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Indexed by:期刊论文

Date of Publication:2014-04-01

Journal:ACTA CRYSTALLOGRAPHICA SECTION D-BIOLOGICAL CRYSTALLOGRAPHY

Included Journals:SCIE、PubMed、Scopus

Volume:70

Issue:Pt 4

Page Number:932-942

ISSN No.:1399-0047

Key Words:Ostrinia furnacalis,chitinase,glycosyl hydrolase,insects

Abstract: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 OfChtI from Ostrinia furnacalis, which is essential to moulting. The obtained crystal structures were solved at resolutions between 1.7 and 2.2 angstrom. A structural comparison with other chitinases revealed that OfChtI contains a long substrate-binding cleft similar to the bacterial chitinase SmChiB from Serratia marcescens. However, unlike the exo-acting SmChiB, which has a blocked and tunnel-like cleft, OfChtI possesses an open and groove-like cleft. The complexed structure of the catalytic domain of OfChtI (OfChtI-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 OfChtI is known to act from nonreducing ends, (GlcNAc)(3) would be a hydrolysis product of (GlcNAc)(6), suggesting that OfChtI 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 OfChtI-CAD with the ability to anchor chitin. This work reveals the unique structural characteristics of an insect chitinase.