title: Discoidin domain of chitosanase is required for binding to the fungal cell wall.
abstract: Previously, we reported properties of a glycosylase belonging to GH-8 glycosyl hydrolase (GH) and having both chitosanase and glucanase activities. This enzyme (D2), whose molecular mass (86 kDa) was the largest among the GH-8 group, has its catalytic domain at the N-terminal region, and discoidin domain (DD) at the C-terminal region. Although various chitosanases, chitinases and glucanases have been known, DD is unique to the D2 enzyme. Glucanase and chitinase, but not chitosanase, are known to have functional domain such as carbohydrate-binding module, besides catalytic domain. Accordingly, function of the DD of D2 chitosanase was analyzed, using zygomycete cell wall containing chitosan, glucan and chitin as the basic constituents. The DD specifically and tightly bound to chitosan, but did not participate in affinity for glucan and chitin. Deletion of the DD caused marked reduction in absorbability to cell wall and in hydrolytic activity toward chitosan and glucan. These results suggest that the DD is concerned in binding of the enzyme to cell wall and in effective digestion of the insoluble substrate, through hydrolysis of not only chitosan but also coexisting glucan. Thus, this is the first example of chitosan-binding domain among various carbohydrate-binding modules reported thus far.
authors.affiliation: Department of Bioscience, Fukui Prefectural University, Fukui, Japan. kimoto@fpu.ac.jp
authors.forename: Hisashi
authors.initials: H
authors.lastname: Kimoto
authors.forename: Miho
authors.initials: M
authors.lastname: Akamatsu
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Fujii
authors.forename: Hirosuke
authors.initials: H
authors.lastname: Tatsumi
authors.forename: Hideo
authors.initials: H
authors.lastname: Kusaoke
authors.forename: Akira
authors.initials: A
authors.lastname: Taketo
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism*; D002686:Chitin / Q000378:metabolism; D048271:Chitosan / Q000378:metabolism; D005936:Glucans / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000235:genetics* / Q000378:metabolism*; D056507:Paenibacillus / Q000201:enzymology*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion
chemical_list: D001426:Bacterial Proteins; D005936:Glucans; D002686:Chitin; D048271:Chitosan; D006026:Glycoside Hydrolases; C019868:chitosanase