Glycoside Hydrolase Family 11

From CAZypedia

Author: Stephen Withers
Responsible Editor: Stephen Withers

Glycoside Hydrolase Family GH11
Clan	GH-C
Mechanism	retaining
Active site residues	known
CAZy DB link
http://www.cazy.org/fam/GH11.html

1 Substrate specificities
2 Kinetics and Mechanism
3 Catalytic Residues
4 Three-dimensional structures
5 Family Firsts
6 References

[edit] Substrate specificities

The enzymes in this family are endo-β-1,4-xylanases. No other activities have been observed.

[edit] Kinetics and Mechanism

Family GH11 xylanases are retaining enzymes, as first shown by NMR [1] and follow a classical Koshland double-displacement mechanism. No detailed analyses involving both steady state and pre-steady state kinetic studies have been reported. However, recent studies of the contributions of each substrate hydroxyl to transition state binding, thus to catalysis, have been reported [2].

xylanase reaction

[edit] Catalytic Residues

The catalytic nucleophile was first identified in the Bacillus circulans endo-xylanase as Glu78 in the sequence ITELD through trapping of the 2-deoxy-2-fluoroxylobiosyl-enzyme intermediate and subsequent peptide mapping via LC-MS/MS technologies [3]. The importance of the precise positioning of the nucleophile was probed by detailed kinetic analysis of mutants modified at that position [4]. The acid/base catalyst was first identified as Glu127 in this same enzyme through detailed mechanistic analysis of mutants at that position, which included azide rescue experiments [5]. Indeed detailed analyses of the role of the acid/base catalyst have been described. NMR based pKa measurements through the catalytic cycle reveal pKa cycling [6] while consequences of repositioning and removing the acid/base residue reveal its contributions [7].

[edit] Three-dimensional structures

Three-dimensional structures are available for a number of Family GH11 enzymes, the first solved being that of the Bacillus circulans xylanase [8]. As members of Clan GH-C they have a jellyroll fold. NMR assignment has allowed insights into both dynamics and electrostatics within the protein [8, 9, 10, 11].

[edit] Family Firsts

First sterochemistry determination: Bacillus circulans endo-xylanase Bcx by NMR [1]
First catalytic nucleophile identification: Bacillus circulans endo-xylanase Bcx by 2-fluoroglucose labeling [3]
First acid/base residue identification: Bacillus circulans endo-xylanase Bcx by rescue kinetics with mutants [5]
First 3-D structure: Bacillus circulans endo-xylanase Bcx [8]