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Publication Abstract from PubMed

The Pseudomonas syringae type III effector HopU1 is a mono-ADP-ribosyltransferase (mADP-RT) that is injected into plant cells by the type III protein secretion system. Inside the plant cell it suppresses immunity by modifying RNA-binding proteins including the glycine-rich RNA-binding protein GRP7. The crystal structure of HopU1 at 2.7 angstrom resolution reveals two unique protruding loops, L1 and L4 not found in other mADP-RTs. Site-directed mutagenesis demonstrates these loops are essential for substrate recognition and enzymatic activity. HopU1 ADP-ribosylates the conserved arginine 49 (R49) of GRP7 and this reduces GRP7's ability to bind RNA in vitro. In vivo, expression of GRP7 with R49 replaced with lysine does not complement the reduced immune responses of the Arabidopsis thaliana grp7-1 mutant demonstrating the importance of this residue for GRP7 function. These data provide mechanistic details how HopU1 recognizes this novel type of substrate and highlights the role of GRP7 in plant immunity.

Structure function analysis of an ADP-ribosyltransferase type III effector and its RNA-binding target in plant immunity.,Jeong BR, Lin Y, Joe A, Guo M, Korneli C, Yang H, Wang P, Yu M, Cerny RL, Staiger D, Alfano JR, Xu Y J Biol Chem. 2011 Oct 19. PMID:22013065^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.