CPK Color Scheme

On this page, you can see a Beta-1,4-Endoglucanase molecule.

Reset and spin this Beta-1,4-Endoglucanase molecule attached to a cellopentaose molecule and a cellotetraose molecule. Although this catalytic domain is sometimes complexed with a cellulose-binding domain, it can hydrolyze cellulose independently as well. The structure of the this catalytic domain model includes residues 1-434 of the 497 residues found in the mature protein.

Notice the secondary structure of this molecule. Beta sheets are gold and the alpha helices are pink. (The cellulose molecules have been removed).

Now watch as the protein folds into a large ß-sandwich surrounding the cellulose oligosaccharide.

In order to determine the mechanism behind the hydrolysis of cellulose, look at the chemical properties throughout the molecule. Polar acidic residues are red, polar basic amino acids are blue, and polar uncharged amino acids are pink.
Identify the active site within the tunnel of the protein. In the first reaction (glycosylation), a negatively charged carboxylate residue performs a nucleophilic attack on the fourth oxygen in a cellulose ring with the help of a nearby acid-catalyst in the form of a protonated carboxylate reside. The anomeric atom is inverted and is then attacked by a water molecule with the help of the now deprotonated base-catalyst carboxylate residue. The nucleophile in the first reaction acts as a leaving group and the cellulose monomer breaks free. Glu212 and Glu217 (sky blue) are thought to work together in this substitution reaction.

For questions or comments, please email Brianna Pearson

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Divne, C. Stahlberg, J., Teeri, T.T., and Jones, T.A. 2007. High-resolution crystal structures reveal how a cellulose chain is bound in the 50 A long tunnel of cellobiohydrolase 1 from Trichoderma reesei. Journal of Molecular Biology. 275(2): 309-325.