title: Crystallographic structure of ChitA, a glycoside hydrolase family 19, plant class IV chitinase from Zea mays.
abstract: Maize ChitA chitinase is composed of a small, hevein-like domain attached to a carboxy-terminal chitinase domain. During fungal ear rot, the hevein-like domain is cleaved by secreted fungal proteases to produce truncated forms of ChitA. Here, we report a structural and biochemical characterization of truncated ChitA (ChitA ΔN), which lacks the hevein-like domain. ChitA ΔN and a mutant form (ChitA ΔN-EQ) were expressed and purified; enzyme assays showed that ChitA ΔN activity was comparable to the full-length enzyme. Mutation of Glu62 to Gln (ChitA ΔN-EQ) abolished chitinase activity without disrupting substrate binding, demonstrating that Glu62 is directly involved in catalysis. A crystal structure of ChitA ΔN-EQ provided strong support for key roles for Glu62, Arg177, and Glu165 in hydrolysis, and for Ser103 and Tyr106 in substrate binding. These findings demonstrate that the hevein-like domain is not needed for enzyme activity. Moreover, comparison of the crystal structure of this plant class IV chitinase with structures from larger class I and II enzymes suggest that class IV chitinases have evolved to accommodate shorter substrates.
authors.affiliation: Department of Biology, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1.
authors.forename: Marcia M
authors.initials: MM
authors.lastname: Chaudet
authors.forename: Todd A
authors.initials: TA
authors.lastname: Naumann
authors.forename: Neil P J
authors.initials: NP
authors.lastname: Price
authors.forename: David R
authors.initials: DR
authors.lastname: Rose
mesh_terms: D002688:Chitinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006868:Hydrolysis; D008958:Models, Molecular; D017354:Point Mutation; D011485:Protein Binding; D011487:Protein Conformation; D003313:Zea mays / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics
chemical_list: D002688:Chitinases
keywords: chitin; chitinase; crystal structure; enzyme catalysis; mass spectrometry; plant defense