Prussian Blue Ferritin

What is Ferritin?

Ferritin is a ubiquitous iron storage protein found in both prokaryotes and eukaryotes allowing cells to keep iron in a soluble and non-toxic form. Ferritin across different species has very similar architecture and function. This is in despite of variations at the primary structure level (REF 15). The 450 kDa protein shell consists of 24 subunits that can be composed of both heavy and light chains. Inside of this shell is room for an iron core composed of up to 4500 Fe (III) atoms stored as ferrihydrite phosphate (REF12-14). The goal of our project is to make use of this natural nanoparticle as both a scaffold and a reporter system.

How are we making Ferritin a Reporter?

Iron has naturally attracted attention for its ability to participate in Fenton chemistry. In this reaction iron acts as a catalyst in order to cause the disproportionation of hydrogen peroxide into oxygen-radical species (FIGURE HERE). The resulting hydroxyl radical can cause the oxidation of common horseradish peroxidase substrates such as 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) and 3,3’,5,5’-tetramethylbenzidine (TMB) to produce a colourimetric output. The standard iron core of ferritin however is not very suitable for catalyzing this process. The catalytic activity of ferritin can be increased by synthesizing ferritin with a magnetite core. The synthesis of this ”magnetoferritin” however is time consuming and is prone to disruption due to oxidation.

An alternative to increasing the catalytic activity of ferritin would be to provide the necessary ferrous ions for the Fenton chemistry via the iron complex Prussian blue. This compound could act as a surface modification agent to give the ferritin core a Prussian blue surface. Prussian blue has previously displayed high catalytic activity and is believed to act as a source of negative charge at appropriate pH levels in order to yield an affinity with positively charged peroxidase substrates such as TMB (ZHANG 2010 REFERENCE HERE).