Involved in the final steps of the cell wall sulfolipid-1 (SL-1) biosynthesis. Catalyzes two successive acylations of the precursor 2-palmitoyl-3-(C43)-phthioceranyl-alpha, alpha'-D-trehalose-2'-sulfate (SL1278) to yield the tetraacylated sulfolipid SL-1. 3 3'-(hydroxy)phthioceranyl-2'-palmitoyl(stearoyl)-2-O-sulfo-alpha,alpha-trehalose = 3,6,6'-tris-(hydroxy)phthioceranyl-2-palmitoyl(stearoyl)-2'-sulfo-alpha-alpha-trehalose + 2 2'-palmitoyl/stearoyl-2-O-sulfo-alpha,alpha-trehalose. Activity is potentiated by the SL-1 transporter MmpL8. Inhibited by the lipase inhibitor tetrahydrolipstatin (THL). The catalytic site is on the cytoplasmic side of the inner membrane. Inactivation of the mmpL8 gene interrupts the normal biosynthesis of SL-1 and leads to the accumulation of the precursor SL1278. Belongs to the mycobacterial PPE family.