Solid state NMR of paramagnetically labeled ubiquitin

The study of paramagnetic biomolecules is one of the fundamental challenges remaining in NMR spectroscopy. In the liquid-state, the observation of residues close to a paramagnetic center is prevented by fast nuclear relaxation in the vicinity of unpaired electrons via the Curie mechanism, a limiting factor in the study of paramagnetic proteins. On the other hand, paramagnetic effects serve as well-established restraints for molecular structure determination by solution NMR.;Paramagnetic relaxation processes in the solid are to a large extent characterized by the absence of molecular tumbling and therefore by Curie relaxation, promises longer life-times for the magnetization. This is a remarkable advantage for solid state NMR spectroscopy in probing nuclei close to a paramagnetic center, and independent of molecular size. Paramagnetic interactions can lead to large dipolar tensors in the solid, containing information unique to the solid state.;In this work, we present the first solid state NMR study of a protein model system with an artificial paramagnetic center. The model ubiquitin was labeled with a double lanthanide binding tag (LBT) to tune the extent of paramagnetism by choice of lanthanide. We investigated paramagnetic effect in the solid for both a weak paramagnetic lanthanide (cerium), and a strongly paramagnetic lanthanide, (terbium) in comparison to a diamagnetic reference (lutetium), and assessed the general applicability of the LBT for solid state NMR. We obtained excellent spectra of the diamagnetic form, clearly indicating the model behavior of the construct. The spectra acquired of the paramagnetic samples based on standard solid state NMR techniques show lower resolution, but for cerium were able to detect residues close to paramagnetic center. This work paves the road for future studies of our model, including the influence of deuteration on solid state NMR line width of a paramagnetic protein.