Glycoside Hydrolase Family 62

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• Author: Harry Gilbert
• Responsible Curator: Harry Gilbert

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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 α-1,2 or α-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 α-L-arabinofuranoside. 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, 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 β-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.

References

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1. Kellett LE, Poole DM, Ferreira LM, Durrant AJ, Hazlewood GP, and Gilbert HJ. (1990). Xylanase B and an arabinofuranosidase from Pseudomonas fluorescens subsp. cellulosa contain identical cellulose-binding domains and are encoded by adjacent genes. Biochem J. 1990;272(2):369-76. DOI:10.1042/bj2720369 |