Department of Chemistry and Biochemistry, University of Texas, Austin 78712.
Higher plants contain multiple constitutively expressed proteins for defense against infection by viruses, bacteria, and fungi. One such class of proteins, the chitinases, are effective antifungal agents because they hydrolyze the insoluble beta-1,4-linked polymer of N-acetylglucosamine (chitin), which is the major component of the mycelial cell wall of many fungi. We report here the three-dimensional, 2.8 A, crystal structure of a 26 kDa endochitinase from barley (Hordeum vulgare L.) seeds. The 243 amino acid residue molecule is rich in alpha-helices and has three disulfide bonds. A prominent elongated cleft runs the length of the molecule, and is presumably the region responsible for substrate binding and catalysis. Endochitinases from various species of plants show a high degree of similarity in their amino acid sequences. It is therefore likely that the barley endochitinase structure can serve as a model for other plant endochitinases and that catalytic models based on that structure will be applicable to the entire enzyme family.