Xanthomonas axonopodis pv. citri (Xac) is a phytopathogenic bacterium that causes citrus canker disease in most commercial citrus cultivars, resulting in significant losses worldwide. Symptoms of infected plants include canker lesions on fruits and leaves associated with progressive tree decline. Sequencing and annotation of Xac genome allowed us to initiate structural and functional studies of genes and proteins in order to elucidate the mechanisms involved in the plant-pathogen interaction. Structural studies are an important approach to get data concerning protein function. Here we describe the structural characterization of the XAC1151, a protein isolated in the two-hybrid screening experiments that interacts with the copper resistance protein CopB. Copper compounds have been used to control plant bacterial diseases and due to the appearance of copper-resistant bacterial strains the effectiveness of the process has been reduced. The hspA gene (XAC1151) from Xac encodes a protein of 158 amino acids that belongs to the small heat shock proteins (sHSPs) family. sHSP monomers are composed of a conserved a-crystallin domain, enriched of b-strands organized in a b-sheet sandwich responsible for dimer formation, the basic structural unit of many sHSPs. These proteins function as molecular chaperones by preventing protein aggregation. The recombinant protein was produced in E. coli and crystallized using the sitting-drop vapour-diffusion method in the presence of ammonium phosphate. X-ray diffraction data was collected up to 1.65Å resolution using a synchrotron radiation source. The crystal belongs to the rhombohedric space group R3 with unit cell parameters a=b=128.7Å and c=55.3Å. A molecular-replacement solution was found using the crystallographic structure of the sHSP from Triticum aestivum (PDB code 1GME) as a search model. The structure refinement is in progress.
Supported by FAPESP and CNPq.