| The type III secretion system plays a vital role for the virulence of Gram-negative bacteria [8]. Gamma-proteobacterial plant pathogens utilize type III secretion to transport cytosolic effector proteins across the cell wall of its target host cell [24]. This essential cytosol-to-cytosol interaction is accomplished through the assembly of the type III secretion apparatus (TTSA). The TTSA in proteobacterial plant pathogens is comprised of a membrane-embedded base and a hollow extracellular filament termed the Hrp pilus [16]. The base features a complex basal body that spans the periplasm and is associated with both the inner and outer membranes (of the Gram-negative bacteria) [28]. The Hrp pilus elongates through addition of protein monomers (pilins) in helical repeat at its tip, to invade the plant host cell and serve as a conduit for transport of effector proteins [24]. The pilus is considered an attractive pharmaceutical target, both because it is extracellular and because its elimination renders the bacteria non-virulent.; This work focuses on determining the structure and biophysical properties of two unrelated HrpA pilins from proteobacterial plant pathogens, Erwinia amylovora and Pseudomonas syringae. |
