Lipopolysaccharide O antigen of Pseudomonas aeruginosa (O antigen (OSA or CPA, depending on the specific form))

The **Lipopolysaccharide (LPS) O antigen** of *Pseudomonas aeruginosa* is a highly variable surface-exposed polysaccharide that constitutes the distal part of the bacterium’s lipopolysaccharide layer. It plays a crucial role in virulence by protecting bacteria from host immune defenses and environmental stresses. The structure consists either of homopolymeric D-rhamnan repeats known as common polysaccharide antigen (CPA/A-band), or more commonly, heteropolymeric repeating units containing three to five distinct sugars called the O-specific antigen (OSA/B-band). The composition and length variability underlie *P. aeruginosa*’s classification into at least 20 major serotypes and numerous subtypes[2][3][4]. O antigens are synthesized via complex biosynthetic pathways involving multiple glycosyltransferases, polymerases such as Wzy, and ligases like WaaL that attach these polymers to lipid A-core oligosaccharides within the outer membrane[1][5]. This diversity results from horizontal gene transfer events and mutations within biosynthetic gene clusters[1][3]. Clinically, this molecule is significant because it serves as both a key virulence factor—enabling resistance to complement-mediated killing—and an important target for diagnostic typing schemes. While no approved therapeutics directly target this molecule yet, it remains under investigation as a candidate for carbohydrate-based antibacterial vaccines due to its immunogenicity and surface accessibility[4]. However, its high structural variability poses challenges in developing broadly protective interventions. In summary, while not a classical druggable "receptor," the LPS O-antigen is considered an important therapeutic target due to its essential roles in infection pathogenesis and potential utility in vaccine development against *Pseudomonas aeruginosa*[2][3][4].

Other names

O-specific antigen (OSA)Common polysaccharide antigen (CPA)B-band O-antigen (for heteropolymeric forms)A-band O-antigen (for homopolymeric D-rhamnan form)LPS O-antigenP. aeruginosa LPS O-antigen

Not applicable for small-molecule drugs; vaccine candidates aim to elicit an immune response against the antigen.