Regulation of Iron Transport

Now, regulation of all three of these proteins is very important. The cell doesn't want to have too much iron, but it also doesn't want to have too little iron. And that regulation largely focuses on the receptor and on the ferritin itself by a very interesting mechanism that I'm going to describe to you now. So, both of the mechanisms for controlling these two proteins involve an iron response element or IRE. This is a structure that appears in the messenger RNA coding for each of these two proteins. This sequence forms what's called a secondary structure that I'll show in the messenger RNA in just a second. The sequence in structure is found in the coding for both the ferritin and the transferrrin receptors and it's also found in some other iron metabolizing proteins, which tells us that again managing the proper amounts of each of these proteins is important just like managing their relative amounts of iron is important. The iron response element works by being a target for binding for a protein called the IRE binding protein. Its acronym is growing. It's called the IRE-BP. Now, the IRE-BP can either bind to IREs in the messenger RNA or it can bind to iron, but it can't bind to both. So the competition which one wins the race to binds it to the IRE-BP? The one that wins the race is the one that's the most abundant. If the iron concentration is high, the IRE-BP binds to the iron, not to the IRE. If the iron concentration is low, the IRE-BP binds to the IRE. Remember, the IRE is part of the messenger RNA. Now, as we will see, this has different effects on these two messenger RNAs. Well, rather than use words, let's go look at...