Glycoside Hydrolase Family 84

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• Author: ^^^Ian Greig^^^
• Responsible Curator: ^^^David Vocadlo^^^

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Glycoside Hydrolase Family GH84
Clan	none
Mechanism	retaining
Active site residues	known
CAZy DB link
http://www.cazy.org/GH84.html

Substrate specificities

GH84 contains β-N-acetylglucosaminidases and β-N-acetylhyaluronidase activities. Human O-GlcNAcase is a cytosolic enzyme whose in vivo targets are glycoprotein serine and threonine residues modified by a single β-linked GlcNAc residue. In contrast to the β-hexosaminidases of GH20 a relaxed specificity for substitutions of the N-acyl group is observed with residues significantly more bulky than the N-acyl group being tolerated.[1]

Kinetics and Mechanism

Members of GH84 utilize a mechanism of neighbouring group participation, originally established through the use of free-energy relationships.[1] The most extensive kinetic studies have been carried out on human O-GlcNAcase. Substrate distortion.[2, 3] General acid catalysis operative for substrates possessing leaving groups with pKas greater than approximately XXX. For either O- or S-glycosides possessing leaving groups with pKas below XXX the leaving group will depart at the anion.[2, 4] Nuclear isoform (TRUNCATION) of Human O-GlcNAcase retains similar kinetic properties and inhibitory patterns as the cytosolic isoform consistent with hexosaminidase activity residing in the XXX domains.[5]

Catalytic Residues

Studies of two mutants of human O-GlcNAcase established that adjacent aspartate residues, Asp174 and Asp175, act as critical components of the catalytic machinery of this enzyme.[6]

The mutant Asp175Ala displayed marked reductions in activity (V and (V/K)) towards aryl N-acetylglucosaminides possessing poor leaving groups with smaller reductions being observed for both O-aryl and S-aryl N-acetylglucosaminides substrates possessing better leaving groups. Exogenous azide was found to partially rescue the activity of human O-GlcNAcase towards 3,4-dinitrophenylglucosaminide. These results identify Asp175 as the general acid catalyst.

The mutant Asp174Ala showed decreased activity towards O-aryl N-acetylglucosaminides possessing good leaving groups and it was argued that this is consistent with its role as a residue responsible for the orientation and polarization of the N-acyl nucleophile.

Three-dimensional structures

The reported crystallization of Clostridium perfringens NagJ[7] was followed by solved structures for that enzyme[8] and Bacteroides thetaiotaomicron b-hexosaminidase[8]. A series of crystallographic studies on Bacteroides thetaiotaomicron b-hexosaminidase using a variety of small molecules define the conformational itinerary for this family. Substrate distortion: WT + azepane [9], WT + difluoroacetyl [10], 4C1 intermediate: WT + thiazoline [1], general acid mutants Asp243Asn + 5-fluorooxazoline derived from b-1,5-difluoroglucosaminide,[10] Asp243Asn + oxazoline derived from 4-methylumbelliferyl b-glucosaminide,[10].

Family Firsts

First sterochemistry determination

¹H-NMR studies of human O-GlcNAcase established that the β-configured hemiacetal product is formed prior to anomerisation.[2].

First catalytic nucleophile identification

Cite some reference here, with a short (1-2 sentence) explanation [11].

First general acid/base residue identification

Studies of human O-GlcNAcase mutant Asp175Ala identify reactivity patterns (free energy relationships, pH-activity profiles) consistent with the action of Asp175 as the catalytic general acid/base.[6].

First 3-D structure

The structures of Bacteroides thetaiotaomicron O-GlcNAcase[12] and Clostridium perfringens NagJ[8].

References

1. Macauley MS, Whitworth GE, Debowski AW, Chin D, and Vocadlo DJ. (2005). O-GlcNAcase uses substrate-assisted catalysis: kinetic analysis and development of highly selective mechanism-inspired inhibitors. J Biol Chem. 2005;280(27):25313-22. DOI:10.1074/jbc.M413819200 |
2. Greig IR, Macauley MS, Williams IH, and Vocadlo DJ. (2009). Probing synergy between two catalytic strategies in the glycoside hydrolase O-GlcNAcase using multiple linear free energy relationships. J Am Chem Soc. 2009;131(37):13415-22. DOI:10.1021/ja904506u |
3. He Y, Macauley MS, Stubbs KA, Vocadlo DJ, and Davies GJ. (2010). Visualizing the reaction coordinate of an O-GlcNAc hydrolase. J Am Chem Soc. 2010;132(6):1807-9. DOI:10.1021/ja9086769 |
4. Macauley MS, Stubbs KA, and Vocadlo DJ. (2005). O-GlcNAcase catalyzes cleavage of thioglycosides without general acid catalysis. J Am Chem Soc. 2005;127(49):17202-3. DOI:10.1021/ja0567687 |
5. Macauley MS and Vocadlo DJ. (2009). Enzymatic characterization and inhibition of the nuclear variant of human O-GlcNAcase. Carbohydr Res. 2009;344(9):1079-84. DOI:10.1016/j.carres.2009.04.017 |

6. Cetinbaş N, Macauley MS, Stubbs KA, Drapala R, Vocadlo DJ. Identification of Asp174 and Asp175 as the key catalytic residues of human O-GlcNAcase by functional analysis of site-directed mutants. Biochemistry. 2006 Mar 21;45(11):3835-44.

   Note: Due to a problem with PubMed data, this reference is not automatically formatted. Please see these links out: DOI:10.1021/bi052370b PMID:16533067

7. Ficko-Blean E and Boraston AB. (2005). Cloning, recombinant production, crystallization and preliminary X-ray diffraction studies of a family 84 glycoside hydrolase from Clostridium perfringens. Acta Crystallogr Sect F Struct Biol Cryst Commun. 2005;61(Pt 9):834-6. DOI:10.1107/S1744309105024012 |
8. Rao FV, Dorfmueller HC, Villa F, Allwood M, Eggleston IM, and van Aalten DM. (2006). Structural insights into the mechanism and inhibition of eukaryotic O-GlcNAc hydrolysis. EMBO J. 2006;25(7):1569-78. DOI:10.1038/sj.emboj.7601026 |
9. Marcelo F, He Y, Yuzwa SA, Nieto L, Jiménez-Barbero J, Sollogoub M, Vocadlo DJ, Davies GD, and Blériot Y. (2009). Molecular basis for inhibition of GH84 glycoside hydrolases by substituted azepanes: conformational flexibility enables probing of substrate distortion. J Am Chem Soc. 2009;131(15):5390-2. DOI:10.1021/ja809776r |
10. He Y, Macauley MS, Stubbs KA, Vocadlo DJ, and Davies GJ. (2010). Visualizing the reaction coordinate of an O-GlcNAc hydrolase. J Am Chem Soc. 2010;132(6):1807-9. DOI:10.1021/ja9086769 |

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

12. Dennis RJ, Taylor EJ, Macauley MS, Stubbs KA, Turkenburg JP, Hart SJ, Black GN, Vocadlo DJ, and Davies GJ. (2006). Structure and mechanism of a bacterial beta-glucosaminidase having O-GlcNAcase activity. Nat Struct Mol Biol. 2006;13(4):365-71. DOI:10.1038/nsmb1079 |
13. 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 |
14. 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 |