Binding of the AVR4 Elicitor of Cladosporium fulvum to Chitotriose Units Is Facilitated by Positive Allosteric Protein-Protein Interactions

• Published in: The Journal of biological chemistry Vol. 279; no. 16; pp. 16786 - 16796
• Main Authors: van den Burg, Harrold A., Spronk, Christian A.E.M., Boeren, Sjef, Kennedy, Matthew A., Vissers, Johannes P.C., Vuister, Geerten W., de Wit, Pierre J.G.M., Vervoort, Jacques
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 16.04.2004; American Society for Biochemistry and Molecular Biology
• Subjects: antifungal activity; carbohydrate interactions; cf-4-mediated resistance; conformational-analysis; n-acetylglucosamine; nuclear magnetic-resonance; pathogenesis-related proteins; tobacco chitinases; urtica-dioica agglutinin; wheat-germ-agglutinin
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M312594200

The attack of fungal cell walls by plant chitinases is an important plant defense response to fungal infection. Anti-fungal activity of plant chitinases is largely restricted to chitinases that contain a noncatalytic, plant-specific chitin-binding domain (ChBD) (also called Hevein domain). Current data confirm that the race-specific elicitor AVR4 of the tomato pathogen Cladosporium fulvum can protect fungi against plant chitinases, which is based on the presence of a novel type of ChBD in AVR4 that was first identified in invertebrates. Although these two classes of ChBDs (Hevein and invertebrate) are sequentially unrelated, they share structural homology. Here, we show that the chitin-binding sites of these two classes of ChBDs have different topologies and characteristics. The KD, ΔH, and ΔS values obtained for the interaction between AVR4 and chito-oligomers are comparable with those obtained for Hevein. However, the binding site of AVR4 is larger than that of Hevein, i.e. AVR4 interacts strictly with chitotriose, whereas Hevein can also interact with the monomer N-acetylglucosamine. Moreover, binding of additional AVR4 molecules to chitin occurs through positive cooperative protein-protein interactions. By this mechanism AVR4 is likely to effectively shield chitin on the fungal cell wall, preventing the cell wall from being degraded by plant chitinases.