Analysis of structural features of a hrp-associated harpin from Xanthomonas axonopodis pv. citri

SGRO, G:; FICARRA, F.A.; GOTTIG, N.; JORGELINA OTTADO

Congreso; XLVIII Reunión Anual de SAIB; 2012

Phytopathogenic bacteria colonize their hosts through the secretion of effector proteins by the type III protein secretion system. This system, encoded by the hrp cluster (hypersensitive response (HR) and pathogenicity), is essential for pathogenicity in host plants and induction of HR in non-host plants. HR is a rapid response that involves cell death and slows the spread of infection. The hrp cluster of Xanthomonas axonopodis pv. citri (Xac) contains a gene that encodes a harpin protein called Hpa1. Harpins are glycine-rich heat stable proteins that can form pores in membranes and can induce HR in some plants. This sort of protein forms fibrils rich in β sheets typical of amyloid proteins. In order to study biophysically the protein Hpa1, it was expressed in Escherichia coli and purified using a size exclusion column on a FPLC equipment, showing a tetrameric structure. Using the binding to Congo Red dye assay and polarized light microscopy, it was observed the formation of amyloid-like fibrils. The kinetics of amyloid-like fibrils formation in Hpa1 under different conditions using the specific dye Thioflavin T was performed, showing a fast rate of fibrils formation. In agreement to previous results about the participation of Hpa1 in plant-pathogen interaction, this fibril structure may be involved in the elicitation of HR in non-host plants as well as in virulence in host plants.