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Catalytic Site Atlas

CSA LITERATURE entry for 1ghs

E.C. nameglucan endo-1,3-beta-D-glucosidase
SpeciesHordeum vulgare (Barley)
E.C. Number (IntEnz) 3.2.1.39
CSA Homologues of 1ghs1aq0,1ghr,2cyg,3em5,3f55,
CSA Entries With UniProtID P15737
CSA Entries With EC Number 3.2.1.39
PDBe Entry 1ghs
PDBSum Entry 1ghs
MACiE Entry 1ghs

Literature Report

IntroductionTwo plant beta-glucan endohydrolases with distinct substrate specificities, thought to have evolved from the same higher enzyme, which both hydrolyse 1,3-beta-D-glucosidic linkages in 1,3-beta-D-glucans. Chain A is the isoenzyme GII, (1->3)-beta-glucanase with E.C code 3.2.1.39 and chain B is the isoenzyme EII (1->3, 1->4)- beta glucanase with E.C code 3.2.1.73. Isoenzyme GII can hydrolyse beta-glucans of fungal cell walls and may therefore contribute to plant defence strategies, whereas isoenzyme GII function in plant cell wall hydrolysis during mobilisation of the endosperm or in germinating grain during the growth of vegetative tissue. Both glucanases have essentially identical alpha/beta barrel folds, with a recognisable cleft where the active site is located in the same position with identical catalytic residues, however beyond the conserved patch that surrounds the catalytic amino acid residues, there are different amino acid substitutions along the substrate-binding cleft leading to different substrate specificities.
MechansimHydrolysis of the glycosidic bond takes place via general acid catalysis leading to retention of configuration. The general acid protonated Glu288 protonates the glycosidic oxygen aided by Lys282 and Gly279, followed by nucleophilic attack by Glu231, formation of an oxy-carbonium ion intermediate. This is then broken down via deprotonation of a water by Glu288, a second nucleophilic attack of the deprotonated water molecule and regeneration of Glu231 results.
Reaction

Catalytic Sites for 1ghs

Literature References

Notes:
Varghese JN
Three-dimensional structures of two plant beta-glucan endohydrolases with distinct substrate specificities.
Proc Natl Acad Sci U S A 1994 91 2785-2789
PubMed: 8146192
Høj PB
Molecular evolution of plant beta-glucan endohydrolases.
Plant J 1995 7 367-379
PubMed: 7757111
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