X-ray solution scattering study of ferritin iron up-take and iron core in various buffer solutions

Introduction Mammalian ferritin is an intracellular iron storage protein assembled from 24 subunits forming a spherical shell of an outer diameter of ~13nm and an inner diameter of ~8nm. Its central cavity has a capacity for up to 4500 atoms of ferric iron. The iron loading by ferritin in vitro has been shown to be dependent upon the presence of a Good’s buffer and fails in the presence of phosphate. On the other hand, phosphate is also a major component of core in variable amounts. Horse spleen ferritin has a Fe:P ratio of ~10 and bacterial ferritin has contains a much higher ratio of Fe:P up to 1:1. The significance of phosphate in the core is not well-understood. In this report, we describe small-angle X-ray scattering (SAXS) study on the structures of iron core of native ferritin containing phosphate and of phosphate-free reconstituted.