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Title 

Amyloidogenesis of type III-dependent harpins from plant pathogenic bacteria

Authors 

J OhJ G KimE JeonC H YooJae Sun MoonS RheeI Hwang

Publisher 

American Society for Biochemistry and Molecular Biology

Issue Date 

2007

Keywords 

bacteriaplants (botany)amyloidogenesisbacterial proteinplant diseasegram negative bacteriumpathogenicityplant leafbacteria (microorganisms)bacterial outer membrane proteins

Abstract 

Harpins are heat-stable, glycine-rich type III-secreted proteins produced by plant pathogenic bacteria, which cause a hypersensitive response (HR) when infiltrated into the intercellular space of tobacco leaves; however, the biochemical mechanisms by which harpins cause plant cell death remain unclear. In this study, we determined the biochemical characteristics of HpaG, the first harpin identified from a Xanthomonas species, under plant apoplast-like conditions using electron microscopy and circular dichroism spectroscopy. We found that His6-HpaG formed biologically active spherical oligomers, protofibrils, and β-sheet-rich fibrils, whereas the null HR mutant His 6-HpaG(L50P) did not. Biochemical analysis and HR assay of various forms of HpaG demonstrated that the transition from an α-helix to β-sheet-rich fibrils is important for the biological activity of protein. The fibrillar form of His6-HpaG is an amyloid protein based on positive staining with Congo red to produce green birefringence under polarized light, increased protease resistance, and β-sheet fibril structure. Other harpins, such as HrpN from Erwinia amylovora and HrpZ from Pseudomonas syringae pv. syringae, also formed curvilinear protofibrils or fibrils under plant apoplast-like conditions, suggesting that amyloidogenesis is a common feature of harpins. Missense and deletion mutagenesis of HpaG indicated that the rate of HpaG fibril formation is modulated by a motif present in the C terminus. The plant cytotoxicity of HpaG is unique among the amyloid-forming proteins that occur in several microorganisms. Structural and morphological analogies between HpaG and disease-related amyloidogenic proteins, such as Aβ protein, suggest possible common biochemical characteristics in the induction of plant and animal cell death.

Citation 

Journal of Biological Chemistry, 282(18): 13601-13609

ISSN 

0021-9258

Link 

http://dx.doi.org/10.1074/jbc.M602576200

Appears in Collections

1. Journal Articles > Journal Articles

Registered Date

2019-05-02


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