Structural highlights
Publication Abstract from PubMedChitinase-h (Chi-h) is of special interest among insect chitinases due to its exclusive distribution in lepidopteran insects and high sequence identity with bacterial and baculovirus homologs. Here OfChi-h, a Chi-h from Ostrinia furnacalis, was investigated. Crystal structures of both OfChi-h and its complex with chitoheptaose ((GlcN)7) reveal that OfChi-h possesses a long and asymmetric substrate binding cleft, which is a typical characteristics of a processive exo-chitinase. The structural comparison between OfChi-h and its bacterial homolog SmChiA uncovered two phenylalanine-to-tryptophan site variants in OfChi-h at subsites +2 and possibly -7. The F232W/F396W double mutant endowed SmChiA with higher hydrolytic activities toward insoluble substrates, such as insect cuticle, alpha-chitin, and chitin nanowhisker. An enzymatic assay demonstrated that OfChi-h outperformed OfChtI, an insect endo-chitinase, toward the insoluble substrates, but showed lower activity toward the soluble substrate ethylene glycol chitin. Furthermore, OfChi-h was found to be inhibited by N,N',N-trimethylglucosamine-N,N',N,N-tetraacetylchitotetraose (TMG-(GlcNAc)4), a substrate analog which can be degraded into TMG-(GlcNAc)1-2 Injection of TMG-(GlcNAc)4 into 5th-instar O. furnacalis larvae led to severe defects in pupation. This work provides insights into a molting-indispensable insect chitinase that is phylogenetically closer to bacterial chitinases than insect chitinases. Structure, Catalysis, and Inhibition of OfChi-h, the Lepidoptera-exclusive Insect Chitinase.,Liu T, Chen L, Zhou Y, Jiang X, Duan Y, Yang Q J Biol Chem. 2017 Feb 10;292(6):2080-2088. doi: 10.1074/jbc.M116.755330. Epub, 2017 Jan 4. PMID:28053084[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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