Phytoferritin
Phytoferritin is a protein composed of 24 identical subunits, each largely consisting of four alpha helices (each ~40 Å long) laying side by side. Pairs of subunits lie side-by-side in a plane, forming a rhombus; in the aggregate, the 12 rhombi form a rhombic dodecahedron, which closely resembles a sphere of diameter ( ? Å) whose surface is the thickness of the diameter of the alpha helix (~? Å). The rhombic dodecahedron has 8 vertices of 4-fold symmetry and 6 vertices of 3-fold symmetry.
Highlighting Features
The vertices of 3-fold symmetryLined with glutamate, aspartate, and serine residues, are hydrophilic pores lined with chelating groups similar to those of EDTA and HEDTA.
The function of phytoferritin, like that of ferritin found in animals and humans, is to store iron when it is plentiful or excessive and to release it when iron is physiologically deficient. Iron is stored internally as a number of ferric oxides. The endogenous chelating compound is likely to be nicotianamine, closely related to mugineic acid, which is excreted by some plant species under plant stress.
McClean, R.G., M.A. Schofield, W.F. Kean, C.V. Sommer, D.P. Robertson, Dick Toth and M. Gajdardziska-Josifovska. 2002. Botanical iron minerals: Correlation between nanocrystal structure and modes of biological self-assembly. Eur. J. Mineral. 13:1235–1242.
Seckbach, J. 1982. Ferreting out the secrets of plant ferritin–a review. J. Plant Nutr. 5:369-394.
Stephan, U.D. 2002. Intra- and intercellular iron trafficking and subcellular compartmentation within roots. Plant and Soil 241:19–25.
Weisstein, E.W. 1999-2004. “Rhombic Dodecahedron.” From MathWorld–A Wolfram Web Resource. [download the net of rhombi in pdf format and build your own polyhedron!]