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.
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.
Jenkins
J
J
Department of Protein Engineering, Reading Laboratory, UK.
Lo Leggio
L
L
Harris
G
G
Pickersgill
R
R
D000595:Amino Acid Sequence; D001665:Binding Sites; D002480:Cellulase / Q000737:chemistry; D043364:Endo-1,4-beta Xylanases; D004926:Escherichia coli / Q000201:enzymology; D043326:Glucan 1,3-beta-Glucosidase; D005971:Glutamates / Q000737:chemistry*; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000235:genetics; D001467:Hordeum / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011551:Pseudomonas fluorescens / Q000201:enzymology; D016415:Sequence Alignment; D014995:Xylosidases / Q000737:chemistry* / Q000235:genetics; D001616:beta-Galactosidase / Q000737:chemistry; D001617:beta-Glucosidase / Q000737:chemistry
D005971:Glutamates; D006026:Glycoside Hydrolases; D014995:Xylosidases; C020668:glycanase; D001617:beta-Glucosidase; D001616:beta-Galactosidase; D002480:Cellulase; D043326:Glucan 1,3-beta-Glucosidase; C028020:licheninase; D043364:Endo-1,4-beta Xylanases