Fig. 1.

Pathways of SL-1 and PDIM biosynthesis. (A) The structure of SL₁₂₇₈ (4, 5) and SL-1 as proposed by Goren (33) is shown. The trehalose-2-sulfate core is esterified with two hydroxy-phthioceranic groups, one phthioceranic group and a palmitate or stearate. (B) The structures of phthiocerol, mycocerosic acids and PDIM are shown. Pps, phthiocerol synthase; Mas, mycocerosic acid synthase. PDIM consists of two mycocerosic acids esterified to phthiocerol. Mas synthesizes the methyl branched mycocerosic acids through successive additions of MMCoA (8, 9), whereas PpsA-E synthesize phthiocerol (10). FadD26 and FadD28 are responsible for activating straight chain fatty acids for transfer to Pps and Mas, respectively (34). MmpL7 and DrrC are required for transport of PDIM to the cell wall (2, 3).