Ferritin chains

TABLE 16.2 Concentration (ng mg Wet Tissue) of H- and L-Ferritin Chains in Brain Tissues (GP, SN, HP), Liver, and Heart, Determined by ELISA and Diameter (nm) of the Iron Cores Determined by Electron Microscopy [2,12]... 

The protein that stores iron in the body is called ferritin. A ferritin molecule consists of a protein coat and an iron-containing core. The outer coat is made up of 24 pol3q5eptide chains, each with about 175 amino acids. As Figure 20-27 shows, the pol q5eptides pack together to form a sphere. The sphere is hollow, and channels through the protein coat allow movement of iron in and out of the molecule. The core of the protein contains hydrated iron(HI) oxide, FC2 O3 H2 O. The protein retains its shape whether or not iron is stored on the inside. When filled to capacity, one ferritin molecule holds as many as 4500 iron atoms, but the core is only partially filled under normal conditions. In this way, the protein has the capacity to provide iron as needed for hemoglobin s mthesis or to store iron if an excess is absorbed by the body. 

Schematic representation of ferritin, the iron storage protein, (a) The protein contains 24 neariy identical polypeptides, (b) A ribbon stmcture of one of the polypeptide chains.

Table 6.1 Amino-acid sequence alignment of four mammalian ferritins (Horse L chain, HoL Human L chain, HuL Human H chain, HuH Rat H, RaH) and of one of the ferritins, FTN, and the bacterioferritin, BFR of...

Figure 6.1 Schematic representation of human isoferritins of different subunit composition. Each ferritin subunit is represented as a sausage and subunits are packed in a symmetrical shell. Twelve of the 24 subunits are visible, with H-chain subunits stippled and L-chain subunits plain. Homopolymers of H-chain and L-chain subunits are at the top and bottom of the figure respectively. The sources of various ferritins are listed in the right hand column. Reprinted from Harrison and Arosio, 1996. Copyright (1996), with permission from Elsevier Science.

This is done a contre coeur, since the L-chain sequence was the first to be established. However, it makes little sense to refer to the amino terminus of H-chain ferritins as —1, —2, etc. 

The detailed high-resolution structure of the non-haem-containing ferritin of E. coli EcFTNA has been recently published (Stillman et al, 2000) and shows considerable structural similarity to human H-chain ferritin (r.m.s. deviation of main chain... 

Several binding sites for Tb3+ or Cd2+ ions have been identified in the interior of the apoferritin protein shell, some of which may be iron-binding sites (Harrison et ai, 1989 Granier et ah, 1998). In HoSF and HoLF, two sites were identified on the inner surface of the B helix at the subunit dimer interface (Figure 6.15, Plate 11) which bind two Cd2+ ions. One involves Glu-57 and Glu-60 as ligands and the other Glu-61 and Glu-64 (Granier et al., 1998). In H-chain ferritins the first pair of Glu-57 and Glu-60 are both replaced by His and only a single Tb3+ is found bound to Glu-61 and Glu-64 (Lawson et al, 1991). 

Figure 19.1 (a) View of the 24-subunit structure of human H-chain ferritin (rHuHF) viewed down the four-fold symmetry axis, (b) The subunit of rHuHF, with the short E-helix at the top of the four-helix bundle, (c) rHuHF viewed down the three-fold symmetry axis. (From Lewin et al., 2005. Copyright with permission from The Royal Society of Chemistry, 2005.)... 

---