Importance of Lipopolysaccharide and Cyclic β-1,2-Glucans in Brucella-Mammalian Infections

Figure 2

Diagrammatic representation of the Brucella cell envelope. The cell envelope is comprised of an inner membrane, consisting of a bilayer of phospholipids, and an outer membrane with an inner leaflet of phospholipids and an outer leaflet of lipopolysaccharide (LPS). LPS consists of three components. The O-antigen faces the extracellular space and it is the component that is recognized by the adaptive immune response. The O-antigen is connected to a sugar core molecule composed of different sugars which have not yet been fully identified. Lipid A forms the hydrophobic anchor of LPS within the membrane and has a backbone of diaminoglucose, which is acylated with saturated and hydroxylated fatty acids. Brucella lipid A contains an unusual very-long-chain fatty acid (VLCFA). Cyclic β-1,2-glucans are synthesized by the inner membrane protein Cgs and then transported to the periplasm by the predicted ABC-transporter Cgt where they are modified with on average two succinyl residues by a predicted membrane protein Cgm.