Date Published: January 01, 2018
Publisher: International Union of Crystallography
Author(s): Tian Liu, Weixing Zhu, Jing Wang, Yong Zhou, Yanwei Duan, Mingbo Qu, Qing Yang.
Multiple catalytic domains in one chitinase have been shown to function synergistically during chitin degradation. Here, using biochemical and structural characterization, an insect chitinase was revealed to have two nonsynergistic catalytic domains, which may be involved in chitin synthesis instead of chitin degradation.
The glycoside hydrolase family 18 (GH18) chitinases (EC 188.8.131.52) catalyze the breakdown of β-1,4-glycosidic bonds in chitin or chitooligosaccharides (Carbohydrate Active Enzymes database; http://www.cazy.org/; Lombard et al., 2014 ▸; The CAZypedia Consortium, 2017 ▸). They are widely distributed across the tree of life and play various vital roles (Adrangi & Faramarzi, 2013 ▸). For organisms in which chitin is a structural component, such as fungi, arthropods and nematodes, chitinases are used to remodel cell walls, cuticles and eggshells, respectively (Hartl et al., 2012 ▸; Zhu et al., 2016 ▸). In bacteria, chitinases are produced to degrade exogenous chitin for nutrients (Vaaje-Kolstad et al., 2013 ▸). In pathogenic protozoa, chitinase is used to facilitate transmission by disrupting the peritrophic matrix of insect pest vectors, such as mosquitos (Shahabuddin et al., 1993 ▸). In plants, chitinases play a defensive role against microbial pathogens by targeting their cell walls and mediate plant–microorganism symbiosis by modifying signal molecules in leguminous plants (Grover, 2012 ▸). In humans, two chitinases, macrophage chitotriosidase and acidic mammalian chitinase (AMCase), have been implicated in innate immunological responses to chitin-containing pathogens (Lee et al., 2011 ▸).
Here, we report the first structural characterization of a chitinase containing two nonsynergistic GH18 domains. The two GH18 domains of OfChtIII possess similar structures and substrate specificities, which differentiate them from the chitinolytic chitinase OfChtI-CAD (Zhu et al., 2008 ▸; Zhang et al., 2012 ▸; Li et al., 2015 ▸).