Eukaryotic ferritin protein cages appear to be much more active in mineralization than those in prokaryotes, which could mean either a different evolutionary
path to achieve the quaternary protein cage structure, or a lag in functional studies
for prokaryotes. (See also comments in ref. Le Brun et al. 2010). In a recent surface,
where the position of iron oxo mineral precursors was monitored as the ferricinduced broadening of resonance in 13C–13C solution NMR spectra, the first two
ferrous ions oxidized (48 Fe/cage) appeared as a dimer (magnetic susceptibility)
distal to the active sites and away from the cavity surfaces (Turano et al. 2010). The
addition of saturating Fe(II) for second, third, and fourth oxidoreductase cycles
revealed the ferric oxo species moving through about 20 A ˚ channels along the long
axes of each four-helix bundle subunit to the inner edge of the protein cages. The
ferric oxo mineral precursor that is produced by the multiple catalytic sites emerged
into the cavity as multimers (mineral nuclei) of 4–8 Fe atoms. Since each subunit
channel exit is near that of three others (near the cage fourfold axes), the ferritin
protein cage of eukaryotes facilitates biomineral growth.
2.4 Ferritin Iron Biominerals
Iron biominerals in the center of ferritin protein cages of animals, plants, bacteria,
and archaea are hydrated ferric oxides. The microcrystalline materials have been
observed by electron microscopy, X-ray powder diffraction, M€ ossbauer spectroscopy, and more recently by scanning electron microscopy (SEM) (TEM)
(Rodriguez et al. 2005; Dobson 2001). Mineralized iron in ferritins varies in the
maximum number of mineralized iron atoms/cage varying from 500 in miniferritins to >4,000 in maxi-ferritins. However, in natural tissues, the average
number of mineralized iron atoms in maxi-ferritins is much less, from 800 to
Fig. 2.4 Movement iron premineral through a eukaryotic ferritin protein cage. The data are from
13C–13C solution NOESY NMR obtained after the addition of 2 Fe (II)/F ox site, for each of four
catalytic turnovers. Modified from reference 35
40
L.E. Bevers and E.C. Theil
path to achieve the quaternary protein cage structure, or a lag in functional studies
for prokaryotes. (See also comments in ref. Le Brun et al. 2010). In a recent surface,
where the position of iron oxo mineral precursors was monitored as the ferricinduced broadening of resonance in 13C–13C solution NMR spectra, the first two
ferrous ions oxidized (48 Fe/cage) appeared as a dimer (magnetic susceptibility)
distal to the active sites and away from the cavity surfaces (Turano et al. 2010). The
addition of saturating Fe(II) for second, third, and fourth oxidoreductase cycles
revealed the ferric oxo species moving through about 20 A ˚ channels along the long
axes of each four-helix bundle subunit to the inner edge of the protein cages. The
ferric oxo mineral precursor that is produced by the multiple catalytic sites emerged
into the cavity as multimers (mineral nuclei) of 4–8 Fe atoms. Since each subunit
channel exit is near that of three others (near the cage fourfold axes), the ferritin
protein cage of eukaryotes facilitates biomineral growth.
2.4 Ferritin Iron Biominerals
Iron biominerals in the center of ferritin protein cages of animals, plants, bacteria,
and archaea are hydrated ferric oxides. The microcrystalline materials have been
observed by electron microscopy, X-ray powder diffraction, M€ ossbauer spectroscopy, and more recently by scanning electron microscopy (SEM) (TEM)
(Rodriguez et al. 2005; Dobson 2001). Mineralized iron in ferritins varies in the
maximum number of mineralized iron atoms/cage varying from 500 in miniferritins to >4,000 in maxi-ferritins. However, in natural tissues, the average
number of mineralized iron atoms in maxi-ferritins is much less, from 800 to
Fig. 2.4 Movement iron premineral through a eukaryotic ferritin protein cage. The data are from
13C–13C solution NOESY NMR obtained after the addition of 2 Fe (II)/F ox site, for each of four
catalytic turnovers. Modified from reference 35
40
L.E. Bevers and E.C. Theil