2.A.6.5.5
Mycobacterial heme acquisition system, Rv0202c - Rv0207c. Takes up free heme and heme from hemoglobin as an iron source together with the secreted protein, Rv0203 (O53654) (Owens et al. 2013). May function with Rv0206c (MmpL3; TC#2.A.6.5.6) and Rv0202c (Tullius et al., 2011). However, see description of MmpL3 (2.A.6.5.6).  These two proteins are targets of drug action (Owens et al. 2013). A 12 TMS topology has been suggested (Belardinelli and Jackson 2017). Mycobacterial membrane protein Large 3 (MmpL3) is a promising drug target because its activity is essential and required for cell-wall biosynthesis. Several classes of MmpL3 inhibitors have been developed against Mycobacterium tuberculosis (Mtb) with potent anti-TB activity, one of which is the drug candidate SQ109. Yang et al. 2020 have determined crystal structures of MmpL3 in complex with NITD-349 and SPIRO. Both inhibitors bind deep in the central channel of the transmembrane (TM) domain and cause conformational changes to the protein. The amide nitrogen and indole nitrogen of NITD-349 and the piperidine nitrogen of SPIRO interact and clamp Asp645. Analysis of the two structures reveals that these inhibitors target the proton relay pathway to block the activity of MmpL3 (Yang et al. 2020).