Glycoside Hydrolase Family 42

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• Author: ^^^Marco Moracci^^^
• Responsible Curator: ^^^Marco Moracci^^^

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Glycoside Hydrolase Family GH42
Clan	GH-A
Mechanism	retaining
Active site residues	known
CAZy DB link
http://www.cazy.org/fam/GH42.html

Substrate specificities

The best known enzymatic activity for glycoside hydrolases in this family, at the current time, is b-galactosidase (EC 3.2.1.23), however, other commonly found activities are a-L-arabinosidase (EC 3.2.1.55) and b-D-fucosidase (EC 3.2.1.38) with both K_m and k_cat in the same order of magnitude for the different substrates [1, 2]. Apparently, these enzymes show strict specificity for axial C4-OH groups.

Interestingly, Family GH42 enzymes have been identified only in unicellular organisms, mainly from prokaryotes (in majority bacteria), and with few examples from archaea and fungi. GH42 enzymes are active on lactose [2, 3, 4, 5] and transgalactosylation was also observed with production of galactooligosaccharides [6]. However, several GH42 enzymes are extracted from diverse habitats where lactose would not be present and they are very active on galactooligosaccharides and galactans [1, 7, 8, 9], suggested that these enzymes would be involved in vivo in plant degradation. This function would be performed in cooperation with family GH53 galactanases, often encoded from genes adjacent to GH42 genes [9], and with cellulosome [1].

However, the activity of GH42 enzymes on lactose and also lactulose [2] has interesting applicative potential for the removal of the former from dairy products and to monitor lactulose concentration during heat treatment leading to UHT milk.

This is an example of how to make references to a journal article [1]. (See the References section below). Multiple references can go in the same place like this [3, 4]. You can even cite books using just the ISBN [5]. References that are not in PubMed can be typed in by hand [6].

Kinetics and Mechanism

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Catalytic Residues

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Three-dimensional structures

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Family Firsts

First sterochemistry determination

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

First catalytic nucleophile identification

Cite some reference here, with a short (1-2 sentence) explanation [6].

First general acid/base residue identification

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

First 3-D structure

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

References

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15. Hidaka M, Fushinobu S, Ohtsu N, Motoshima H, Matsuzawa H, Shoun H, and Wakagi T. (2002). Trimeric crystal structure of the glycoside hydrolase family 42 beta-galactosidase from Thermus thermophilus A4 and the structure of its complex with galactose. J Mol Biol. 2002;322(1):79-91. DOI:10.1016/s0022-2836(02)00746-5 |

[[Category:Glycoside Hydrolase Families|GHnnn]]