The interface between subunits in the head-to-tail arrangement.

<p><b>A</b>) Human frataxin interface with residues D112, D115, D122, and D124 marked in magenta. The N-terminus is colored in pink and the different monomers within the dimer are shown in yellow (head) and green (tail). A crystal structure (PDB entry 1EKG) was used for preparing the figure. <b>B</b>) CyaY interface and the residues making up the potential metal binding sites are shown. Residues H7, E19, D22, and D23, which may build up the first metal binding site, are shown as red sticks; D3, H58, and D25 may participate in the second site (yellow sticks); and H70, D29, and E44 (blue sticks) in the third. Gray spheres show Europium ions bound in the 2P1X crystal structure. Residues involved in metal binding in the crystal structures of CyaY in complex with Co and/or Eu are labeled. The different monomers in the dimer are shown in green (head) and blue (tail). Crystal structures (PDB entry 2P1X, 2EFF, and 1EW4) were used in the preparation of the figue.</p