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). Forms a heterodimer with IrtA. In IrtB the ATP-binding domain (NBD) and the transmembrane domain (TMD) are fused. Belongs to the ABC transporter superfamily. Siderophore-Fe(3+) uptake transporter (SIUT) (TC 3.A.1.21) family.