The crystal structure of ferritin from Chlorobium tepidum reveals a new conformation of the 4-fold channel for this protein family

In all ferritns of known structure the short fifth E α-helix acquire an acute angle to the bundle near the C-terminus tail. However, the crystal structure of the recombinant Chlorobium tepidum ferritin (rCtFtn) shows that the presence of Arg150 in the helix E and the fact that the DE loop is formed by two amino acids produced that the helix E acquire an angle of 90° with respect the four-helical bundle. This conformation is not found in the rest of this family of proteins and defines the conformation of the 4-fold channel of rCtFtn. Despite this, the rCtFtn exhibits a cage-like hollow shell constituting of 24 monomers that are related by 4-3-2 symmetry similar to the assembly of other ferritins from eukaryotes and prokaryotes.259