Investigation of the Expression of the O:54 antigen from Salmonella enterica
WbbF is a proposed member of the synthase family of dual glycosyltransferase-exporter proteins. WbbF assembles the O:54 antigen from Salmonella enterica. The wb*O:54 operon (encoding wbbE, wbbF and mnaA) is found on a naturally-occuring plasmid (pWQ799). Previous research suggested only WbbE and WbbF are necessary for O:54 antigen assembly due to the presence of a chromosomal gene encoding WecB, a functional homolog of MnaA. WecB and MnaA synthesize the essential UDP-ManNAc donor. However, this study determined optimal production of O:54 in E. coli was dependent on the presence of MnaA. A growth defect was observed in cells producing O:54 antigen, but unable to ligate it to the lipopolysaccharide acceptor (due to ΔwaaL). Cells recovered growth over time via mutations that turned off (or down) O:54 antigen biosynthesis. During this study, a cysteine-free version of WbbF that retained function was established, providing a key resource for future topology mapping experiments.