title: Mutational analysis of a CBM family 5 chitin-binding domain of an alkaline chitinase from Bacillus sp. J813.
abstract: Chitinase J from alkaliphilic Bacillus sp. J813 comprises a glycoside hydrolase (GH) family 18 catalytic domain (CatD), a fibronectin type III like domain, and a carbohydrate-binding module (CBM) family 5 chitin-binding domain (ChBD). It has been suggested that the ChBD binds to insoluble chitin and enhances its degradation by the CatD. To investigate the roles of two aromatic residues (Trp541 and Trp542), which are exposed on the surface of the ChBD, mutational analysis was performed. Single and double mutations of the two aromatic residues decreased binding and hydrolyzing abilities toward insoluble chitin. This result suggests that the ChBD binds to chitin by hydrophobic interactions via two surface-exposed aromatic residues. However, the double mutant, which has no such aromatic residue, bound to chitin at pH 5.2, probably by electrostatic interactions. Moreover, the ChBD bound to insoluble chitosan by electrostatic interactions.
authors.affiliation: Department of Bioengineering, Tokyo Institute of Technology, Midori-ku, Yokohama, Japan.
authors.forename: Fumiya
authors.initials: F
authors.lastname: Uni
authors.forename: Sunmi
authors.initials: S
authors.lastname: Lee
authors.forename: Rie
authors.initials: R
authors.lastname: Yatsunami
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Fukui
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nakamura
mesh_terms: D001407:Bacillus / Q000201:enzymology*; D002686:Chitin / Q000737:chemistry / Q000378:metabolism*; D002688:Chitinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004252:DNA Mutational Analysis; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D012492:Salts / Q000494:pharmacology; D012995:Solubility
chemical_list: D012492:Salts; D002686:Chitin; D002688:Chitinases