Crystallization and preliminary crystallographic analysis of the ADP‐ribosyltransferase HopU1

Several Gram‐negative pathogens of plants and animals and some eukaryotic associated bacteria use type III protein‐secretion systems (T3SSs) to deliver bacterial virulence‐associated `effector' proteins directly into host cells. HopU1 is a type III effector protein from the plant pathogen Pseudomonas syringae , which causes plant bacterial speck disease. HopU1 quells host immunity through ADP‐ribosylation of GRP7 as a substrate. HopU1 has been reported as the first ADP‐ribosyltransferase virulence protein to be identified in a plant pathogen. Although several structures of ADP‐ribosyltransferases have been determined to date, no structure of an ADP‐ribosyltransferase from a plant pathogen has been determined. Here, the protein expression, purification, crystallization and preliminary crystallographic analysis of HopU1 are reported. Diffracting crystals were grown by hanging‐drop vapour diffusion using polyethylene glycol 10 000 as a precipitant. Native and SAD data sets were collected using native and selenomethionine‐derivative HopU1 crystals. The diffraction pattern of the crystal extended to 2.7 Å resolution using synchrotron radiation. The crystals belonged to space group P 4 3 , with unit‐cell parameters a = 92.6, b = 92.6, c  = 101.6 Å.