Fig. 4: Structural insights into MaPimE: Active site, substrate interactions, and functional residues.
From: Mechanistic studies of mycobacterial glycolipid biosynthesis by the mannosyltransferase PimE
a Close-up view of the active site from the cryo-EM product-bound structure of PimE bound with products Ac1PIM5 and by-product PP. Key residues are shown as sticks. Insets: Sequence logos highlighting the conservation of active site residues involved in interactions with PP or Ac1PIM5. b Same view as (a) with residues colored according to mutational effects: red-orange for complete activity loss, yellow for reduced activity, and green for no change in activity. c, d RoseTTAFold docked models of PimE with full-length donor PPM and acceptor Ac1PIM4. Residues are colored as in (b) based on mutational effects. Hydrogen bonds are shown as black dotted lines in panels (a–d). e, f Density of PPM (e) and Ac1PIM4 (f) in CG-MD simulations with respect to PimE, with the protein backbone shown as gray lines. Regions of darker color show higher density by the lipid. Key areas of the protein are highlighted. g–i HPTLC analysis of PIMs profiles from M. smegmatis strains. Each plate compares PIMs from WT M. smegmatis mc²155, ΔpimE mutant strain, and ΔpimE complemented with WT or mutant MaPimE. Major PIM species are indicated. Yellow stars mark mutants with reduced but not abolished activity (detectable PIM6 production). Mutations causing complete loss of activity are labeled in red-orange. All experiments were independently repeated two times with similar results.
