Difference between revisions of "Glycoside Hydrolase Family 62"

Revision as of 21:35, 31 August 2009

Glycoside Hydrolase Family GH62
Clan	GH-F
Mechanism	assumed to be inverting
Active site residues	inferred
CAZy DB link
http://www.cazy.org/fam/GH62.html

Substrate specificities

This small family of glycoside hydrolases comprises an equal number of eukaryotic and prokaryotic enzymes. All the characterized enzymes in this family are arabinofuranosidases that specifically cleave either alpha-1,2 or alpha-1,3-L-arabinofuranose side chains from xylans [1, 2]. The enzyme will not act on xylose moieties in xylan that are decorated at both O2 and O3 with an arabinose side chain. The enzyme also displays no non-specific arabinofuranosidase activity; for example it does not hydrolyse 4-nitrophenyl-alpha-L-arabinofuranose. Several of these enzymes contain cellulose [1] or xylan [3] binding CBMs.

Kinetics and Mechanism

While the catalytic mechanism of this family have not been formerly determined, likely reflecting the extremely quick rate of mutarotation displayed by arabinose, the enzyme is predicted to display a single displacement or inverting mechanism. This prediction is based on the location of GH62 in Clan F, the same clan occupied by GH43 (ClanF), which is an inverting family. Similarly, although the catalytic residues have not been determined using either biochemical or mutagenesis strategies, the identity of these residues is predicted from sequence homology with GH43 enzymes, given that both the catalytic mechanism and the catalytic apparatus are conserved in glycoside hydrolase families belonging to the same clan. Thus [4] predicts that the catalytic general acid and base will be a Glu and Asp, respectively, while a second Asp modulates the pKa of the general acid.

Catalytic Residues

Predicted to be an Asp (general acid) and Glu (general base)

Three-dimensional structures

Based on its location in Clan F, enzymes from family GH62s are predicted to display a 5-fold beta-propeller fold

Family Firsts

First sterochemistry determination: No experimental proof.
First general acid residue identification: No experimental proof.
First general base residue identification: No experimental proof.
First 3-D structure: No experimental proof.

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References

All Medline abstracts: PubMed

@@ Line 25: / Line 25: @@
 == Substrate specificities ==
-This small family comprises an equal number of eukaryotic and prokaryotic enzymes. All the characterized enzymes in this family are arabinofuranosidases that specifically cleave either alpha1,2 or alpha1,3 L-arabinofuranose side chains from xylans <cite>#1 #2</cite>. The enzyme will not act on xylose moieties in xylan that are decorated at both O2 and O3 with an arabinose side chain. The enzyme also displays no non-specific arabinofuranosidase activity; for example it does not hydrolyse 4-nitrophenyl-alpha-L-arabinofuranose. Several of these enzymes contain cellulose <cite>#1</cite> or xylan <cite>#3</cite> binding CBMs.
+This small family of [[glycoside hydrolases]] comprises an equal number of eukaryotic and prokaryotic enzymes. All the characterized enzymes in this family are arabinofuranosidases that specifically cleave either alpha-1,2 or alpha-1,3-L-arabinofuranose side chains from xylans <cite>#1 #2</cite>. The enzyme will not act on xylose moieties in xylan that are decorated at both O2 and O3 with an arabinose side chain. The enzyme also displays no non-specific arabinofuranosidase activity; for example it does not hydrolyse 4-nitrophenyl-alpha-L-arabinofuranose. Several of these enzymes contain cellulose <cite>#1</cite> or xylan <cite>#3</cite> binding CBMs.
 == Kinetics and Mechanism ==
-While the catalytic mechanism of this family have not been formerly determined, likely reflecting the extremely quick rate of mutarotation displayed by arabinose, the enzyme is predicted to display a single displacement or “inverting” mechanism. This prediction is based on the location of GH62 in Clan F, the same clan occupied by GH43 (ClanF), which is an inverting family. Similarly, although the catalytic residues have not been determined using either biochemical or mutagenesis strategies, the identity of these residues is predicted from sequence homology with GH43 enzymes, given that both the catalytic mechanism and the catalytic apparatus are conserved in glycoside hydrolase families belonging to the same clan. Thus <cite>#4</cite> predicts that the catalytic general acid and base will be a Glu and Asp, respectively, while a second Asp modulates the pKa of the general acid.
+While the catalytic mechanism of this family have not been formerly determined, likely reflecting the extremely quick rate of mutarotation displayed by arabinose, the enzyme is predicted to display a single displacement or [[inverting]] mechanism. This prediction is based on the location of GH62 in Clan F, the same clan occupied by GH43 (ClanF), which is an [[inverting]] family. Similarly, although the catalytic residues have not been determined using either biochemical or mutagenesis strategies, the identity of these residues is predicted from sequence homology with GH43 enzymes, given that both the catalytic mechanism and the catalytic apparatus are conserved in glycoside hydrolase families belonging to the same clan. Thus <cite>#4</cite> predicts that the catalytic general acid and base will be a Glu and Asp, respectively, while a second Asp modulates the pKa of the general acid.
 == Catalytic Residues ==
-Predicted to be an Asp (genral acid) and Glu (genral base)
+Predicted to be an Asp (general acid) and Glu (general base)
 == Three-dimensional structures ==
@@ Line 38: / Line 38: @@
 == Family Firsts ==
 ;First sterochemistry determination: No experimental proof.
-;First catalytic nucleophile identification: No experimental proof.
+;First general acid residue identification: No experimental proof.
-;First general acid/base residue identification: No experimental proof.
+;First general base residue identification: No experimental proof.
 ;First 3-D structure: No experimental proof.