The deduced role of a chitinase containing two nonsynergistic catalytic domains

Abstract

The glycoside hydrolase family 18 chitinases degrade or alter chitin. Multiple catalytic domains in a glycoside hydrolase family 18 chitinase function synergistically during chitin degradation. Here, an insect group III chitinase from the agricultural pestOstrinia furnacalis(OfChtIII) is revealed to be an arthropod-conserved chitinase that contains two nonsynergistic GH18 domains according to its catalytic properties. Both GH18 domains are active towards single-chained chitin substrates, but are inactive towards insoluble chitin substrates. The crystal structures of each unbound GH18 domain, as well as of GH18 domains complexed with hexa-N-acetyl-chitohexaose or penta-N-acetyl-chitopentaose, suggest that the two GH18 domains possess endo-specific activities. Physiological data indicated that the developmental stage-dependent gene-expression pattern ofOfChtIII was the same as that of the chitin synthaseOfChsA but significantly different from that of the chitinaseOfChtI, which is indispensable for cuticular chitin degradation. Additionally, immunological staining indicated thatOfChtIII was co-localized withOfChsA. Thus,OfChtIII is most likely to be involved in the chitin-synthesis pathway.