Figure 6. Comparison of the symmetric metal ion binding site of EncFtn_sH and the ferritin FOC.

(A) Structural alignment of the FOC residues in a dimer of EncFtn_sH (green/blue) with a monomer of Pseudo-nitzschia multiseries ferritin (PmFtn) (PDBID: 4ITW) (orange) (Pfaffen et al., 2013). Iron ions are shown as orange spheres and a single calcium ion as a grey sphere. Residues within the FOC are conserved between EncFtn and ferritin PmFtn, with the exception of residues in the position equivalent to H65’ in the second subunit in the dimer (blue). The site in EncFtn with bound calcium is not present in other family members. (B) Secondary structure of aligned dimeric EncFtn_sH and monomeric ferritin highlighting the conserved four-helix bundle. EncFtn_sH monomers are shown in green and blue and aligned PmFtn monomer in orange as in A. (C) Cartoon of secondary structure elements in EncFtn dimer and ferritin. In the dimer of EncFtn that forms the FOC, the C-terminus of the first monomer (green) and N-terminus of the second monomer (blue) correspond to the position of the long linker between α2 and α3 in ferritin PmFtn.

DOI: http://dx.doi.org/10.7554/eLife.18972.016

Figure 6—figure supplement 1. Comparison of quaternary structure of EncFtn_sH and ferritin.

(A) Aligned FOC of EncFtn_sH and Pseudo-nitzschia multiseries ferritin (PmFtn) (Pfaffen et al., 2013). The metal binding site residues from two EncFtn_sH chains are shown in green and blue, while the PmFtn is shown in orange. Fe²⁺ in the FOC is shown as orange spheres and Ca²⁺ in EncFtn_sH is shown as a grey sphere. The two-fold symmetry axis of the EncFtn FOC is shown with a grey arrow (B) Cross-section surface view of quaternary structure of EncFtn_sH and PmFtn as aligned in (A) (dashed black box). The central channel of EncFtn_sH is spatially equivalent to the outer surface of ferritin and its outer surface corresponds to the mineralization surface within ferritin.

DOI: http://dx.doi.org/10.7554/eLife.18972.017