Molecule of the Month: Ferritin and Transferrin
Ferritin and transferrin manage our essential stores of iron ions
Rich in Iron
Transporting Iron Ions
If you look through the PDB, you will find several molecules called lactoferrin and ovotransferrin that are similar to transferrin. These molecules, found in milk and egg whites respectively, also have strong binding sites for iron. However, their main function is not delivery. Instead, they serve to protect cells from bacteria. Since they mop up any free iron ions, they starve bacteria of a vital resource, slowing the growth of an infection.
Exploring the Structure
Ferritin and Iron
Three structures (PDB entry 4lqh, 4lpj, 4lyu) follow ferritin as it starts to fill with iron. The researchers soaked ferritin in a solution of iron and determined structures at different times. The one shown here was obtained after soaking for 15 minutes, and contains five iron ions bound to each subunit, coordinated by a "nanocage" of acidic and histidine amino acids. This site is also thought to be where the iron ions are converted to the safer ferric state before storage. To compare this to structures before the soak (with no iron ions), or after a one minute soak (with only one iron ion), click on the image for an interactive JSmol.
November 2002, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2002_11