PDBsum entry 5y2c

Hydrolase

PDB id: 5y2c

Contents

Protein chains

383 a.a.

Ligands

NAG-NAG-NAG-NAG-NAG ×2

NAG-NAG-MAN-MAN-MAN-MAN ×2

Waters ×243

References listed in PDB file

Key reference

• Title: Structural analysis of group ii chitinase (chtii) catalysis completes the puzzle of chitin hydrolysis in insects.
• Authors: W.Chen, M.Qu, Y.Zhou, Q.Yang.
• Ref.: J Biol Chem, 2018, 293, 2652-2660.
• PubMed id: 29317504

Abstract

Chitin is a linear homopolymer ofN-acetyl-β-d-glucosamines and a major structural component of insect cuticles. Chitin hydrolysis involves glycoside hydrolase family 18 (GH18) chitinases. In insects, chitin hydrolysis is essential for periodic shedding of the old cuticle ecdysis and proceeds via a pathway different from that in the well studied bacterial chitinolytic system. Group II chitinase (ChtII) is a widespread chitinolytic enzyme in insects and contains the greatest number of catalytic domains and chitin-binding domains among chitinases. In Lepidopterans, ChtII and two other chitinases, ChtI and Chi-h, are essential for chitin hydrolysis. Although ChtI and Chi-h have been well studied, the role of ChtII remains elusive. Here, we investigated the structure and enzymology ofOfChtII, a ChtII derived from the insect pestOstrinia furnacalisWe present the crystal structures of two catalytically active domains ofOfChtII,OfChtII-C1 andOfChtII-C2, both in unliganded form and complexed with chitooligosaccharide substrates. We found thatOfChtII-C1 andOfChtII-C2 both possess long, deep substrate-binding clefts with endochitinase activities.OfChtII exhibited structural characteristics within the substrate-binding cleft similar to those inOfChi-h andOfChtI. However,OfChtII lacked structural elements favoring substrate binding beyond the active sites, including an extra wall structure present inOfChi-h. Nevertheless, the numerous domains inOfChtII may compensate for this difference; a truncation containing one catalytic domain and three chitin-binding modules (OfChtII-B4C1) displayed activity toward insoluble polymeric substrates that was higher than those ofOfChi-h andOfChtI. Our observations provide the last piece of the puzzle of chitin hydrolysis in insects.