User:Jens Eklof

Glycoside Hydrolase Family 16
Clan	GH-B
Mechanism	retaining
Active site residues	known
CAZy DB link
http://www.cazy.org/fam/GH16.html

Substrate specificities

Family 16 enzymes cleave β-1,4 or β-1,3 glycosidic bonds in various glucans and galactans. Some members of this family have evolved to loose their hydrolytic activity and become strict transglycosylases.[1] The substrate specificities found in GH16 are: xyloglucan:xyloglucosyltransferases (EC 2.4.1.207), keratan-sulfate endo-1,4-β-galactosidases (EC 3.2.1.103), endo-1,3-β-glucanases (EC 3.2.1.39), endo-1,3(4)-β-glucanases (EC 3.2.1.6), lichenases (EC 3.2.1.73), β-agarases (EC 3.2.1.81), κ-carrageenases (EC 3.2.1.83) and xyloglucanases (EC 3.2.1.151).

Kinetics and Mechanism

Family 16 enzymes are retaining enzymes, as first shown by NMR [2] on an endo-1,3-1,4-β-D-glucan 4-glucanohydrolase from Bacillus licheniformis.

Catalytic Residues

The nucleophile was detected using an epoxyalkyl β-glycoside inhibitor and subsequent peptide identification by ESI-MS and Edman degradation on an endo-1,3-1,4-β-D-glucan 4-glucanohydrolase from Bacillus amyloliquefaciens.[3] The acid/base was found by mutation of all Asp and Glu into Asn and Gln respectively on an endo-1,3-1,4-β-D-glucan 4-glucanohydrolase from Bacillus licheniformis. [4]

Three-dimensional structures

Several family 16 three-dimensional structures have been solved of both archeal, bacterial and eukaryotic origin. The first solved 3-D structure was that of lichenase M from Paenibacillus macerans (PDB 1byh) in 1992. [5] The first eukaryotic 3-D structure was the xyloglucan endo-transglycosylase PttXET16-34 from Populus tremula×tremuloides (PDB 1umz).[1] The first archeal 3-D structure was a β-1,3-endoglucanase Lam16 from Pyrococcus furiosus (PDB 2vy0). [6]

Evolution of GH16

Family 16 is a member of clan GH-B together with family 7 with whom they share their β-jellyroll fold. The different specificities of family 16 has been proposed to have evoloved from a ancestral β-1,3-glucanase.[7]

Family firsts

First stereochemistry determination

Bacillus licheniformis 1,3-1,4-β-D-glucan 4-glucanohydrolase by NMR.[2]

First nucleophile identification

Bacillus amyloliquefaciens 1,3-1,4-β-D-glucan 4-glucanohydrolase.[3]

First general acid/base residue identification

Bacillus licheniformis 1,3-1,4-β-D-glucan 4-glucanohydrolase, first by sequence homology and mutational studies.[8] This was later verified by azide rescue of inactivated mutants.[4]

First 3-D structure

Paenibacillus macerans lichenase M by X-ray crystallography (PDB 1byh). [5]

Reference list

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