View source for Glycoside Hydrolase Family 11

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{| {{Prettytable}} 
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|{{Hl2}} colspan="2" align="center" |'''Glycoside Hydrolase Family GH11'''
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|'''Clan'''    
|GH-C
|-
|'''Mechanism'''
|retaining
|-
|'''Active site residues'''
|known
|-
|{{Hl2}} colspan="2" align="center" |'''CAZy DB link'''
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| colspan="2" |http://www.cazy.org/fam/GH11.html
|}
</div>

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

== Kinetics and Mechanism ==
Family GH11 xylanases are retaining enzymes, as first shown by NMR <cite>1</cite> 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 <cite>2</cite>. 

[[Image:XYLANASE REACTION.gif|thumb|Description]] 

== Catalytic Residues ==
The catalytic nucleophile was first identified in the ''Bacillus circulans'' endo-xylanase as Glu78 in the sequence IT'''<u>E</u>'''LD through trapping of the 2-deoxy-2-fluoroxylobiosyl-enzyme intermediate and subsequent peptide mapping via LC-MS/MS technologies <cite>3</cite>. The importance of the precise positioning of the nucleophile was probed by detailed kinetic analysis of mutants modified at that position <cite>4</cite>. 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 <cite>5</cite>. 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 <cite>6</cite> while consequences of repositioning and removing the acid/base residue reveal its contributions <cite>7Lawson</cite>.

== 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 <cite>8</cite>. As members of Clan GH-C they have a jellyroll fold. NMR assignment has allowed insights into both dynamics and electrostatics within the protein <cite>8</cite>, <cite>9</cite>, <cite>10</cite>, <cite>11</cite>. .

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


==== For example: ====
* 3-D Structure of Bruce Stone:
[[Image:Bruce_stone_150x180.jpg]]

* 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 <cite>1</cite>
;First nuc. ID: Bacillus circulans endo-xylanase Bcx by 2-fluoroglucose labeling <cite>3</cite>
;First A/B ID: Bacillus circulans fimi endo-xylanase Bcx by rescue kinetics with mutants <cite>5</cite>
;First 3-D structures of a (major subfamily): Bacillus circulans endo-xylanase Bcx <cite>8</cite> 
== References ==
<biblio>
#1 pmid=1618761
#2 pmid=Wicki In Press
#3 pmid=7911679
#4 pmid=8756474 NUC
#5 pmid=7910761 
#6 pmid=8756457 
#7 pmid=9047328
#8 pmid=8019418
#9 pmid=8762143   
#10 pmid=9416621    
#11 pmid=10752613   


</biblio>