Structural basis of host autophagy-related protein 8 (ATG8) Binding by the irish potato famine pathogen effector protein PexRD54

Abstract

Filamentous plant pathogens deliver effector proteins to host cells to promote infection. The Phytophthora infestans RXLRtype effector PexRD54 binds potato ATG8 via its ATG8 familyinteracting motif (AIM) and perturbs host-selective autophagy. However, the structural basis of this interaction remains unknown. Here, we define the crystal structure of PexRD54, which includes a modular architecture, including five tandem repeat domains, with the AIM sequence presented at the disordered C terminus. To determine the interface between PexRD54 and ATG8, we solved the crystal structure of potato ATG8CL in complex with a peptide comprising the effector's AIM sequence, and we established a model of the full-length PexRD54-ATG8CL complex using small angle x-ray scattering. Structureinformed deletion of the PexRD54 tandem domains reveals retention of ATG8CL binding in vitro and in planta. This study offers new insights into structure/function relationships of oomycete RXLR effectors and how these proteins engage with host cell targets to promote disease.