1d9v
From Proteopedia
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HAEMOPHILUS INFLUENZAE FERRIC-BINDING PROTEIN APO FORM
Overview
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.
About this Structure
1D9V is a Single protein structure of sequence from Haemophilus influenzae with PO4 as ligand. Full crystallographic information is available from OCA.
Reference
Crystallographic and biochemical analyses of the metal-free Haemophilus influenzae Fe3+-binding protein., Bruns CM, Anderson DS, Vaughan KG, Williams PA, Nowalk AJ, McRee DE, Mietzner TA, Biochemistry. 2001 Dec 25;40(51):15631-7. PMID:11747438
Page seeded by OCA on Tue Nov 20 13:06:46 2007
