Novel Architecture of a Bacterial Plasma Membrane Transporter

Researchers used X-ray diffraction to reveal a crystal structure for an O-antigen transporter, called Wzm-Wzt, in an unexpected channel-forming conformation.

O-antigens are cell surface polysaccharides of many Gram-negative bacterial pathogens that aid in escaping the host’s innate immune responses. A widespread O-antigen biosynthesis mechanism involves the synthesis of the lipid-anchored polymer on the cytosolic face of the inner membrane, followed by transport to the periplasmic side where it is ligated to the lipid A core to complete a lipopolysaccharide molecule.

The channel-forming structure stands in contrast to the classical “altering access” mechanism typically used by this class of transporters. Such transmembrane channels are usually confined to ion channels and various toxins and are not observed in transporters that move solutes against their concentration gradient. However, the particular length of O-antigens requires the Wzm-Wzt transporter to utilize this special transport mechanism.