Glycoside Hydrolase Family 15

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• Author: ^^^Pedro Coutinho^^^
• Responsible Curator: ^^^Pedro Coutinho^^^

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Glycoside Hydrolase Family GH15
Clan	GH-L
Mechanism	inverting
Active site residues	known
CAZy DB link
http://www.cazy.org/fam/GH15.html

Substrate specificities

Enzymes from this family hydrolyze the non-reducing end of a-glucosides by an inverting mechanism. At present, the most commonly characterized activity is glucoamylase (EC 3.2.1.3), also know as amyloglucosidase, but glucodextranase (EC 3.2.1.70) and α,α-trehalase (EC 3.2.1.28) activities have been described. It has been found that fungal glucoamylases present some substrate flexibility and are able to degrade not only α-1,4-glycosidic bonds but also α-1,6-, α-1,3- and α-1,2-bonds to a lower degree [1].

Kinetics and Mechanism

Family GH15 α-glycosidases are inverting enzymes, as first shown by Weil et al., 1954 [2] and follow a classical Koshland simple-displacement mechanism. Enzymes that have been well studied kinetically include Aspergillus and Rhizopus glucoamylases.

Catalytic Residues

The general acid was first identified in the Aspergillus awamori / Aspergillus niger glucoamylase as Glu179 following site-directed mutagenesis [3]. The general base was defined as Glu400 following the three-dimensional structure determination [4] and confirmed later on by site directed mutagenesis and kinetic studies [5]. Simultaneously the general base was identified in Clostridium sp. G0005 glucoamylase by chemical modification and mutagenesis [6].

Three-dimensional structures

Three-dimensional structures are available for a number of number of family GH15 enzymes, the first solved being that of Aspergillus awamori var. X100 glucoamylase [7]. All members of this family have (a/a)₆ barrel fold with the two key catalytic glutamic acid residues being approximately 200 residues apart in sequence and located at the loops following barrel α-helices 5 (general acid) and 11 (general base). Bacterial GH15 enzymes have in general an all β-strand super-β-sandwich preceding the catalytic (α/α)₆ barrel [8].

Family Firsts

First sterochemistry determination

Inverting mechanism in glucoamylase described by Weil et al., 1954 [2].

First general base identification

Aspergillus awamori var. X100 glucoamylase from crystal structure [4].

First general acid residue identification

Aspergillus niger glucoamylase from mutant kinetic analysis [3].

First 3-D structure

Aspergillus awamori var. X100 glucoamylase by X-ray cristallography [7].

References

1. Meagher MM and Reilly PJ. (1989). Kinetics of the hydrolysis of di- and trisaccharides with Aspergillus niger glucoamylases I and II. Biotechnol Bioeng. 1989;34(5):689-93. DOI:10.1002/bit.260340513 |

2. Weil CE, Burch RJ, Van Dyk JW. An α-amyloglucosidase that produces β-glucose, Cereal Chem 1954; 31 150–158.

3. Sierks MR, Ford C, Reilly PJ, and Svensson B. (1990). Catalytic mechanism of fungal glucoamylase as defined by mutagenesis of Asp176, Glu179 and Glu180 in the enzyme from Aspergillus awamori. Protein Eng. 1990;3(3):193-8. DOI:10.1093/protein/3.3.193 |
4. Harris EM, Aleshin AE, Firsov LM, and Honzatko RB. (1993). Refined structure for the complex of 1-deoxynojirimycin with glucoamylase from Aspergillus awamori var. X100 to 2.4-A resolution. Biochemistry. 1993;32(6):1618-26. DOI:10.1021/bi00057a028 |
5. Frandsen TP, Dupont C, Lehmbeck J, Stoffer B, Sierks MR, Honzatko RB, and Svensson B. (1994). Site-directed mutagenesis of the catalytic base glutamic acid 400 in glucoamylase from Aspergillus niger and of tyrosine 48 and glutamine 401, both hydrogen-bonded to the gamma-carboxylate group of glutamic acid 400. Biochemistry. 1994;33(46):13808-16. DOI:10.1021/bi00250a035 |
6. Ohnishi H, Matsumoto H, Sakai H, and Ohta T. (1994). Functional roles of Trp337 and Glu632 in Clostridium glucoamylase, as determined by chemical modification, mutagenesis, and the stopped-flow method. J Biol Chem. 1994;269(5):3503-10. | Google Books | Open Library
7. Aleshin A, Golubev A, Firsov LM, and Honzatko RB. (1992). Crystal structure of glucoamylase from Aspergillus awamori var. X100 to 2.2-A resolution. J Biol Chem. 1992;267(27):19291-8. DOI:10.2210/pdb1gly/pdb |

[[Category:Glycoside Hydrolase Families|GHnnn]]