Abstract

Brassica juncea chitinase is an endo-acting, pathogenesis-related protein that is classified into glycoside hydrolase family 19, with highest homology (50-60%) in its catalytic domain to class I plant chitinases. Here we report X-ray structures of the chitinase catalytic domain from wild-type (apo, as well as with chloride ions bound) and a Glu234Ala mutant enzyme, solved by molecular replacement and refined at 1.53, 1.8 and 1.7 angstrom resolution, respectively. Confirming our earlier mutagenesis studies, the active-site residues are identified as Glu212 and Glu234. Glu212 is believed to be the catalytic acid in the reaction, whereas Glu234 is thought to have a dual role, both activating a water molecule in its attack on the anomeric carbon, and stabilizing the charged intermediate. The molecules in the various structures differ significantly in the conformation of a number of loops that border the active-site cleft. The differences suggest an opening and closing of the enzyme during the catalytic cycle. Chitin is expected to dock first near Glu212, which will protonate it. Conformational changes then bring Glu234 closer, allowing it to assist in the following steps. These observations provide important insights into catalysis in family 19 chitinases

Published in

FEBS Journal
2007, Volume: 274, number: 14, pages: 3695-3703
Publisher: BLACKWELL PUBLISHING

SLU Authors

• Ubhayasekera, Wimal

  • Department of Molecular Biology, Swedish University of Agricultural Sciences
    

• Mowbray, Sherry

  • Department of Molecular Biology, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Food Science
Environmental Sciences related to Agriculture and Land-use
Forest Science


Publication Identifiers

DOI: https://doi.org/10.1111/j.1742-4658.2007.05906.x

Permanent link to this page (URI)

https://res.slu.se/id/publ/16955