FhuD: Difference between revisions

FhuD is atypical for periplasmic ligand binding proteins. It is 266 residues in length containing a secondary structure composed of 41% helical (13 helices; 110 residues) and 17% beta sheet (13 strands; 47 residues). It is a bilobal kidney bean shape with approximate dimensions 60 Å ´ 30 Å ´ 40 Å.(ref both) containing two domains which are connected by a 23-residue kinked α-helix. The N-terminal domain (residues 27–141) twisted fived-stranded parallel β-sheet with 3-2-1-4-5 linking topology whereas the C-terminal domain (residues 166–288) has a mixed five stranded β-sheet 3-2-1-4-5 linking topology; both are enclosed by α-helices. Between the two domains lies the shallow siderophore binding site approximate 10 Å deep (REF) which forms depression or “pocket.” This pocket is lined with hydrophobic residues which side chain residues are able to create stabilizing hydrogen bond with the accepted siderophore. This is large enough to accommodate the hydrophobic orinthyl linkers of the siderophore. Through rearrangements of the residues of the binding pocket and interactions with the iron-hydroxamate centers of the siderophore, recognition can occur with structurally diverse siderophores. The binding diversity is further increased since the siderophore backbones do not interact with the proteins.