Might be involved in translocating phthiocerol dimycocerosates (PDIM) from the cell membrane to the outer membrane; PDIM forms part of the cell wall. Forms a U-shaped beta-half-barrel with a large hydrophobic cavity which is large enough to hold a single phthiocerol dimycocerosate (PDIM) molecule. Modified by Lgt on Cys-27 with an S-linked diacylglycerol with a mixture of C16 and C19 fatty acids (palmitic and tuberculostearic acid), signal peptide is removed by LspA, modified by Lnt with an amide-linked mixture of C16 and C19 fatty acids. Belongs to the LppX/LprAFG lipoprotein family.