Relaxation-based NMR assignment: Spotlights on ligand binding sites in human CISD3

CISD3 is a mitochondrial protein belonging to the NEET proteins family, bearing two [Fe₂S₂] clusters coordinated by CDGSH domains. At variance with the other proteins of the NEET family, very little is known about its structure-function relationships. NMR is the only technique to obtain information at the atomic level in solution on the residues involved in intermolecular interactions; however, in paramagnetic proteins this is limited by the broadening of signals of residues around the paramagnetic center. Tailored experiments can revive signals of the cluster surrounding; however, signals identification without specific residue assignment remains useless. Here, we show how paramagnetic relaxation can drive the signal assignment of residues in the proximity of the paramagnetic center(s). This allowed us to identify the potential key players of the biological function of the CISD3 protein.