Mechanistic Insights Revealed by YbtPQ in the Occluded State

Recently, several ATP-binding cassette (ABC) importers have been found to adopt the typical fold of type IV ABC exporters. Presumably, these importers would function under the transport scheme of "alternating access" like those exporters: cycling through conformations of inward-open, occluded, and outward-open. Understanding how the exporter-like importers move substrates in the opposite direction requires structural studies in all the major conformations. To shed light on that, here we report the structure of yersiniabactin importer YbtPQ from uropathogenic Escherichia coli in the occluded conformation trapped by ADP-vanadate (ADP.Vi) at 3.1[A] resolution determined by cryo electron microscopy. The structure shows unusual local rearrangements in multiple helices and loops in its transmembrane domains (TMDs). In addition, the dimerization of nucleotide-binding domains (NBDs) promoted by the vanadate trapping is highlighted by the "screwdriver" action happening at one of the two hinge points. These structural observations are rare and thus provide valuable information to understand the structural plasticity of the exporter-like ABC importers.