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

Abstract

Horse-spleen apoferritin is known to crystallize in three different space groups, cubic F432, tetragonal P4212 and orthorhombic P2~212. A structure comparison of the cubic and tetragonal forms is presented here. Both crystal forms were obtained by the vapor-diffusion technique and data were collected at 2.26/~ (cubic crystal) and 2.60/~ (tetragonal crystal) resolution. Two main differences were observed between these crystal structures: (i) whereas intermolecular contacts only involve saltbridge type interactions via cadmium ions in the cubic structure, two types of interactions are observed in the tetragonal crystal (cadmium-ion-mediated salt bridges and hydrogen-bonding interactions) and (ii) cadmium ions bound in the threefold axes of ferritin molecules exhibit lower site-occupation factors in the tetragonal structure than in the cubic one.

Chemistry at the protein–mineral interface in L-ferritin assists the assembly of a functional (μ 3 -oxo)Tris[(μ 2 -peroxo)] triiron(III) cluster

“…Each ferritin subunit shows the characteristic fourhelix bundle tertiary structure completed by a fifth helix (Fig. 1A) (13,16). The protein models are almost complete, with the exception of the two initial and the three final residues of HoLf and the two starting residues in the HuLf sequence.…”

“…1B) for an efficient biomineralization was inferred by site-directed mutagenesis or chemical modifications (8,9). Nonphysiological metal ions like Cd 2+ have been observed bound to the corresponding glutamates of the above-mentioned human Glu residues in several mammalian L-ferritins (10)(11)(12)(13)(14) whereas the structure with iron of these homopolymeric L-ferritins has not yet been reported.…”

Nanoscale device architectures derived from biological assemblies: The case of tobacco mosaic virus and (apo)ferritin

“…L-apoferritin proved to be a good candidate for X-ray diffraction analysis as it can be easily crystallized by adding cadmium ions. 124) The protein has two binding sites for cadmium, consisting of aspartic acid and glutamic acid residues near the twofold symmetry axis. 38,124) At these sites, Cd 2+ can form salt bridges at a pH of approximately 6.0, which allow the formation of crystal structures (space group F432).…”

“…124) The protein has two binding sites for cadmium, consisting of aspartic acid and glutamic acid residues near the twofold symmetry axis. 38,124) At these sites, Cd 2+ can form salt bridges at a pH of approximately 6.0, which allow the formation of crystal structures (space group F432). Other ions such as Mg 2+ , Ca 2+ , Zn 2+ , and Ce 3+ can also act as salt bridges, 38,124) however, Cd 2+ is most efficient.…”

“…38,124) At these sites, Cd 2+ can form salt bridges at a pH of approximately 6.0, which allow the formation of crystal structures (space group F432). Other ions such as Mg 2+ , Ca 2+ , Zn 2+ , and Ce 3+ can also act as salt bridges, 38,124) however, Cd 2+ is most efficient. 38 Metal ions not only induce the formation of L-apoferritin protein crystals but can also build up two-dimensional (2D) arrays of L-apoferritin and NP containing ferritin.…”