Glycoside Hydrolase Family 75

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• Author:
• Responsible Curator: ^^^Ryszard Brzezinski^^^

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Glycoside Hydrolase Family GH75
Clan	Not assigned
Mechanism	Inverting
Active site residues	Inferred
CAZy DB link
https://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 primarily of 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.