NMR of Paramagnetic Proteins: 13C Derived Paramagnetic Relaxation Enhancements Are an Additional Source of Structural Information in Solution

In paramagnetic metalloproteins, longitudinal relaxation rates of C-13 ' and C-13(alpha) nuclei can be measured using C-13 detected experiments and converted into electron spin-nuclear spin distance restraints, also known as Paramagnetic Relaxation Enhancement (PRE) restraints. C-13 are less sensitive to paramagnetism than H-1 nuclei, therefore, C-13 based PREs constitute an additional, non-redundant, structural information. We will discuss the complementarity of C-13 PRE restraints with H-1 PRE restraints in the case of the High Potential Iron Sulfur Protein (HiPIP) PioC, for which the NMR structure of PioC has been already solved by a combination of classical and paramagnetism-based restraints. We will show here that C-13 R-1 values can be measured also at very short distances from the paramagnetic center and that the obtained set of C-13 based restraints can be added to H-1 PREs and to other classical and paramagnetism based NMR restraints to improve quality and quantity of the NMR information.