3.A.1.21.3
IrtAB of 908 aas and 6 TMSs in a 2 + 2 + 2 TMS arrangement, and 579 aas, also with 6 TMSs in a 2 + 2 + 2 TMS arrangement, respectively.  Together they form an ATC transporter with two membrane domains and two ATPase domains.  They differ from 3.A.1.21.2, being about 70% idential with respect to both the two subunits.  See IrtAB with TC# 3.A.1.21.2 for details about this transport system.  It may function together with cMBT for the import of iron-bound carboxymycobactin (cMBT) (Shankar and Akhter 2025).