IivA OF Brucella INTERACTS WITH PHOSPHOLIPIDS UNDERGOING A STRUCTURAL REARRANGEMENT

CARRICA M; CRAIG P; ALONSO S; GOLDBAUM F; SABIO Y GARCIA S; ROSSETTI O; CRAVERO S

Pinamar, Bs. As.

Congreso; 41st Annual Meeting SAIB; 2005

We have previously identified the gene iivA of Brucella as a virulence factor. It encodes an 11 kDa basic protein of unknown structure and function which is highly conserved in bacteria. The sequence analysis predicts two coiled-coil regions encompassing the C and N terminal halves. Light scattering and cross-linking experiments of complete IivA and truncated forms of the C and N terminal coiled coil regions demonstrates that the protein self-associates in solution as a trimer by its C terminal region. In this work, we demonstrate by circular dichroism (CD) that the C terminal region of IivA is helical, whereas the N terminal re- gion is mainly random coil. This result agrees with the increased susceptibility of this region to proteases as compared to the C terminal region. Phosphate anions and SDS produce a strong increa- se (40%) in the CD signal of the protein. Based on these results and the location of iivA in the genome of Brucella, we hypothesize that IivA could interact with phospholipids. In this regard, we show that IivA interacts with phosphatidic acid (PA) by Lipid Overlay Assay. Moreover, we demonstrate by CD spectra and limited proteolysis that small unilaminar vesicle made of phosphatidylcholine and PA induce conformational changes and stabilize IivA. These data contribute to understand the bases of IivA function and the intimate mechanisms of the virulence.