Chitin-binding domain of chitinase (ChBD2)
Pyrococcus furiosus (thermophilic archaea)
Chitinase [EC 184.108.40.206] is an enzyme that can hydrolyze the β-1,4 linkage between N-acetyl-D-glucosamine (NAG) in chitin, and expected to be useful for the industrial utilization of chitin. Chitin, an insoluble, linear β-1,4-linked polymer of NAG, is a common constituent of fungal cell-walls, the exoskeletons of insects and the shells of crustaceans, being the second most abundant polysaccharide in biomass. NAG and the oligosaccharides derived from chitin are useful as food additives and medicines. Originally, the chitinase gene of Pyrococcus furiosus exists as a pseudo-gene on the genome due to a frame shift mutation. By artificially correct the frame shift, the hydrolyzing activity as the chitinase was recovered.
This artificial chitinase (Pf-Chitinase) is a thermostable enzyme, composed of two catalytic domains and two chitin-binding domains (ChBDs). One of the two chitin-binding domains (ChBD2) of Pf-Chitinase strongly binds to insoluble chitin, helping the hydrolyzing efficiency of its catalytic domain. ChBD2 belongs to the carbohydrate-binding module family 2. Since the domains in this family are diverse in their substrate specificities, the addition of the structural information will contribute to revealing the mechanisms of carbohydrate recognition.
The structure of ChBD2, which consists of two four-stranded beta-sheets, comprised a typical beta-sandwich architecture, being similar to those of the other proteins in the carbohydrate-binding module 2 family. The chitin-binding surface is flat, containing a strip of three solvent-exposed Trp residues flanked by the acidic residues. The hydrophobic interaction is dominant for the recognition of crystalline chitin, and the acidic residues are responsible for a higher substrate specificity of ChBD2 for chitin, compared to that for cellulose.
Protein Data Bank (PDB)
author: Koichi Uegaki