FIGURE 1.

Biosynthesis of PIMs in mycobacteria. A, PimA transfers a Manp residue from GDP-Man to the 2-position of the myo-inositol ring of PI to form phosphatidyl-myo-inositol monomannoside (PIM₁). The reaction occurs with retention of the anomeric configuration of the sugar donor. B, schematic representation showing the crystal structures of PimA, including its apo compact, apo extended, PimA-GDP-Man, and PimA-GDP-diC8PI complexes (11, 12). The dynamic N-terminal region is shown in rainbow-colored schematic representation. C, secondary structure elements of a selected region corresponding to residues 110–170, as observed in the apo compact, apo extended, PimA-GDP-Man, and PimA-GDP-diC8PI complexes. D, location of Trp-82, Trp-154, and Trp-349 in the N-terminal Rossmann domain of the GT-B mannosyltransferase PimA. E, activity measurements showing that PimA-Trp-82, PimA-Trp-154, and PimA-Trp-349 mutant variants are functional proteins. The enzymatic activities of the three double mutants are shown as a percentage of the wild type activity. Data represent mean ± S.D. from three independent experiments.