Identification and Characterization of a Brucella abortus Type IV Traslocated Protein

MARCHESINI, M. I.; DIEGO JOSE COMERCI; JEAN-PIERRE GORVEL; UGALDE, R. A.

Mar del Plata

Congreso; XLIII Reunion Anual Sociedad Argentina de Investigacion en Bioquimica y Biologia Molecular; 2007

Brucella abortus is an intracellular pathogen that replicates inside mammalian phagocytic and non-phagocytic cells. A type IV secretion system (VirB) is essential to subvert lysosome fusion and to create an organelle that supports Brucella replication. Therefore, a possible role of VirB system is to translocate effector proteins that modulate host vesicular transport to allow the biogenesis of the endoplasmic reticulum-derived replicative organelle. Using the Bordetella pertussis Adenylate Cyclase reporter protein we were able to identify a B. abortus protein, called Bep1, that is translocated to the host cell via VirB system and to determine that substrate recognition involves an N-terminal translocation signal. Bep1 is a 17-kDa protein with a predicted signal peptide and a coiled-coil region that shows similarity to the autophagosomal protein atg16. VirB-mediated protein translocation into phagocytic cells was confirmed by immunofluorescence confocal microscopy. The translocated protein was localized to the phagosomal membrane from 15 minutes to 10 hours post-infection. This is consistent with the biogenesis of the replicative organelle and the expression kinetics of virB operon. Bep1 ectopically expressed in HeLa and COS-7 cells colocalized with the endoplasmic reticulum marker calreticulin, suggesting that the protein is targeting the organelle where Brucella replication occurs