Glycoside Hydrolase Family 49

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• Author: ^^^Takashi Tonozuka^^^
• Responsible Curator: ^^^Takashi Tonozuka^^^

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Glycoside Hydrolase Family GHnn
Clan	GH-N
Mechanism	inverting
Active site residues	known
CAZy DB link
http://www.cazy.org/fam/GHnn.html

Substrate specificities

Glycoside hydrolases of family 49 cleave α-1,6-linkages or α-1,4-linkages of polysaccharides containing α-1,6-linkages, dextran and pullulan. The major activities reported for this family of glycoside hydrolases are dextranase (EC 3.2.1.11). Dextran 1,6-α-isomaltotriosidase (EC 3.2.1.95) and isopullulanase (EC 3.2.1.57) activities have also been described.

Kinetics and Mechanism

Family GH49 α-glycosidases are inverting enzymes, as first shown by NMR on a dextranase Dex49A from Penicillium minioluteum.

Catalytic Residues

Three Asp residues (Asp376, Asp395, and Asp396 in Dex49A) are conserved in the catalytic centre of members of Clan GH-N, GH49 and GH28 enzymes, and all three of the Asp mutants of a GH49 enzyme, isopullulanase, lost their activities. The general acid was first identified in Dex49A from Penicillium minioluteum as Asp395 following the three-dimensional structure determination. To date, it is unclear whether either of the Asp residues (Asp376 and Asp396 in Dex49A) acts as a base in the reaction of both GH49 and GH28 enzymes.

Three-dimensional structures

GH49 enzymes display a two domain structure. The N-terminal domain is a β-sandwich and the C-terminal domain adopts a right-handed parallel β-helix.

Family Firsts

First stereochemistry determination

Cite some reference here, with a short (1-2 sentence) explanation [1].

First catalytic nucleophile identification

Cite some reference here, with a short (1-2 sentence) explanation [2].

First general acid/base residue identification

Cite some reference here, with a short (1-2 sentence) explanation [3].

First 3-D structure

Cite some reference here, with a short (1-2 sentence) explanation [4].

References

1. Comfort DA, Bobrov KS, Ivanen DR, Shabalin KA, Harris JM, Kulminskaya AA, Brumer H, and Kelly RM. (2007). Biochemical analysis of Thermotoga maritima GH36 alpha-galactosidase (TmGalA) confirms the mechanistic commonality of clan GH-D glycoside hydrolases. Biochemistry. 2007;46(11):3319-30. DOI:10.1021/bi061521n |

2. Sinnott, M.L. (1990) Catalytic mechanisms of enzymic glycosyl transfer. Chem. Rev. 90, 1171-1202. DOI: 10.1021/cr00105a006

3. He S and Withers SG. (1997). Assignment of sweet almond beta-glucosidase as a family 1 glycosidase and identification of its active site nucleophile. J Biol Chem. 1997;272(40):24864-7. DOI:10.1074/jbc.272.40.24864 |
4. Robert V. Stick and Spencer J. Williams. (2009) Carbohydrates. Elsevier Science.