Open AccessStructural characteristics of an insect group I chitinase, an enzyme indispensable to moulting
Author(s) -
Chen Lei,
Liu Tian,
Zhou Yong,
Chen Qi,
Shen Xu,
Yang Qing
Publication year - 2014
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s1399004713033841
Subject(s) - chitinase , chitin , hydrolase , serratia marcescens , moulting , stereochemistry , glycoside hydrolase , substrate (aquarium) , enzyme , active site , biochemistry , chemistry , biology , ecology , botany , escherichia coli , chitosan , larva , gene
Insects possess a greater number of chitinases than any other organisms. This work is the first report of unliganded and oligosaccharide‐complexed crystal structures of the insect chitinase Of ChtI from Ostrinia furnacalis , which is essential to moulting. The obtained crystal structures were solved at resolutions between 1.7 and 2.2 Å. A structural comparison with other chitinases revealed that Of ChtI contains a long substrate‐binding cleft similar to the bacterial chitinase Sm ChiB from Serratia marcescens . However, unlike the exo‐acting Sm ChiB, which has a blocked and tunnel‐like cleft, Of ChtI possesses an open and groove‐like cleft. The complexed structure of the catalytic domain of Of ChtI ( Of ChtI‐CAD) with (GlcNAc) 2/3 indicates that the reducing sugar at subsite −1 is in an energetically unfavoured `boat' conformation, a state that possibly exists just before the completion of catalysis. Because Of ChtI is known to act from nonreducing ends, (GlcNAc) 3 would be a hydrolysis product of (GlcNAc) 6 , suggesting that Of ChtI possesses an endo enzymatic activity. Furthermore, a hydrophobic plane composed of four surface‐exposed aromatic residues is adjacent to the entrance to the substrate‐binding cleft. Mutations of these residues greatly impair the chitin‐binding activity, indicating that this hydrophobic plane endows Of ChtI‐CAD with the ability to anchor chitin. This work reveals the unique structural characteristics of an insect chitinase.