1FQF: Crystal Structures Of Mutant (k296a) That Abolish The Dilysine Interaction In The N-lobe Of Human Transferrin

Human transferrin (Tf) is responsible for the binding and transport of iron in the bloodstream of vertebrates. Delivery of this bound iron to cells occurs by a process of receptor-mediated endocytosis during which Tf releases its iron at the reduced endosomal pH of approximately 5.6. Iron release from Tf involves a large conformational change in which the two domains that enclose the binding site in each lobe move apart. We have examined the role of two lysines, Lys206 and Lys296, that form a hydrogen-bonded pair close to the N-lobe binding site of human Tf and have been proposed to form a pH-sensitive trigger for iron release. We report high-resolution crystal structures for the K206A and K296A mutants of the N-lobe half-molecule of Tf, hTf/2N, and quantitative iron release data on these mutants and the double mutant K206A/K296A. The refined crystal structures (for K206A, R = 19.6% and R(free) = 23.7%; for K296A, R= 21.2% and R(free) = 29.5%) reveal a highly conserved hydrogen bonding network in the dilysine pair region that appears to be maintained even when individual hydrogen bonding groups change. The iron release data show that the mutants retain iron to a pH 1 unit lower than the pH limit of wild type hTf/2N, and release iron much more slowly as a result of the loss of the dilysine interaction. Added chloride ions are shown to accelerate iron release close to the pH at which iron is naturally lost and the closed structure becomes destabilized, and to retard it at higher pH.
PDB ID: 1FQFDownload
MMDB ID: 15999
PDB Deposition Date: 2000/9/4
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 2.1  Å
Source Organism:
Similar Structures:
Biological Unit for 1FQF: monomeric; determined by author
Molecular Components in 1FQF
Label Count Molecule
Protein (1 molecule)
Serotransferrin(Gene symbol: TF)
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

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