FIGURE 8.

Proposed model for SL-1 biosynthesis and transmembrane transport. The data are most consistent with a model in which Chp1 completes SL-1 biosynthesis in the cytosolic leaflet, and MmpL8 and Sap transport SL-1 across the membrane. The membrane localization of Chp1 and the coupling of biosynthesis and transport via MmpL8 suggest that the SL-1 machinery may form a macromolecular complex to facilitate function. The mechanisms by which SL-1 is transported to the mycobacterial outer membrane are unknown. (Note that, in this figure, the hydroxyphthioceranoic groups on SL-1 are truncated.)