Structural basis for broad substrate specificity in higher plant beta-D-glucan glucohydrolases

Plant Cell. 2002 May;14(5):1033-52. doi: 10.1105/tpc.010442.

Abstract

Family 3 beta-D-glucan glucohydrolases are distributed widely in higher plants. The enzymes catalyze the hydrolytic removal of beta-D-glucosyl residues from nonreducing termini of a range of beta-D-glucans and beta-D-oligoglucosides. Their broad specificity can be explained by x-ray crystallographic data obtained from a barley beta-D-glucan glucohydrolase in complex with nonhydrolyzable S-glycoside substrate analogs and by molecular modeling of enzyme/substrate complexes. The glucosyl residue that occupies binding subsite -1 is locked tightly into a fixed position through extensive hydrogen bonding with six amino acid residues near the bottom of an active site pocket. In contrast, the glucosyl residue at subsite +1 is located between two Trp residues at the entrance of the pocket, where it is constrained less tightly. The relative flexibility of binding at subsite +1, coupled with the projection of the remainder of bound substrate away from the enzyme's surface, means that the overall active site can accommodate a range of substrates with variable spatial dispositions of adjacent beta-D-glucosyl residues. The broad specificity for glycosidic linkage type enables the enzyme to perform diverse functions during plant development.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Binding Sites
  • Carbohydrate Sequence
  • Catalysis
  • Cellobiose / chemistry
  • Cellobiose / metabolism
  • Disaccharides / chemistry
  • Disaccharides / metabolism
  • Glucan Endo-1,3-beta-D-Glucosidase / chemistry
  • Glucan Endo-1,3-beta-D-Glucosidase / genetics
  • Glucan Endo-1,3-beta-D-Glucosidase / metabolism
  • Glucans / chemistry
  • Glucans / metabolism
  • Glucosidases / chemistry
  • Glucosidases / genetics
  • Glucosidases / metabolism
  • Glycoside Hydrolases / chemistry
  • Glycoside Hydrolases / genetics
  • Glycoside Hydrolases / metabolism*
  • Kinetics
  • Models, Molecular
  • Molecular Sequence Data
  • Phylogeny
  • Plants / enzymology*
  • Plants / genetics
  • Protein Binding
  • Sequence Homology, Amino Acid
  • Structure-Activity Relationship
  • Substrate Specificity
  • Trisaccharides / chemistry
  • Trisaccharides / metabolism
  • beta-Glucosidase / chemistry
  • beta-Glucosidase / genetics
  • beta-Glucosidase / metabolism

Substances

  • 4-nitrophenyl S-glucopyranosyl-(1-3)-3-thioglucopyranosyl-1-3-glucopyranoside
  • Disaccharides
  • Glucans
  • Trisaccharides
  • laminaribiose
  • Cellobiose
  • Glucosidases
  • Glycoside Hydrolases
  • beta-D-glucan glucohydrolase
  • beta-Glucosidase
  • Glucan Endo-1,3-beta-D-Glucosidase
  • gentiobiose
  • sophorose

Associated data

  • GENBANK/AF102868
  • GENBANK/AW754572
  • PDB/1IEQ
  • PDB/1IEX
  • PDB/1J8V