Membrane topology of the Salmonella enterica serovar Typhimurium Group B O-antigen translocase Wzx


  • Editor: Klaus Hantke

Correspondence: Peter R. Reeves, School of Molecular and Microbial Biosciences (G08), University of Sydney, Sydney, NSW 2006, Australia. Tel.: +612 9351 2356; fax: +612 9351 4571; e-mail:


The O-antigen translocase, Wzx, is involved in translocation of bacterial polysaccharide repeat units across the cytoplasmic membrane, and is an unusually diverse, highly hydrophobic protein, with high numbers of predicted α-helical transmembrane segments (TMS). The Salmonella enterica serovar Typhimurium Group B O-antigen Wzx was an ideal candidate for topological study as the O-antigen gene cluster is one of only a few that have been well characterized. The topology profile prediction for this protein was determined using five programs, with different recognition parameters, which consistently predict that 12 TMS are present. A membrane topology model was constructed by analysis of lacZ and phoA gene fusions at randomly selected and targeted fusion sites within wzx. Enzyme activity of these, and full-length C-terminal fusion proteins, confirmed the 12-TMS topology for this Wzx, and also indicated that the C-terminus was located within the cytoplasm, which is consistent with the predicted topology.