Solid-state NMR and EPR Spectroscopy of Mn²⁺ -Substituted ATP-Fueled Protein Engines

Paramagnetic metal ions deliver structural information both in EPR and solid-state NMR experiments, offering a profitable synergetic approach to study bio-macromolecules. We demonstrate the spectral consequences of Mg²⁺ / Mn²⁺ substitution and the resulting information contents for two different ATP:Mg²⁺ -fueled protein engines, a DnaB helicase from Helicobacter pylori active in the bacterial replisome, and the ABC transporter BmrA, a bacterial efflux pump. We show that, while EPR spectra report on metal binding and provide information on the geometry of the metal centers in the proteins, paramagnetic relaxation enhancements identified in the NMR spectra can be used to localize residues at the binding site. Protein engines are ubiquitous and the methods described herein should be applicable in a broad context.