Plants produce a variety of pathogenesis-related (PR) proteins in response to stress or infection. The largest group of these proteins is the lytic enzymes which is composed primarily of ß,1-3 glucanases and chitinases. In their role as defense proteins these enzymes limit fungal growth by hydrolyzing (1-3)ß glucan and chitin, a ß,1-4 linked polymer of N-acetylglucosamine (GlcNAc), the major structural polysaccharides of fungal cell walls.
Barley endochitinase, a class II chitinase, is a 26 kD monomeric enzyme. It has moderate to high sequence identity with other class II plant chitinases from tobacco, potato, arabidopsis, and rice (Hart et al., 1995). The x-ray structure of barley chitinase has been solved (Hart et al., 1993) and refined to 1.8 Å resolution (Hart et al., 1995).
It has also been shown that barley chitinase is the archetypal enzyme of a superfamily of glycohydrolases which include the plant chitinases, bacterial chitosanases, and lysozymes from hen, goose and T4 phage (Monzingo et al., 1996). Despite exhibiting no significant amino acid sequence similarities, these proteins were shown to be structurally related, containing an ancient core domain which binds substrates.

Hart, P.J., Monzingo, A.F., Ready, M.P., Ernst, S.R., & Robertus, J.D. (1993) Crystal Structure of an Endochitinase from Hordeum vulgare L. Seeds J. Mol. Biol. 229, 189-193.

Hart, P.J., Pfluger, H.D., Monzingo, A.F., Hollis, T., & Robertus, J.D. (1995) The Refined Crystal Structure of an Endochitinase from Hordeum vulgare L. Seeds at 1.8 A Resolution. J. Mol. Biol. 248, 402-413.

Monzingo, A.F., Marcotte, E.M., Hart, P.J., & Robertus, J.D. (1996) Chitinases, Chitosanases, and Lysozymes can be divided into Procayotic and Eucaryotic Families Sharing a Conserved Core Nature Struc. Bio. 3, 133-140.