Differentiating the roles of Mycobacterium tuberculosis substrate binding proteins, FecB and FecB2, in iron uptake
Fig 3
Structural comparison of Mtb FecB and FecB2 with highly similar structural homologs of siderophore-bound PBPs.
Ligand-binding sites for A. Mtb FecB (green, PDB ID 7UQ0), B. Mtb FecB2 (orange, PDB ID 4PM4), C. S. aureus HtsA complexed with ferric-staphyloferrin A (pink, PDB ID 3LI2), D. S. aureus SirA complexed with ferric-staphyloferrin B (white, PDB ID 3MWF), and E. B. subtilis YfiY complexed with ferric-schizokinen (wheat, PDB ID 3TNY) are shown. HtsA, SirA and YfiY are in complex with siderophores (stick representation in yellow with iron as an orange sphere), and coordinating residues are shown as stick representations. Polar interactions are highlighted between the siderophore and coordinating residues (dashed black lines). For FecB and FecB2, conserved or similar residues to HtsA, SirA and YfiY PBPs are shown. Notably, HtsA, SirA and YfiY all have a conserved arginine residue (R126, R125 and R91, respectively) that interacts with the bound siderophore, this arginine is notably absent in FecB and FecB2 with Leu163 and Ala106, respectively, in a similar location.