Contact: Istituto Zooprofilattico Sperimentale dell’Abruzzo e del Molise “G. Caporale”
P3-04 A new model for the synthesis of the homopolymeric O-antigen of Brucella





Lipopolysaccharide (LPS) is the mayor outer membrane antigen in gram-negative bacteria and, in pathogens, is a central macromolecule in the pathogenic process. In Brucella the LPS has been shown to be a virulence factor required for the successful establishment of a persistent infection and that it affects the efficient intracellular replication of the bacterium, a hallmark of the infectious cycle. To date the accepted model for the synthesis of the O-antigen of Brucella fits the canonical homopolymeric pathway: the synthesis of the complete structure is completed on one poly-prenol-phosphate that is, afterwards, translocated to the periplasmic side of the inner membrane and ligated to the lipid-A-core completing the synthesis of the LPS. In this presentation we will present evidence that the synthesis of the O-antigen in Brucella occurs through a different mechanism as the one previously proposed and that it does not adjust to the canonicalhomopolymeric model. We found that Brucella uses two decaprenol-phosphate intermediaries: one onto which the perosamines and formyl- perosamines are polymerized and a second one, primed with the trisaccharide NAc-Qui-Man-Man that serves as an acceptor for the polymerized perosamines. We have additionally identified a protein with no known function to date, that controls the length of the O-antigen linked to the LPS modulating the number of perosamines polymerized on the first lipid intermediary. This mechanism of synthesis constitutes a new model for homopolymeric O-antigens.