Structural characteristics of an insect group I chitinase, an enzyme indispensable to moulting.
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 Å. 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.
School of Life Science and Biotechnology, Dalian University of Technology, 2 Linggong Road, Dalian, Liaoning 116024, People's Republic of China.
Lei
L
Chen
School of Life Science and Biotechnology, Dalian University of Technology, 2 Linggong Road, Dalian, Liaoning 116024, People's Republic of China.
Tian
T
Liu
School of Software, Dalian University of Technology, 321 Tuqiang Street, Dalian, Liaoning 116620, People's Republic of China.
Yong
Y
Zhou
School of Life Science and Biotechnology, Dalian University of Technology, 2 Linggong Road, Dalian, Liaoning 116024, People's Republic of China.
Qi
Q
Chen
State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, People's Republic of China.
Xu
X
Shen
School of Life Science and Biotechnology, Dalian University of Technology, 2 Linggong Road, Dalian, Liaoning 116024, People's Republic of China.
Qing
Q
Yang
D000818:Animals; D002688:Chitinases / Q000737:chemistry* / Q000235:genetics; D007915:Lepidoptera / Q000201:enzymology*; D008958:Models, Molecular; D009154:Mutation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
D002688:Chitinases
Ostrinia furnacalis; chitinase; glycosyl hydrolase; insects