Part of the ABC transporter complex IrtAB involved in the import of iron-bound mycobactin (Fe-MBT) and carboxymycobactin (Fe-cMBT) (PubMed:32296173). Has a preference for Fe-MBT over Fe-cMBT (PubMed:32296173). Transmembrane domains (TMD) form a pore in the membrane and the ATP-binding domain (NBD) is responsible for energy generation (PubMed:32296173). The ATPase activity of IrtAB is stimulated more than 38-fold in the presence of Fe-MBT, and more than 10-fold in the presence of Fe-cMBT. Forms a heterodimer with IrtA. In IrtB the ATP-binding domain (NBD) and the transmembrane domain (TMD) are fused (PubMed:32296173). The IrtAB transporter assumes an inward-facing conformation, which may represent the low-affinity state after mycobactin release towards the SID and the cytoplasm (PubMed:32296173). The import function of IrtAB is contradictory to structural predictions, which suggest that it has an ABC exporter fold. Belongs to the ABC transporter superfamily. Siderophore-Fe(3+) uptake transporter (SIUT) (TC 3.A.1.21) family.