Glycoside Hydrolase Family 75

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• Author: Ryszard Brzezinski
• Responsible Curator: Ryszard Brzezinski

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Glycoside Hydrolase Family GH75
Clan	Not assigned
Mechanism	Inverting
Active site residues	Inferred
CAZy DB link
http://www.cazy.org/GH75.html

Substrate specificities

Glycoside hydrolases of family 75 include both eukaryotic (essentially fungal) and prokaryotic proteins. They have so far been characterized only from filamentous fungi. They are beta-1,4-chitosanases with endo-splitting activity [1, 2]. The analysis of the final product of hydrolysis of partially N-deacetylated chitosan by the GH75 chitosanase from Aspergillus fumigatus suggests that this enzyme cleaves preferentially GlcN-GlcN and GlcNAc-GlcN links in the polysaccharide chain [3].

Kinetics and Mechanism

Family GH46 enzymes are classified as inverting enzymes. This has been shown by ¹H NMR for the enzyme from Aspergillus fumigatus using chitosan as substrate [3].

Catalytic Residues

A site-directed mutagenesis study performed on the enzyme from Fusarium solani (expressed as a recombinant protein in Saccharomyces cerevisiae) showed that Asp175 and Glu188 are essential for catalysis [4]. This was confirmed by a study on the chitosanase from Aspergillus fumigatus (expressed as a recombinant protein in Escherichia coli) showing that the corresponding residues Asp160 and Glu169 are essential for catalysis [3]. Both residues are strictly conserved among eukaryotic and prokaryotic GH75 family members.

Three-dimensional structures

No three-dimensional structure has been solved for this family.

Family Firsts

First primary structure determination

Chitosanase from Fusarium solani f. sp. phaseoli [5].

First stereochemistry determination

Chitosanase from Aspergillus fumigatus [3].

First catalytic nucleophile identification

Not yet identified.

First general acid/base residue identification

Not yet identified.

First 3-D structure

Not yet determined.

References

1. Shimosaka M, Nogawa M, Ohno Y, and Okazaki M. Chitosanase from the pathogenic fungus, Fusarium solani f.sp. phaseoli - purification and some properties. Biosci. Biotech. Biochem. 1993 57, 231-235.

2. Cheng CY and Li YK. (2000). An Aspergillus chitosanase with potential for large-scale preparation of chitosan oligosaccharides. Biotechnol Appl Biochem. 2000;32(3):197-203. DOI:10.1042/ba20000063 |
3. Cheng CY, Chang CH, Wu YJ, and Li YK. (2006). Exploration of glycosyl hydrolase family 75, a chitosanase from Aspergillus fumigatus. J Biol Chem. 2006;281(6):3137-44. DOI:10.1074/jbc.M512506200 |
4. Shimosaka M, Sato K, Nishiwaki N, Miyazawa T, and Okazaki M. (2005). Analysis of essential carboxylic amino acid residues for catalytic activity of fungal chitosanases by site-directed mutagenesis. J Biosci Bioeng. 2005;100(5):545-50. DOI:10.1263/jbb.100.545 |

5. Shimosaka M, Kumehara M, Zhang X-Y, Nogawa M, and Okazaki M. Cloning and characterization of a chitosanase gene from the plant pathogenic fungus Fusarium solani. J. Ferment. Bioeng. 1996 82, 426-431.