Dynamic nuclear polarization of nucleic acid with endogenously bound manganese

We report the direct dynamic nuclear polarization (DNP) of C-13 nuclei of a uniformly [C-13,N-15]-labeled, paramagnetic full-length hammerhead ribozyme (HHRz) complex with Mn2+ where the enhanced polarization is fully provided by the endogenously bound metal ion and no exogenous polarizing agent is added. A C-13 enhancement factor of epsilon = 8 was observed by intra-complex DNP at 9.4 T. In contrast, conventional indirect and direct DNP experiments were performed using AMUPol as polarizing agent where we obtained a H-1 enhancement factor of epsilon a parts per thousand 250. Comparison with the diamagnetic (Mg2+) HHRz complex shows that the presence of Mn2+ only marginally influences the (DNP-enhanced) NMR properties of the RNA. Furthermore two-dimensional correlation spectra (N-15-C-13 and C-13-C-13) reveal structural inhomogeneity in the frozen, amorphous state indicating the coexistence of several conformational states. These demonstrations of intra-complex DNP using an endogenous metal ion as well as DNP-enhanced MAS NMR of RNA in general yield important information for the development of new methods in structural biology.