Shigella flexneri 3a O-antigen polysaccharide

The Shigella flexneri 3a O-antigen polysaccharide is a component of lipopolysaccharide (LPS) on the outer membrane of S. flexneri serotype 3a bacteria, consisting of a repeating tetrasaccharide unit of N-acetylglucosamine-rhamnose-rhamnose-rhamnose with modifications including O-acetylation (group 6 antigen via oac gene from Sf6 phage on rhamnose III), glucosyl group (group 7,8 antigens via gtr genes from SfX phage on first rhamnose), and additional structural variations that distinguish it from the basic serotype Y backbone[1][2][4][5][6][7][12][13][15]. Biosynthesis involves sequential sugar transfer to undecaprenyl pyrophosphate (UndPP) by transferases, flipping to the periplasm via RfbX, polymerization by Rfc (chain length regulated by WzzB and others), and ligation to lipid A core by Rfa/WaaL[1][3][4]. It confers serotype-specific immunity, enhances bacterial survival by antigenic variation (often via horizontal gene transfer from phages like Sf6, SfX), promotes T3SS function through compact glycosylation, stabilizes the outer membrane, and influences motility via IcsA masking in bimodal chain lengths (short S-type and very long VL-type)[1][2][3][4][7][13]. As a key immunogen, it is targeted in multivalent conjugate vaccines against shigellosis[5][15].

Other names

S. flexneri 3a O-polysaccharideS. flexneri 3a OAgS. flexneri type 3a O-antigen

Induction of serotype-specific adaptive immunity via O-antigen epitopes Antibody-mediated neutralization of bacterial invasion