Membrane fusion activity of the IivA virulence factor of Brucella abortus.

CARRICA M; CRAIG PO; ALONSO S; GOLBAUM FA; SABIO Y GARCIA J; ROSSETTI O; CRAVERO S

Rosario, Santa Fe, Argentina

Congreso; XLII Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2006

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB)

We have previously identified the ORF BAB1-1543 of Brucella abortus as contributing to its virulence. It encodes an 11 kDa basic protein of unknown structure and function, named IivA. We have shown that this protein has two structural domains: a carboxy terminal coiled coil domain through which the protein self-associates as a trimer, and a natively unfolded amino terminal domain that undergoes a structural rearrangement in the presence of phospholipid vesicles. To study IivA association to the vesicles we constructed two single-Trp mutants (IivA-L19W and IivA-S114W), that span the amino and carboxy terminal domains, respectively. We found that the fluorescence maximun of IivA-L19W shift to lower wavelength upon mixing with phosplolipid vesicles, while the IivA-S114W mutant showed no shift. These results and the structural resemblance of Iiva to viral membrane-fusion proteins prompted us to investigate its fusogenic activity. With this aim, we measured the size increment of phospholipid vesicles after addition of protein using Static and Dynamic Light Sacttering, and also  lipid membrane mixing by FRET of phospholipid derivatives. These experiments, demonstrated that Iiva has an in vitro membrane-fusion activity that is optimal at acidic pH. This activity require the full length protein as the isolated carboxyl and amino terminal domains have none or a moderate activity.