Bacteria iron-storage proteins

Iron is stored in these proteins in the ferric form, but is taken up as Fe2+, which is oxidized by ferroxidase sites (a more detailed account of iron incorporation into ferritins is given later in this chapter). As we point out in Chapter 13, ferritins are members of the much larger diiron protein family. After oxidation, the Fe3+ migrates to the interior cavity of the protein to form an amorphous ferric phosphate core. Whereas the ferritins in bacteria appear to fulfil the classical role of iron-storage proteins, the physiological role of bacterioferritins is less clear. In E. coli it seems unlikely that bacterioferritin plays a major role in iron storage. 

To the best of our knowledge, there is one host which conforms to the structure of an Archimedean dual. Harrison was the first to point out that the quaternary structure of ferritin, a major iron storage protein in animals, bacteria, and plants, corresponds to the structure of a rhombic dodecahedron. [45] This protein, which is approximately 12.5 nm in diameter, consists of 24 identical polypeptide subunits (Fig. 9.18), and holds up to 4500 iron atoms in the form of hydrated ferric oxide with... 

Ferrihydrite is the iron oxide with the most widespread distribution in living organisms. In the form of ferritin, an iron storage protein, it is found in all organisms from bacteria through to man (in heart, spleen and liver). It occurs in plants as phytoferritin (review by Seckback, 1982). Ferritin plays a key role in iron metabolism it maintains... 

This iron storage protein is widely distributed in many mammalian cells, and also in invertebrates, plants, fungi and a number of bacteria, where it is associated with a fe-type cytochrome. There have been considerable advances recently in the understanding of its structure and physiological function.1093 1098... 

One striking similarity between iron metabolism in animals and bacteria is that both contain ferritin (63). Bacterial ferritin, or bacfer, resembles ferritin in a number of respects (Section IV), but a key difference is that bacfer is also a 6-type cytochrome (129), cytochrome bi (126). Thus the question arises Is it primarily a cytochrome or primarily an iron storage protein This question opens up a large number of avenues of research, some of which are described in Section IV, that we believe will help define further how animal ferritin functions. One important area is that of genetic control of bacfer expression. 

Ferritin, together with haemosiderin, is the principal iron storage protein in bacteria, plants and animals. In animals, ferritins occur mainly in the spleen, liver and bone marrow. Ferritins are metalloproteins that can contain up to 23% iron. The protein constituent of apoferritin has a molecular weight of 445 kDa and consists of 24 cubicaUy arranged subunits. Apoferritin forms the core package, which contains hydrated ferric hydroxide. One ferritin molecule can bind from 2000 up to 4500 iron atoms and... 

The iron transport and storage proteins transferrin and ferritin (Figures 6 and 7) are responsible for iron homeostasis in organisms after uptake e.g. through the intestine. Ferritins are assemblies of 24 polypeptide subunits, each of which has a four-helix-bundle motif. This protein directs the oxidation of Fe(II) (ferroxidase activity), the translocation of Fe(II) and Fe(III) and the mineralization of iron in the inner core of ferritin. Structures are available from, e.g., vertebrates and bacteria. The latter have two forms of ferritin, one related to the vertebrate structures discussed above, the other comprising iron mainly in the form of heme in addition, there is a dinuclear metal-binding site denoted the ferroxidase site, where the iron binds for oxidation. 

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