Paramagnetic NMR as a tool to structurally characterize iron-sulfur proteins

Over the last two decades, the focus of iron-sulfur protein research has shifted from elucidating the biophysical and structural properties of small electron trasfer proteins to understanding the catalytic mechanisms of enzymes containing Fe-S clusters and the biosynthetic pathways that generate FeS proteins in model organisms and humans. In this frame, paramagnetic NMR spectroscopy is an “old” spectroscopic approach that, thanks to a continuous evolution of instrumentation and methodologies, can emphasize, with high precision, subtle structural aspects.

The hyperfine interaction quenches signal intensity, prevents the detection of scalar and dipolar connectivities and the sequential assignment of protein residues around the cluster(s). Nevertheless, many experiments can be optimized and novel experiments can be designed to circumvent the problem and to revive coherences invisible in routine experiments. I will show how a synergistic approach combining NMR and DFT calculations provide a comprehensive description of the electron delocalization pathway observed in [Fe₂S₂]²⁺ containing Human Ferredoxins. This can be important to reveal and discuss subtle differences in the electronic structure that can eventually modulate the functions of this protein family.  I will also review a number of studies, which altogether enphasize the role of paramagnetic NMR spectroscopy to provide a molecular view of the biogenesis of iron-sulfur proteins, to characterize redox-associated conformational changes and to address the regulatory functions of FeS proteins.