Transports trehalose monomycolate (TMM) to the cell wall. Flips TMM across the inner membrane (PubMed:22252828, PubMed:22344175). Membrane potential is not required for this function. Transports probably phosphatidylethanolamine (PE) as well. Binds specifically both TMM and PE, but not trehalose dimycolate (TDM). Binds also diacylglycerol (DAG) and other phospholipids, including phosphatidylglycerol (PG), phosphatidylinositol (PI), and cardiolipin (CDL). Contributes to membrane potential, cell wall composition, antibiotic susceptibility and fitness (By similarity). Could also be part of a heme-iron acquisition system (PubMed:21383189). Is the target of the antitubercular drug SQ109. Inhibited by the antitubercular drug SQ109. Also inhibited by several other compounds such as the pyrrole derivative BM212, the adamantyl urea derivative AU1235, the benzimidazole C215, indoleamides, tetrahydropyrazolo[1,5-a]pyrimidine-3-carboxamide (THPP) and N-benzyl-6',7'-dihydrospiro[piperidine-4,4'-thieno[3,2-c]pyran] (Spiro) analogs. Inhibitory effects of these compounds, including SQ109, are most likely due to their ability to dissipate the transmembrane electrochemical proton gradient. Monomer. Interacts with TtfA (via N-terminus); active trehalose monomycolate (TMM) biosynthesis is not required for the complex formation. Colocalizes with TtfA to the cell poles and septa. Trehalose monomycolate (TMM) synthesis is not required for localization to the poles or septa. Belongs to the resistance-nodulation-cell division (RND) (TC 2.A.6) family. MmpL subfamily.