Glycoside Hydrolase Family 26

Substrate specificities

This family consists primarily of endo-beta1,4-mannanases, although a recent exo-acting beta- mannanase has been described. The family also contains enzymes that display beta-1,3:1,4-glucanase [1] and beta-1,3 xylanase activities.

Kinetics and Mechanism

Family GH26 enzymes are “retainers”, as shown by NMR and follow a classical Koshland double-displacement mechanism. Pre-steady state kinetics using activated substrates revealed the two phases of the reaction; the rapid initial glycosylation step (only with good leaving groups) followed by the slower deglycosylation. It should be noted that the use of substrates with a good leaving group result in a very low apparent KM, particularly with the acid-base mutant. This does not reflect tight affinity but simply that the glycosylation step (k2) is much quicker than the deglycosylation step (k3) {Bolam, 1996 #7}.

Family Firsts

First sterochemistry determination

Cite some reference here, with a short explanation [1].

First catalytic nucleophile identification

First general acid/base residue identification

First 3-D structure

References

1. 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 |
2. Araki T, Hashikawa S, and Morishita T. (2000). Cloning, sequencing, and expression in Escherichia coli of the new gene encoding beta-1,3-xylanase from a marine bacterium, Vibrio sp. strain XY-214. Appl Environ Microbiol. 2000;66(4):1741-3. DOI:10.1128/AEM.66.4.1741-1743.2000 |