Cellulase

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Model of cellulase enzyme, produced by T. fusca, based on PDB structure 1JS4.

Cellulase refers to a class of enzymes produced chiefly by fungi, bacteria, and protozoans that catalyze the hydrolysis of cellulose. Several different kinds of cellulases are known, which differ structually and mechanistically. The EC number for this group of enzymes is E.C.3.2.1.4.

Reaction: Endohydrolysis of 1,4-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans.

Other names: Endoglucanase. Endo-1,4-beta-glucanase. Carboxymethyl cellulase. Endo-1,4-beta-D-glucanase. Beta-1,4-glucanase. Beta-1,4-endoglucan hydrolase. Celludextrinase. Avicelase.

[edit] Types and action

Three general types of cellulases based on the type of reaction catalyzed:

• Endo-cellulase breaks internal bonds to disrupt the crystalline structure of cellulose and expose individual cellulose polysaccharide chains

[edit] Exo-cellulase

cleaves 2-4 units from the ends of the exposed chains produced by endocellulase, resulting in
the tetrasaccharides or disaccharide such as cellobiose 

• Cellobiase or beta-glucosidase hydrolyses the endo-cellulase product into individual monosaccharides.

In the most familiar case of cellulase activity, the enzyme complex breaks down cellulose to beta-glucose. This type of cellulase is produced mainly by symbiotic bacteria in the ruminating chambers of herbivores. Aside from ruminants, most animals (including humans) do not produce cellulase in their bodies, and are therefore unable to use most of the energy contained in plant material. Enzymes which hydrolyze Hemicellulose are usually referred to as hemicellulase and are usually classified under cellulase in general. Enzymes that cleave lignin are occasionally classified as cellulase, but this is usually considered erroneous.

Within the above types there are also progressive (also known as processive) and non-progressive types. Progressive cellulase will continue to interact with a single polysacchaide strand, non-progressive cellulase will interact once then disengage and engage another polysacchaide strand.

[edit] Mechanism of cellulose hydrolysis

The three types of reaction catalyzed by cellulases:1. Breakage of the non-covalent interactions present in the crystalline structure of cellulose (endo-cellulase) 2. Hydrolysis of the individual cellulose fibers to break it into smaller sugars (exo-cellulase) 3. Hydrolysis of disaccharides and tetrasaccharides into glusoce (beta-glucosidase).

Mechanistic details of beta-glucosidase activity of cellulase

[edit] Uses

Cellulase is used for commercial food processing in coffee. It performs hydrolysis of cellulose during drying of beans. Cellulase is used in the fermentation of biomass into biofuels, although this process is relatively experimental at present. Cellulase is used as a treatment for Phytobezoars, a form of cellulose bezoar found in the human stomach.

[edit] Commercial production and application

Enzyme producing companies such as Dyadic International, Inc. have been using fungi to develop and manufacture cellulases in 150,000 liter industrial fermenters since 1994. With the advent of genetic engineering and genomics companies like Dyadic, Genencor and Novozymes, which use modern biological tools such as Dyadic's patented C1 Host Technology [1] to develop and manufacture large volumes of new and better performing enzyme mixtures in order to make the production of cellulosic ethanol more economical, the commercial development of cellulases has slowly taken root.

[edit] References

• Chapin III, F.S., P.A. Matson, H.A. Mooney. Principles of Terrestrial Ecosystem Ecology. Springer-Verlag New York, NY. 2002
• The Merck Manual of Diagnosis and Therapy, Chapter 24