Figure 5.

A putative working transport model. In the absence of ATP, IrtAB adopts an inward-facing conformation, but has a low-affinity binding pocket. ATP binding is associated with a transition into an occluded conformation, and subsequent formation of a hypothetical nucleotide-bound outward-facing conformation to allow substrates to bind. ATP hydrolysis opens the cytoplasmic gate. Fe³⁺-cMBT could be directly released into the cytoplasm or transferred into the SID of IrtA for the reduction and release of iron. Fe³⁺-MBT could be transferred into SID, while the lipid tail of MBT is embedded in the leaflet of the cytoplasmic side. After ADP release, IrtAB reverts back to the resting state for the next round of transport.