Glycoside Hydrolase Family 43

• Author: Harry Gilbert
• Responsible Curator: Harry Gilbert

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Glycoside Hydrolase Family GH43
Clan	GH-F
Mechanism	inverting
Active site residues	not known
CAZy DB link
http://www.cazy.org/fam/GH43.html

Substrate specificities

The major activities reported for this family are alpha-L-arabinofuranosidases, endo-alpha-L-arabinanases (or endo-processive arabinanases) and beta-D-xylosidases. An enzyme with exo alpha1,3-galactanase has also been described. A significant number of enzymes in this family display both alpha-L-arabinofuranosidase and beta-D-xylosidase activity using aryl-glycosides as substrates. It is likely that the natural activity of these enzymes is conferred by the aglycone component of the substrate. Indeed, the arabionofuranosidase activities already reported target very different glycans. Thus, the Bacillus subtilis enzyme arabinoxylan alpha-L-arabinofuranohydrolase specifically removes arabinofuranose side chains that are linked either alpha1,2 or alpha1,3 to backbone xylose residues [1], while the arabinoxylan arabinofuranohydrolase-D3 (AXHd3) from Bifidobacterium adolescentis will remove an alpha1,3-linked arabinofuranose from xylans where the xylose residue is substituted at both alpha1,2 and alpha1,3 with arabinose. By contrast some arabinofuranosidases are exo-alpha-L-arabinanases display. It should be noted that in several plant cell wall degrading organisms there has been a dramtic expansion in GH43 family enzymes, which may reflect a more extensive range of specificities than described to date.

Kinetics and Mechanism

NMR, deploying arabinan as the substrate, showed that an endo-alpha1,5-arabinanase displays a single displacement or inverting mechanism [2]

Family Firsts

First sterochemistry determination

First catalytic nucleophile identification

First general acid/base residue identification

First 3-D structure

alpha-L-Arabinanase from Cellvibrio japonicus [1].

References

1. Nurizzo D, Turkenburg JP, Charnock SJ, Roberts SM, Dodson EJ, McKie VA, Taylor EJ, Gilbert HJ, and Davies GJ. (2002). Cellvibrio japonicus alpha-L-arabinanase 43A has a novel five-blade beta-propeller fold. Nat Struct Biol. 2002;9(9):665-8. DOI:10.1038/nsb835 |
2. Pitson SM, Voragen AG, and Beldman G. (1996). Stereochemical course of hydrolysis catalyzed by arabinofuranosyl hydrolases. FEBS Lett. 1996;398(1):7-11. DOI:10.1016/s0014-5793(96)01153-2 |