lipooligosaccharides

Lipooligosaccharides, often abbreviated as LOS, are complex glycolipids found in the outer membrane of Gram-negative bacteria. They are structurally related to lipopolysaccharides (LPS), which are also components of the outer membrane, but LOS are characterized by a shorter, more variable oligosaccharide chain. LOS molecules play a crucial role in the interaction between bacteria and their environment, including their ability to adhere to host cells and evade the host immune system.

The general structure of LOS consists of three main parts: a lipid A moiety, a core oligosaccharide, and in some cases, a terminal structure. The lipid A is embedded in the bacterial outer membrane and anchors the LOS molecule. The core oligosaccharide is a branched chain of sugars that varies significantly between different bacterial species and even strains. This variability in the core structure is a key feature distinguishing LOS from LPS, which typically has a more conserved core. The terminal structures can include various sugar residues and can be highly modified, contributing to the diversity of LOS structures and their functions.

LOS are important virulence factors for many pathogenic bacteria. They can act as potent immunostimulants, triggering inflammatory responses in the host. However, their structural diversity also allows bacteria to evade recognition by the host immune system, for example, by mimicking host cell surface molecules or by undergoing phase variation, where the expression of certain LOS structures is switched on or off. This adaptability makes LOS a significant target for research in the development of new antimicrobial therapies and vaccines.