family F xylanases and two barley glycanases form a superfamily of enzymes with 8-fold beta/alpha architecture and with two conserved glutamates near the carboxy-terminal ends of beta-strands four and seven

FEBS Lett. 1995 Apr 10;362(3):281-5. doi: 10.1016/0014-5793(95)00252-5.


Comparison of the recently determined crystal structures Pseudomonas fluorescens subsp. cellulosa family F xylanase, (1-3)-beta-glucanase and (1-3,1-4)-beta-glucanase and the catalytic domain of E. coli beta-galactosidase reveals that they belong to a superfamily of 8-fold beta/alpha-barrels with similar amino acid residues at their active sites. In the three families that these enzymes represent, the nucleophile is a glutamate, which is located close to the carboxy-terminus of beta-strand seven. In addition all three enzymes have the sequence asparagine-glutamate close to the carboxy-terminus of beta-strand four. This glutamate has been identified as the acid/base in the family F xylanases and is essential for catalysis in beta-galactosidase. We suggest that the equivalent residue in the barley glucanases is the acid/base. Analysis of the sequences of family 1 beta-glucosidases and family 5 cellulases shows that these enzymes also belong to this superfamily which we call the 4/7 superfamily.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Binding Sites
  • Cellulase / chemistry
  • Endo-1,4-beta Xylanases
  • Escherichia coli / enzymology
  • Glucan 1,3-beta-Glucosidase
  • Glutamates / chemistry*
  • Glycoside Hydrolases / chemistry*
  • Glycoside Hydrolases / genetics
  • Hordeum / enzymology
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Conformation*
  • Pseudomonas fluorescens / enzymology
  • Sequence Alignment
  • Xylosidases / chemistry*
  • Xylosidases / genetics
  • beta-Galactosidase / chemistry
  • beta-Glucosidase / chemistry


  • Glutamates
  • Glycoside Hydrolases
  • Xylosidases
  • glycanase
  • beta-Glucosidase
  • beta-Galactosidase
  • Cellulase
  • Glucan 1,3-beta-Glucosidase
  • licheninase
  • Endo-1,4-beta Xylanases