Transferrin-Mediated Iron Transport Mechanisms

Transferrin is the principal iron-binding glycoprotein in vertebrate circulation, responsible for safe transport of ferric ions and regulation of systemic iron distribution. Each molecule comprises two lobes that undergo large pH-dependent conformational changes upon iron binding and release. In the bloodstream, diferric transferrin (holo-transferrin) binds to the transferrin receptor on the surface of iron-requiring cells. The receptor–transferrin complex is internalised through receptor-mediated endocytosis into acidic endosomes, where protonation triggers iron dissociation. The resulting apotransferrin remains receptor-bound and is recycled to the cell surface, releasing back into plasma at neutral pH. At the molecular level, carbonate anion acts synergistically with ferric iron to stabilise the binding site, and interlobe cooperativity enhances iron loading and unloading kinetics. Post-translational modifications of transferrin and polymorphisms in the transferrin receptor modulate binding affinities and can influence iron homeostasis in health and disease. Beyond iron, transferrin also binds certain non-ferric metal ions, opening avenues for metal-based therapeutics and diagnostic agents that exploit its receptor pathway.

Research from Nature Portfolio

Recent studies have applied low-energy electron holography to resolve the distinct conformations of single transferrin molecules in their iron-bound and iron-free states. By combining native electrospray ion beam deposition with high-resolution imaging, researchers have visualised nanometre-scale clefts in apotransferrin that arise upon iron release. Statistical analysis of single-molecule images reveals a distribution of open-state angles in the two lobes, underlining the intrinsic flexibility that governs iron binding and release. These findings demonstrate the feasibility of directly observing function-related conformational dynamics in individual transport proteins and provide a framework for investigating allosteric mechanisms and receptor recognition under near-physiological conditions.

Transferrin-Mediated Iron Transport Mechanisms publication trend

The graph below shows the total number of articles in transferrin-mediated iron transport mechanisms across all publications each year (not limited to Nature Index journals).

Technical terms

Transferrin: A bilobed glycoprotein that binds ferric ions and transports them in the circulation.

Holo-transferrin: The iron-loaded form of transferrin, containing two Fe3+ ions and a synergistic anion (typically carbonate).

Apo-transferrin: The iron-free form of transferrin that remains bound to its receptor until neutral pH induces dissociation.

Transferrin receptor: A cell-surface dimeric protein that recognises holo-transferrin and mediates its endocytic uptake.

Receptor-mediated endocytosis: The process by which ligand–receptor complexes are internalised into membrane-bound endosomes.

Conformational change: A reversible alteration in protein structure that affects ligand binding and release, often triggered by pH or ligand occupancy.

References

1. Imaging conformations of holo- and apo-transferrin on the single-molecule level by low-energy electron holography. Scientific Reports (2023).
2. Human transferrin: An inorganic biochemistry perspective. Coordination Chemistry Reviews (2021).
3. The synergistic binding of anions and Fe3+ by transferrin. Implications for the interlocking sites hypothesis.. Journal of Biological Chemistry (1975).
4. Exploring Serum Transferrin Regulation of Nonferric Metal Therapeutic Function and Toxicity. Inorganics (2020).
5. Ferric pyrophosphate citrate: interactions with transferrin. BioMetals (2018).