FIGURE 5.

Proposed pathway for the early steps of PIM biosynthesis in mycobacteria. The two pathways originally proposed for the biosynthesis of Ac₁PIM₂ in mycobacteria are shown. (i) PI is mannosylated to form PIM₁. PIM₁ is then mannosylated to PIM₂, which is acylated to form Ac₁PIM₂. (ii) PIM₁ is first acylated to Ac₁PIM₁ and then mannosylated to Ac₁PIM₂. Our experimental evidence indicates that although both pathways might co-exist in mycobacteria (13), the sequence of events PI → PIM₁ → PIM₂ → Ac₁PIM₂ is favored. As an important part of the literature concerning PIM studies refers to the nomenclature based on the M. tuberculosis H37Rv sequences, the Rv numbers of the proteins are also included.