β‐Glucosidase, β‐galactosidase, family A cellulases, family F xylanases and two barley glycanases form a superfamily of enzymes wit 8‐fold β/α architecture and with two conserved glutamates near the carboxy‐terminal ends of β‐strands four and seven

[摘要]

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

[学科分类] 生物化学/生物物理

[关键词] Superfamily;Glycosyl hydrolase;Family F xylanase;8-Fold β/α-barrel;β(1–3) and β(1–3;1–4) glucanase;PDB;Brookhaven Protein Databank;xylA;xylanase A;GHS;(1–3)-β-glucanase;GHR;(1–3;1–4)β-glucanase;pNPC;p-nitrophenyl cellobioside;β-gal;β-galactosidase;s.d.m.;site directed mutagenesis