High-resolution crystal structure of the LysM effector Ecp6 of the fungal tomato pathogen Cladosporium fulvum

PR4.81 High-resolution crystal structure of the LysM effector Ecp6 of the fungal tomato pathogen Cladosporium fulvum Andrea Sanchez-Vallet [1] Raspudin Saleem Batcha [2] Anja Kombrink [1] Dirk-Jan Valkenburg [1] Jeroen R. Mesters [2] Bart P.H.J. Thomma [1] 1. Laboratory of Phytopathology, Wageningen University, 6708 PB Wageningen, Netherlands .2. Institute of Biochemistry, University of Lübeck, D-23538 Lübeck, Germany. Plants induce defence responses upon recognition of chitin, the primary structural component of fungal cell walls. To prevent the induction of host defense responses, the plant pathogenic fungus Cladosporium fulvum secretes large amounts of ECP6 protein which binds chitin with high affinity and thus prevents their recognition by plant receptors. ECP6 is a Lysin motif (LysM)-containing effector protein with orthologs, known as LysM effectors, that are widely distributed in the fungal kingdom. LysM effectors of the Septoria tritici blotch pathogen Mycosphaerella graminicola and the rice blast pathogen Magnaporthe oryzae scavenge chitin molecules in a similar fashion as C. fulvum ECP6, demonstrating the importance of LysM effectors in fungal pathogenicity. LysM domains are highly conserved in many proteins produced by prokaryotes and eukaryotes which bind to peptidoglycan and chitin. However, the specific interactions of LysM domains with their substrates have not yet been elucidated. Here, we present a high-resolution crystal structure of the LysM effector ECP6. The structure revealed that each of the three LysM domains from ECP6 adopts an aßßa tertiary structure, in which the chitin-recognition site is localized in the highly conserved region in the loop between the first ß-sheet and the first a-helix. The close interaction that occurs between the first and the third LysM domain of an Ecp6 monomer forms a high-affinity binding site for single chitin molecule.