Glycoside Hydrolase Family 11

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

Substrate specificities

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

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].

Description

Catalytic Residues

The catalytic nucleophile was first identified in the Bacillus circulans endo-glycanase (Cex) 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].

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 GHC they have a jellyroll barrel fold. NMR assignment has allowed insights into both dynamics and electrostatics within the protein [8], [9], [10], [11]. .

PICTURES? OVERALL STRUCTURE; ACTIVE SITE; CARTOON OF ACTIVE SITE SHOWING INTERACTIONS?

For example:

• 3-D Structure of Bruce Stone:

• Link to a XET structure picture:
  • http://www.rcsb.org/pdb/explore/explore.do?structureId=1UMZ

Family Firsts

First sterochemistry determination

Bacillus circulans endo-xylanase Bcx by NMR (pmid=1618761)

First nuc. ID

Bacillus circulans endo-xylanase Bcx by 2-fluoroglucose labeling (pmid=1678739)

First A/B ID

Bacillus circulans fimi endo-xylanase Bcx by rescue kinetics with mutants (pmid=7910761)

First 3-D structures of a (major subfamily)

Bacillus circulans endo-xylanase Bcx (pmid=8019418)

References

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1. Gebler J, Gilkes NR, Claeyssens M, Wilson DB, Béguin P, Wakarchuk WW, Kilburn DG, Miller RC Jr, Warren RA, and Withers SG. (1992). Stereoselective hydrolysis catalyzed by related beta-1,4-glucanases and beta-1,4-xylanases. J Biol Chem. 1992;267(18):12559-61. | Google Books | Open Library

2. pmid=Wicki In Press

5. MacLeod AM, Lindhorst T, Withers SG, and Warren RA. (1994). The acid/base catalyst in the exoglucanase/xylanase from Cellulomonas fimi is glutamic acid 127: evidence from detailed kinetic studies of mutants. Biochemistry. 1994;33(20):6371-6. DOI:10.1021/bi00186a042 |