1D9V

HAEMOPHILUS INFLUENZAE FERRIC-BINDING PROTEIN APO FORM

Summary for 1D9V

• Entry DOI: 10.2210/pdb1d9v/pdb
• Related: 1mrp
• Descriptor: PROTEIN (iron-utilization periplasmic protein), PHOSPHATE ION (3 entities in total)
• Functional Keywords: ferric, binding protein, iron, apo form, periplasmic protein, abc cassette receptor protein, metal binding protein
• Biological source: Haemophilus influenzae
• Total number of polymer chains: 1
• Total formula weight: 33864.22

Authors

McRee, D.E.,Bruns, C.M.,Williams, P.A. (deposition date: 1999-10-30, release date: 1999-11-17, Last modification date: 2024-02-07)

Primary citation

Bruns, C.M.,Anderson, D.S.,Vaughan, K.G.,Williams, P.A.,Nowalk, A.J.,McRee, D.E.,Mietzner, T.A.
Crystallographic and biochemical analyses of the metal-free Haemophilus influenzae Fe3+-binding protein.
Biochemistry, 40:15631-15637, 2001

PubMed Abstract: The crystal structure of the iron-free (apo) form of the Haemophilus influenzae Fe(3+)-binding protein (hFbp) has been determined to 1.75 A resolution. Information from this structure complements that derived from the holo structure with respect to the delineation of the process of iron binding and release. A 21 degrees rotation separates the two structural domains when the apo form is compared with the holo conformer, indicating that upon release of iron, the protein undergoes a change in conformation by bending about the central beta-sheet hinge. A surprising finding in the apo-hFbp structure was that the ternary binding site anion, observed in the crystals as phosphate, remained bound. In solution, apo-hFbp bound phosphate with an affinity K(d) of 2.3 x 10(-3) M. The presence of this ternary binding site anion appears to arrange the C-terminal iron-binding residues conducive to complementary binding to Fe(3+), while residues in the N-terminal binding domain must undergo induced fit to accommodate the Fe(3+) ligand. These observations suggest a binding process, the first step of which is the binding of a synergistic anion such as phosphate to the C-terminal domain. Next, iron binds to the preordered half-site on the C-terminal domain. Finally, the presence of iron organizes the N-terminal half-site and closes the interdomain hinge. The use of the synergistic anion and this iron binding process results in an extremely high affinity of the Fe(3+)-binding proteins for Fe(3+) (nFbp K'(eff) = 2.4 x 10(18) M(-1)). This high-affinity ligand binding process is unique among the family of bacterial periplasmic binding proteins and has interesting implications in the mechanism of iron removal from the Fe(3+)-binding proteins during FbpABC-mediated iron transport across the cytoplasmic membrane.

PubMed: 11747438
DOI: 10.1021/bi0156759

Experimental method

X-RAY DIFFRACTION (1.75 Å)