An oligopeptide permease, OppABCD, requires an iron-sulfur cluster domain for functionality

Oligopeptide permease, OppABCD, belongs to the type I ABC transporter family. Its role is to import oligopeptides into bacteria for nutrient uptake and to modulate the host immune response. OppABCD consists of a cluster C substrate-binding protein (SBP), OppA, membrane-spanning OppB and OppC subunits, and an ATPase, OppD, that contains two nucleotide-binding domains (NBDs). Here, using cryo-electron microscopy, we determined the high-resolution structures of Mycobacterium tuberculosis OppABCD in the resting state, oligopeptide-bound pre-translocation state, AMPPNP-bound pre-catalytic intermediate state and ATP-bound catalytic intermediate state. The structures show an assembly of a cluster C SBP with its ABC translocator and a functionally required [4Fe-4S] cluster-binding domain in OppD. Moreover, the ATP-bound OppABCD structure has an outward-occluded conformation, although no substrate was observed in the transmembrane cavity. Here, we reveal an oligopeptide recognition and translocation mechanism of OppABCD, which provides a perspective on how this and other type I ABC importers facilitate bulk substrate transfer across the lipid bilayer.