Required for the biosynthesis and the transport across the inner membrane of sulfolipid-1 (SL-1), which is a major cell wall lipid of pathogenic mycobacteria. Could also transport SL1278 (2-palmitoyl-3-(C43)-phthioceranyl-alpha, alpha'-D-trehalose-2'-sulfate), which is the precursor of SL-1. Required for virulence. Up-regulated by the PhoP/PhoR two-component system. Cells show attenuated virulence in murine survival studies although initial replication rates and containment of this replication in the lung and spleen are identical to the wild-type. Inactivation of the mmpL8 gene interrupts the normal biosynthesis of SL-1 and leads to the accumulation of the precursor SL1278. Was identified as a high-confidence drug target. Belongs to the resistance-nodulation-cell division (RND) (TC 2.A.6) family. MmpL subfamily.