Structural and biochemical analysis completes the puzzle of chitin hydrolysis in insects

Abstract

Chitin is a linear homopolymer of β‐N‐acetyl‐D‐glucosamines and a major structural component of insect cuticles. Chitin hydrolysis involves glycoside hydrolase family 18 (GH18) chitinases and GH20 β‐N‐acetyl‐D‐hexosaminidases. In insects, chitin hydrolysis is essential for periodically shedding of the old cuticle ecdysis and proceeds via a pathway different from that in the well‐studied bacterial chitinolytic system. In Lepidopteran insects, the group II chitinase (ChtII) together with two other chitinases (ChtI and Chi‐h) and one GH20 β‐N‐acetyl‐D‐hexosaminidase (Hex1) are essential (Fig.1). Having revealed the acting mode and catalysis of ChtI, Chi‐h and Hex1, our lab recently elucidated the role of ChtII. ChtII is a widespread chitinolytic enzyme in insects and contains the greatest number of catalytic domains and chitin binding domains. We investigated the structure and enzymology of OfChtII, a ChtII representative derived from the insect pest Ostrinia furnacalis. OfChtII exhibit structural characteristics within the substrate‐binding cleft similar to those in OfChi‐h and OfChtI. However, it lacks structural elements favoring substrate binding beyond the active sites, including an extra wall structure present in OfChi‐h. Nevertheless, the numerous domains in OfChtII may compensate for this difference; a truncation containing one catalytic domain and three chitin binding modules (OfChtII‐B4C1) displayed higher activity toward insoluble polymeric substrates than those of OfChi‐h and OfChtI. Our observations complete the puzzle of chitin hydrolysis in insects and suggest a unique system distinguished from the bacterial ones. And based on the structural uniqueness, we have been able to develop highly efficient inhibitors against OfChi‐h, OfChtI, OfChtII and OfHex1.Support or Funding InformationThis work was supported by the Program for National Natural Science Funds for Distinguished Young Scholar (31425021), the National Natural Science Foundation of China (31402015), the National Key Research and Development Project of China (2017YFD0200502, 2017YFD0201207), the Fundamental Research Funds for the Central Universities (DUT17RC(4)13) and China Postdoctoral Science Foundation funded project (2017M611234).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.