Figure 4. Proposed mechanism of IrtAB-mediated mycobactin uptake.
IrtAB imports both Fe-MBT and Fe-cMBT across the inner membrane. For Fe-cMBT, an alternative import mechanism exists. After import, Fe-MBT remains anchored to the membrane and is thereby ideally positioned for reduction by the SID. The SID is essential for iron utilization via Fe-MBT, but not via Fe-cMBT. Iron-bound mycobactins are shown in red, desferrated mycobactins in white.