“Anion clamp” allows flexible protein to impose coordination geometry on metal ions

Abstract

X-ray crystal structures of human serum transferrin (77 kDa) with Yb^III or Fe^III bound to the C-lobe and malonate as the synergistic anion show that the large Yb^III ion causes the expansion of the metal binding pocket while octahedral metal coordination geometry is preserved, an unusual geometry for a lanthanide ion.