Glycoside Hydrolase Family 62

This page has been approved by the Responsible Curator as essentially complete. CAZypedia is a living document, so further improvement of this page is still possible. If you would like to suggest an addition or correction, please contact the page's Responsible Curator directly by e-mail.

• Author: Harry Gilbert and ^^^Casper Wilken^^^
• Responsible Curator: Harry Gilbert

---

Glycoside Hydrolase Family GH62
Clan	GH-F
Mechanism	inverting
Active site residues	Known
CAZy DB link
https://www.cazy.org/GH62.html

Substrate specificities

This small family of glycoside hydrolases comprises both eukaryotic and prokaryotic enzymes. All the characterized enzymes in this family are arabinofuranosidases and the majority act on xylose moieties in xylan and arabinose moieties in arabinan that are single substituted with α-1,2 and α-1,3-L-arabinofuranose side chains [1]. However, a single GH62 enzyme from Pencillium oxalicum exclusively act on the α-1,3-L-arabinofuranose side chains [2]. The GH62 enzymes also display limited non-specific arabinofuranosidase activity; for example the arabinofuranosidases exhibit no [3] or very little [4, 5] activity against 4-nitrophenyl α-L-arabinofuranoside. Several of these enzymes contain carbohydrate binding modules that target cellulose- [3] or xylan- [6].

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. Prior to 3D structural data the catalytic residues were 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 [7] predicts that the catalytic general acid and general base will be a Glu and Asp, respectively, while a second Asp modulates the pKa of the general acid.

Catalytic Residues

Asp (general acid) and Glu (general base), as suggested by tertiary structures [4, 5, 8] and supported by site-directed mutagenesis and kinetic data [4, 5].

Three-dimensional structures

Based on its location in clan F, enzymes from family GH62s are predicted to display a 5-fold β-propeller fold. This hypothesis was confirmed by three papers published in 2014 [4, 5, 8]. The predicted catalytic general acid, catalytic general base and pKa modulator [7] were also confirmed by mutagenesis data [4, 5]. The active site arabinose-containing pocket opens up into a cleft or channel that binds the xylooligosaccharides and thus the xylan chain. The residues that interact with the polysaccharide backbone were identified [4]. In this respect a conserved tyrosine, present on a mobile loop, was shown to make an important contribution to substrate binding through hydrophobic interactions with the arabinose located in the active site [9].

Family Firsts

First sterochemistry determination

No direct experimental proof but 3D structural information point to an inverting mechanism [4, 5, 8].

First general acid residue identification

3D structural data [4, 5, 8] in concert with supporting mutagenesis data [4, 5].

First general base residue identification

3D structural data [4, 5, 8] in concert with supporting mutagenesis data [4, 5].

First 3-D structure

Several papers in 2014 reveal the 5-fold β-propeller fold [4, 5, 8].

References

Error fetching PMID 2125205:
Error fetching PMID 14747991:
Error fetching PMID 9461488:
Error fetching PMID 9148759:
Error fetching PMID 24482228:
Error fetching PMID 24394409:
Error fetching PMID 24951792:
Error fetching PMID 28890404:
Error fetching PMID 28669588:
Error fetching PMID 29611040: