Structural and genetic basis for the binding of a mouse monoclonal antibody to Flavobacterium psychrophilum lipopolysaccharide

Abstract

AbstractA mouse monoclonal antibody (mAb FL100A) previously prepared against Flavobacterium psychrophilum (Fp) CSF259‐93 has now been examined for binding to lipopolysaccharides (LPS) of this strain and Fp 950106‐1/1. The corresponding O‐polysaccharides (O‐PS) of these strains are formed by identical trisaccharide repeats composed of l‐Rhamnose (l‐Rha), 2‐acetamido‐2‐deoxy‐l‐fucose (l‐FucNAc) and 2‐acetamido‐4‐R1‐2,4‐dideoxy‐d‐quinovose (d‐Qui2NAc4NR1) where R1 represents a dihydroxyhexanamido moiety. The O‐PS loci of these strains are also identical except for the gene (wzy1 or wzy2) that encodes the polysaccharide polymerase. Accordingly, adjacent O‐PS repeats are joined through d‐Qui2NAc4NR1 and l‐Rha by wzy2‐dependent α(1–2) linkages in Fp CSF259‐93 versus wzy1‐dependent β(1–3) linkages in Fp 950106‐1/1. mAb FL100A reacted strongly with Fp CSF259‐93 O‐PS and LPS but weakly or not at all with Fp 950106‐1/1 LPS and O‐PS. Importantly, it also labelled cell surface blebs on the former but not the latter strain. Additionally, mAb binding was approximately 5‐times stronger to homologous Fp CSF259‐93 LPS than to LPS from a strain with a different R‐group gene. A conformational epitope for mAb FL100A binding was suggested from molecular dynamic simulations of each O‐PS. Thus, Fp CSF259‐93 O‐PS formed a stable well‐defined compact helix in which the R1 groups were displayed in a regular pattern on the helix exterior while unreactive Fp 950106‐1/1 O‐PS adopted a flexible extended linear conformation. Taken together, the findings establish the specificity of mAb FL100A for Wzy2‐linked F. psychrophilum O‐PS and LPS.