Interaction between Histidine and Zn(II) Metal Ions over a Wide pH as Revealed by Solid-State NMR Spectroscopy and DFT Calculations

The interactions between histidine and metal species play essential roles in a wide range of important biological processes including enzymes catalysis and signal transduction. In this work, solid-state NMR techniques were employed to determine the interaction between histidine and Zn­(II) from pH 3.5 to 14. 2D homo- and heteronuclear correlation NMR experiments were utilized to extract the 1H, 13C, and 15N chemical shifts in various histidine–Zn­(II) binding complexes. Several histidine–Zn­(II) binding models were proposed on the basis of experimental results as well as DFT theoretical calculations. No direct interaction could be found between biprotonated histidine and Zn­(II) at acidic pH. At pH 7.5, one zinc ion could be hexa-coordinated with two histidine molecules on C′, Nα and deprotonated Nδ1 sites. As the pH increases to 11–14, both of the Nδ1 and Nε2 sites could be deprotonated as acceptors to be bound to either Zn­(II) or water. All of these findings give a comprehensive set of benchmark values for NMR parameters and structural geometries in variable histidine–Zn­(II) binding complexes over a wide pH range and might provide insights into the structure–property relationship of histidine–metal complexes in biological metalloproteins.