Ferritin couples iron and fatty acid metabolism

Abstract

A physiological relationship between iron, oxidative injury, and fatty acid metabolism exists, but transduction mechanisms are unclear. We propose that the iron storage protein ferritin contains fatty acid binding sites whose occupancy modulates iron uptake and release. Using isothermal microcalorimetry, we found that arachidonic acid binds ferritin specifically and with 60 μM affinity. Arachidonate binding by ferritin enhanced iron mineralization, decreased iron release, and protected the fatty acid from oxidation. Cocrystals of arachidonic acid and horse spleen apoferritin diffracted to 2.18 Å and revealed specific binding to the 2-fold intersubunit pocket. This pocket shields most of the fatty acid and its double bonds from solvent but allows the arachidonate tail to project well into the ferrihydrite mineralization site on the ferritin L-subunit, a structural feature that we implicate in the effects on mineralization by demonstrating that the much shorter saturated fatty acid, caprylate, has no significant effects on mineralization. These combined effects of arachidonate binding by ferritin are expected to lower both intracellular free iron and free arachidonate, thereby providing a previously unrecognized mechanism for limiting lipid peroxidation, free radical damage, and proinflammatory cascades during times of cellular stress.

Ferritin iron uptake and release in the presence of metals and metalloproteins: Chemical implications in the brain

“…Arachidonic acid (ARA) is one of the most abundant fatty acids in the brain and its disturbed metabolism may be associated with neurological disorders such as AD and bipolar disorder [144]. Interestingly, Bu et al [145] recently reported a 60 µM affinity specific binding site of ferritin for ARA. Also, they described that its binding enhances iron mineralization and decreases iron release at the same time that protects the fatty acid from oxidation.…”

Discovery of a Novel General Anesthetic Chemotype Using High-throughput Screening

“…Important electrostatic contacts such as hydrogen bonding, are not represented in this binding site. Given our recent finding that the appoferritin “anesthetic site” is a fatty-acid binding site, 26 the apoferritin qHTS may prove to be a useful screening tool for finding fatty acid receptor or enzyme ligands. Additionally, the lack of GABA A R specificity could be considered an asset in finding anesthetic chemotypes that engage entirely novel anesthetic target, as may have occurred here.…”

Unsaturated Long‐Chain Fatty Acids Are Preferred Ferritin Ligands That Enhance Iron Biomineralization

“…Crystallographic studies of mammalian ferritins revealed that the pockets at the interface between two‐fold axis‐related monomers are available to bind organic molecules, including protoporphyrin, anaesthetics, and fatty acids (FA) . Therefore, it has been suggested that, besides its iron‐storage function, ferritin plays a role in lipid metabolism; a hypothesis that is supported by evidence of functional coupling between iron and fatty acid metabolism .…”

“…Crystallographic studies of mammalian ferritins revealed that the pockets at the interface between two‐fold axis‐related monomers are available to bind organic molecules, including protoporphyrin, anaesthetics, and fatty acids (FA) . Therefore, it has been suggested that, besides its iron‐storage function, ferritin plays a role in lipid metabolism; a hypothesis that is supported by evidence of functional coupling between iron and fatty acid metabolism . The crystal structure of the HoSF‐arachidonate complex (PDB 4DE6) reveals that the bound ligand has a U‐shaped conformation (Figure c), characteristic of FA located in the cavity of fatty acid binding proteins, and is close to residues E56, E57 and E60, which form the mineral nucleation site, as recently demonstrated for human homopolymeric l ‐ferritin .…”

“…Therefore, it has been suggested that, besides its iron‐storage function, ferritin plays a role in lipid metabolism; a hypothesis that is supported by evidence of functional coupling between iron and fatty acid metabolism . The crystal structure of the HoSF‐arachidonate complex (PDB 4DE6) reveals that the bound ligand has a U‐shaped conformation (Figure c), characteristic of FA located in the cavity of fatty acid binding proteins, and is close to residues E56, E57 and E60, which form the mineral nucleation site, as recently demonstrated for human homopolymeric l ‐ferritin . Interestingly, ferritin‐bound arachidonate appeared to contribute to ferrihydrite mineralization by accelerating iron uptake …”