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Glycoside Hydrolase Family 98
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| Glycoside Hydrolase Family GH98 | |
| Clan | Not assigned |
| Mechanism | Inverting |
| Active site residues | Known |
| CAZy DB link | |
| https://www.cazy.org/GH98.html | |
Substrate specificities
The glycoside hydrolases of this family are endo-β-galactosidases. No other activities have been reported. Family 98 glycoside hydrolases are unique in their specificity towards cleavage of the type II core [gal(β1-4)glcNAc] in the AB blood group antigens (EABase, Sp3GH98) and LewisY antigens (SpGH98) [1, 2, 3]. These enzymes are capable of processing these glycans when presented on cell surfaces thus destroying the antigens [1, 2].
Kinetics and Mechanism
Family GH98 galactosidases are inverting enzymes, as first shown by NMR monitoring of the Sp4GH98-catalyzed hydrolysis of the LewisY tetrasaccharide [2]. EABase was also shown to act through an inverting enzyme by NMR monitoring of the EABase catalysed hydrolysis of an artificial substrate, DNP-A-trisaccharide [3]. These results are contrary to the initial predictions made by Rigden [4]. EABase follows normal Michaelis-Menten kinetics [3].
Catalytic Residues
The general base, an aspartate and glutamate diad, and the general acid, glutamate, were identified through the crystal structures of Sp3GH98 and Sp4GH98 in complex with the A trisaccharide and H disaccharide, respectively, and confirmed by site-directed mutagenesis [2]. Similar results were obtained through kinetic studies of the corresponding acid and base mutants of EABase with the artificial substrate dinitrophenyl A-trisaccharide. Further biochemical evidence for the catalytic acid residue was obtained by comparison between the activity of the acid mutant and the pKa of the leaving group of the substrate [3].
Three-dimensional structures
The first crystal structures from family 98 were the Sp3GH98 and Sp4GH98 enzymes from S. pneumoniae in complex with the A trisaccharide and H disaccharide respectively [2]. Both structures feature a (α/β)8 barrel in the catalytic domain with an adjoining β-sandwich domain that contributes to the architecture of the active site and helps define the respective specificities of the enzymes [2]
Family Firsts
- First sterochemistry determination
- Streptococcus pneumoniae TIGR4 endo-beta-galactosidase Sp4GH98 by NMR [2].
- First general base identification
- Streptococcus pneumoniae SP3-BS71 endo-beta-galactosidase Sp3GH98 [2].
- Streptococcus pneumoniae TIGR4 endo-beta-galactosidase Sp4GH98 [2].
- First general acid identification
- Streptococcus pneumoniae SP3-BS71 endo-beta-galactosidase Sp3GH98 [2].
- Streptococcus pneumoniae TIGR4 endo-beta-galactosidase Sp4GH98 [2].
- First 3-D structures
- Streptococcus pneumoniae SP3-BS71 endo-beta-galactosidase Sp3GH98 [2].
- Streptococcus pneumoniae TIGR4 endo-beta-galactosidase Sp4GH98 [2].
References
- Anderson KM, Ashida H, Maskos K, Dell A, Li SC, and Li YT. (2005). A clostridial endo-beta-galactosidase that cleaves both blood group A and B glycotopes: the first member of a new glycoside hydrolase family, GH98. J Biol Chem. 2005;280(9):7720-8. DOI:10.1074/jbc.M414099200 |
- Higgins MA, Whitworth GE, El Warry N, Randriantsoa M, Samain E, Burke RD, Vocadlo DJ, and Boraston AB. (2009). Differential recognition and hydrolysis of host carbohydrate antigens by Streptococcus pneumoniae family 98 glycoside hydrolases. J Biol Chem. 2009;284(38):26161-73. DOI:10.1074/jbc.M109.024067 |
- Shaikh FA, Randriantsoa M, and Withers SG. (2009). Mechanistic analysis of the blood group antigen-cleaving endo-beta-galactosidase from Clostridium perfringens. Biochemistry. 2009;48(35):8396-404. DOI:10.1021/bi900991h |
- Rigden DJ (2005). Analysis of glycoside hydrolase family 98: catalytic machinery, mechanism and a novel putative carbohydrate binding module. FEBS Lett. 2005;579(25):5466-72. DOI:10.1016/j.febslet.2005.09.011 |