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
https://www.cazy.org/GH15.html

Substrate specificities

Glycoside hydrolases of this family are exo-acting enzymes that hydrolyze the non-reducing end residues of α-glucosides. 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 single-step displacement mechanism. Enzymes that have been well studied kinetically include the 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 several GH15 family enzymes, the first solved being that of Aspergillus awamori var. X100 glucoamylase [7]. All members of this family have (α/α)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 Aspergillus niger glucoamylase deduced by optical rotation described by Weil et al., 1954 [2].

First sequence identification

Aspergillus niger glucoamylase by peptide sequencing [9].

First general acid identification

Aspergillus awamori glucoamylase from mutant kinetic analysis [3].

First general base identification

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

First 3-D structure

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

References

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

9. Svensson S, Larsen K, Svendsen I, Boel E. The complete amino acid sequence of the glycoprotein, glucoamylase G1, from Aspergillus niger. Carlsberg Res Commun 1983; 48(6) 529-44 DOI: 10.1007/BF02907555