Crystallographic characterization of a tri-Asp metal-binding site at the three-fold symmetry axis of LarE

Abstract

Detailed crystallographic characterization of a tri-aspartate metal-binding site previously identified on the three-fold symmetry axis of a hexameric enzyme, LarE from Lactobacillus plantarum, was conducted. By screening an array of monovalent, divalent, and trivalent metal ions, we demonstrated that this metal binding site stoichiometrically binds Ca2+, Mn2+, Fe2+/Fe3+, Co2+, Ni2+, Cu2+, Zn2+, and Cd2+, but not monovalent metal ions, Cr3+, Mg2+, Y3+, Sr2+ or Ba2+. Extensive database searches resulted in only 13 similar metal binding sites in other proteins, indicative of the rareness of tri-aspartate architectures, which allows for engineering such a selective multivalent metal ion binding site into target macromolecules for structural and biophysical characterization.