Glycoside Hydrolase Family 51

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• Author: ^^^Yuval Shoham^^^
• Responsible Curator: ^^^Yuval Shoham^^^

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Glycoside Hydrolase Family GH51
Clan	GH-A
Mechanism	retaining
Active site residues	known
CAZy DB link
http://www.cazy.org/fam/GH51.html

Substrate specificities

The majority of the enzymes from this family hydrolyze the glycosidic bond between L-arabinofuranosides side chains of hemicelluloses such as arabinoxylan, arabinogalactan, and L-arabinan. A few enzymes of the family exhibit beta 1-4 endoglucanase activity towards carboxy methyl cellulose and xylan [1].

This is an example of how to make references to a journal article [2]. (See the References section below). Multiple references can go in the same place like this [2, 3]. You can even cite books using just the ISBN [4]. References that are not in PubMed can be typed in by hand [5].

Kinetics and Mechanism

Family GH51 L-arabinfuranosidases are retaining enzymes and follow a classical Koshland double-displacement mechanism. Due to the fast mutarotation and tautomerization rates of arabinose, the stereochemical course of the reaction was determined in presence of methanol and followed by NMR spectroscopy [6, 7, 8]. Enzymes that have been well studied kinetically include the Geobacillus stearothermophilus T-6 and Thermobacillus xylanilyticus alpha L-arabinofuranosidases, for which a detailed kinetic study was performed including kinetics with aryl-α-L-arabinofuranosides bearing various leaving groups, Brønsted plots for the E175A acid-base catalytic residue and azide-rescue for the E294A nucleophilc mutant [7, 8, 9].

Catalytic Residues

The catalytic acid-base was first identified in Thermobacillus xylanilyticus (Glu176) [7] and in Geobacillus stearothermophilus T-6 (Glu175) alpha-arabinofuranosidases [8] using kinetic analysis, pH dependence profiles, and azide rescue of the catalytic mutant. The catalytic nucleophile was first identified in Geobacillus stearothermophilus alpha-arabinofuranosidase through detailed kinetic studies for the catalytic mutant including azide rescue.

Three-dimensional structures

Three-dimensional structures for GH51 arabinofuranosidases are available for G. stearothermophilus [10] C. thermocellum [11] and Thermobacillus xylanilyticus [12]. The enzyme in solution is a hexamer (can be described as a trimer of dimmers) and each monomer is organized into two domains: a ‘clan GH-A’ catalytic (β/α)8 domain and a 12-stranded beta sandwich with a jelly-roll topology.

Family Firsts

First sterochemistry determination

Aspergillus niger and Aspergillus aculeatus alpha-L-arabinfuranosidases carried out in the presence of 2.5 M methanol and followed by 1H-NMR spectroscopy [6].

First catalytic nucleophile identification

Cite some reference here, with a short (1-2 sentence) explanation [5].

First general acid/base residue identification

Cite some reference here, with a short (1-2 sentence) explanation [3].

First 3-D structure

Cite some reference here, with a short (1-2 sentence) explanation [4].

References

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

10. Hövel K, Shallom D, Niefind K, Belakhov V, Shoham G, Baasov T, Shoham Y, and Schomburg D. (2003). Crystal structure and snapshots along the reaction pathway of a family 51 alpha-L-arabinofuranosidase. EMBO J. 2003;22(19):4922-32. DOI:10.1093/emboj/cdg494 |