Helix packing and subunit conformation in horse spleen apoferritin

Abstract

An electron density map of horse spleen apoferritin at 0.28-nm (2.8 A) resolution and its preliminary interpretation have been described previously. Rigorous examination of this and newer maps at the same nominal resolution but calculated from more extensive data sets, including model building in a Richards' comparator, now allows us to report on structural features in more detail. We list inter-helical angles within and between neighbouring subunits, and describe a new short region of inter-subunit anti-parallel pleated sheet. A short section of electron density not properly accounted for in the first model has also been found. We also report on two alternative ways of connecting helical regions which account almost equally well for the observed electron density, and we assess these two alternative conformations and compare them with the conformations of other known proteins.

Evidence of new cadmium binding sites in recombinant horse L-chain ferritin by anomalous Fourier difference map calculation

“…Its fascinating ability to reversibly store and release iron ions to living cells has incited many studies. [1][2][3][4] At present, more than 50 sequences of ferritins and bacterioferritins (its iron-hemecontaining counterpart) are known, and the X-ray structures of several of them have been determined (horse spleen apoferritin, 5 variant human H-chain apoferritin, 6 E. coli bacterioferritin, 7 E. coli ferritin, 8 recombinant bullfrog red cell L-chain 9 ). These proteins show an invariance in their 3D structures: they all consist of a hollow shell assembly (ϳ430 kDa) of 24 subunits, arranged in 432 symmetry, whose inner cavity of about 80-Å diameter can host a ferrihydrite mineral core composed of up to 4,500 iron ions.…”

Amino acid sequence of horse spleen apoferritin

“…X-ray crystallographic studies have resulted in an electron density map of the apoferritin subunit at a nominal resolution of 0.28 nm [ 11 ,121. The subunit can best be described as a parallel bundle of four a-helices reminiscent of a number of other proteins (haemerythrin, cytochrome c', tobacco mosaic virus, myohaemerythrin, cytochrome b 562 [ 121) with two shorter helices situated perpendicular to them, interconnected by non-helical regions.…”

Comparison of the Structures of the Cubic and Tetragonal Forms of Horse-Spleen Apoferritin

“…bullfrog red cell (Trikha et al, 1995), horse spleen (Rice et al, 1983;Clegg, Stanfield, Bourne & Harrison, 1980) and recombinant human-H , show that these proteins only crystallize in the cubic space group F432, except for horse-spleen ferritin which also crystallizes in the orthorhombic P21212 and tetragonal P4212 space groups. These latter crystal forms were obtained a few years ago (Harrison, 1963;Hoy, Harrison & Hoare, 1974) but X-ray data were measured only to 6 ]k resolution compared to cubic crystals (2.7/~).…”