Glycoside Hydrolase Family 124

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• Author: ^^^Harry Gilbert^^^
• Responsible Curator: ^^^Harry Gilbert^^^

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Glycoside Hydrolase Family GH124
Clan	GH-x
Mechanism	retaining/inverting
Active site residues	known/not known
CAZy DB link
http://www.cazy.org/GH124.html

Substrate specificities

Family 124 consists of a small number of cellulosomal proteins. The Clostridium thermocellum enzyme CtCel124A is the only member of this family that has been characterized. The enzyme is an endo-&beta1,4-glucanase with modest activity in vitro, but acts in synergy with the major exo-cellulase from C. thermocellum and, as a discrete entity, is able to deconstruct tobacco cell walls [1].

Kinetics and Mechanism

HPLC using cellopentaose as the substrate showed that the enzyme has a single displacement inverting mechanism [1]. .

Catalytic Residues

The catalytic acid in CtCel124A was shown to be Glu96 based on the crystal structural of the enzyme and the observation that the Q96A mutation completely inactivates the cellulase [1]. The enzyme contains no candidate catalytic base and it was suggested that the nucleophilic water was activated by a Grotthus”-like mechanism [2].

Three-dimensional structures

The enzyme displays a superhelical fold in which a constellation of α-helices encircle a central helix that houses the catalytic apparatus. The catalytic acid, Glu96, is located at the C-terminus of the central helix. The substrate-binding cleft can be divided into two discrete topographical domains in which the bound cellotriose molecules display twisted and linear conformations, respectively, suggesting that the enzyme may target the interface between crystalline and disordered regions of cellulose .

Family Firsts

First stereochemistry 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 [4].

First general acid/base residue identification

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

First 3-D structure

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

References

1. Brás JL, Cartmell A, Carvalho AL, Verzé G, Bayer EA, Vazana Y, Correia MA, Prates JA, Ratnaparkhe S, Boraston AB, Romão MJ, Fontes CM, and Gilbert HJ. (2011). Structural insights into a unique cellulase fold and mechanism of cellulose hydrolysis. Proc Natl Acad Sci U S A. 2011;108(13):5237-42. DOI:10.1073/pnas.1015006108 |
2. Koivula A, Ruohonen L, Wohlfahrt G, Reinikainen T, Teeri TT, Piens K, Claeyssens M, Weber M, Vasella A, Becker D, Sinnott ML, Zou JY, Kleywegt GJ, Szardenings M, Ståhlberg J, and Jones TA. (2002). The active site of cellobiohydrolase Cel6A from Trichoderma reesei: the roles of aspartic acids D221 and D175. J Am Chem Soc. 2002;124(34):10015-24. DOI:10.1021/ja012659q |

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

6. Robert V. Stick and Spencer J. Williams. (2009) Carbohydrates. Elsevier Science.