Insight into the specificity of Wzx for O-antigen processing
Most Gram-negative bacteria have an O antigen that consists of repeats of 3-6 sugars, and serve as an essential factor for host colonization in many disease-causing bacteria. Until now, most known O antigens are assembled by the Wzx/Wzy pathway. This involves the assembly of repeat units within the cytoplasmic face of inner membrane on a lipid carrier, undecaprenol-phosphate, which are translocated across membrane by the Wzx translocases. In the periplasmic face, the repeat units are polymerized by the Wzy polymerase, and then subsequently ligated to preformed lipid A-core in the periplasm. Earlier works have shown Wzx translocases have a relax specificity requirement over the repeat-unit structures. However, this could neither correlate to the presence of O antigen with defined structures in each respective bacteria, nor could it explain the biological diversity of Wzx translocases. Our data show that Wzx translocases have a serotype specificity over their native repeat-unit structures, and provides evidence that the earlier conclusion were obscured by protein overexpression. This provides relevant explanation to the presence of highly diverse, yet structurally defined bacterial surface polysaccharides in nature.