Glycoside Hydrolase Family 113

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• Author: ^^^Rohan Williams^^^ ^^^Spencer Williams^^^
• Responsible Curator: ^^^Spencer Williams^^^

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Glycoside Hydrolase Family GH113
Clan	GH-A
Mechanism	retaining
Active site residues	known
CAZy DB link
http://www.cazy.org/GH113.html

Substrate specificities

Only a single glycoside hydrolase of family GH113 has been characterized, intracellular AaManA from Alicyclobacillus acidocaldarius Tc-12-31 [1]. This thermoacidophilic organism was originally selected for its ability to hydrolyse konjac glucomannan [1]. The recombinantly-expressed enzyme possessed activity against polysaccharides containing β-1,4-mannosidic linkages, including significant activity against konjac glucomannan, and galactomannan from locust bean gum. Some activity was also observed against crystalline ivory nut mannan (an unsubstituted β-1,4-mannan) and guar gum (a more highly-substituted galactomannan) [1]. No activity was observed against the other polysaccharides and p-nitrophenyl glycosides tested, including p-nitrophenyl β- and α-mannosides.

Kinetics and Mechanism

Thin layer chromatographic analysis of the hydrolysis products of AaManA from A. acidocaldarius indicated ''endo''-type cleavage [1]. The products also displayed obvious signs of transglycosylation, and thus AaManA was assigned a retaining mechanism. The distance between the acid/base and nucleophile residues (assigned on the basis of structural comparison and mutagenesis, see below) is 4.75 Å [1]. Together, these data support a classical Koshland retaining mechanism. Kinetic analysis of mannooligosaccharides reveals a preference for pentamannosides and higher; a tetramannoside was hydrolysed with k_cat/K_M value approximately one quarter of that seen for the higher oligomers.

Catalytic Residues

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Three-dimensional structures

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Family Firsts

First stereochemistry determination

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First catalytic nucleophile identification

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First general acid/base residue identification

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First 3-D structure

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References

1. Zhang Y, Ju J, Peng H, Gao F, Zhou C, Zeng Y, Xue Y, Li Y, Henrissat B, Gao GF, and Ma Y. (2008). Biochemical and structural characterization of the intracellular mannanase AaManA of Alicyclobacillus acidocaldarius reveals a novel glycoside hydrolase family belonging to clan GH-A. J Biol Chem. 2008;283(46):31551-8. DOI:10.1074/jbc.M803409200 |

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