title: Functional mapping of harpin HrpZ of Pseudomonas syringae reveals the sites responsible for protein oligomerization, lipid interactions and plant defence induction.
abstract: Harpin HrpZ is one of the most abundant proteins secreted through the pathogenesis-associated type III secretion system of the plant pathogen Pseudomonas syringae. HrpZ shows membrane-binding and pore-forming activities in vitro, suggesting that it could be targeted to the host cell plasma membrane. We studied the native molecular forms of HrpZ and found that it forms dimers and higher order oligomers. Lipid binding by HrpZ was tested with 15 different membrane lipids, with HrpZ interacting only with phosphatidic acid. Pore formation by HrpZ in artificial lipid vesicles was found to be dependent on the presence of phosphatidic acid. In addition, HrpZ was able to form pores in vesicles prepared from Arabidopsis thaliana plasma membrane, providing evidence for the suggested target of HrpZ in the host. To map the functions associated with HrpZ, we constructed a comprehensive series of deletions in the hrpZ gene derived from P. syringae pv. phaseolicola, and studied the mutant proteins. We found that oligomerization is mainly mediated by a region near the C-terminus of the protein, and that the same region is also essential for membrane pore formation. Phosphatidic acid binding seems to be mediated by two regions separate in the primary structure. Tobacco, a nonhost plant, recognizes, as a defence elicitor, a 24-amino-acid HrpZ fragment which resides in the region indispensable for the oligomerization and pore formation functions of HrpZ.
authors.affiliation: General Microbiology, Department of Biological and Environmental Sciences, FI-00014 University of Helsinki, Helsinki, Finland. Minna.Haapalainen@helsinki.fi
authors.forename: Minna
authors.initials: M
authors.lastname: Haapalainen
authors.forename: Stefan
authors.initials: S
authors.lastname: Engelhardt
authors.forename: Isabell
authors.initials: I
authors.lastname: Küfner
authors.forename: Chun-Mei
authors.initials: CM
authors.lastname: Li
authors.forename: Thorsten
authors.initials: T
authors.lastname: Nürnberger
authors.forename: Justin
authors.initials: J
authors.lastname: Lee
authors.forename: Martin
authors.initials: M
authors.lastname: Romantschuk
authors.forename: Suvi
authors.initials: S
authors.lastname: Taira
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D050356:Lipid Metabolism; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010712:Phosphatidic Acids / Q000378:metabolism; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D044224:Pseudomonas syringae / Q000378:metabolism*; D017384:Sequence Deletion / Q000235:genetics; D013329:Structure-Activity Relationship; D014026:Nicotiana / Q000276:immunology* / Q000382:microbiology*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D050505:Mutant Proteins; D010455:Peptides; D010712:Phosphatidic Acids; D021122:Protein Subunits; C087295:HrpZ protein, Pseudomonas syringae