Rapid Acquisition of Multidimensional Solid-State NMR Spectra of Proteins Facilitated by Covalently Bound Paramagnetic Tags

We describe a condensed data collection approach that facilitates rapid acquisition of multidimensional magic-angle spinning solid-state nuclear magnetic resonance (SSNMR) spectra of proteins by combining rapid sample spinning, optimized low-power radio frequency pulse schemes and covalently attached paramagnetic tags to enhance protein H-1 spin-lattice relaxation. Using EDTA-Cu2+-modified K28C and N8C mutants of the B1 immunoglobulin binding domain of protein G as models, we demonstrate that high resolution and sensitivity 2D and 3D SSNMR chemical shift correlation spectra can be recorded in as little as several minutes and several hours, respectively, for samples containing similar to 0.1-0.2 mu mol of C-13,N-15- or H-2,C-13,N-15-labeled protein. This mode of data acquisition is naturally suited toward the structural SSNMR studies of paramagnetic proteins, for which the typical H-1 longitudinal relaxation time constants are inherently a factor of at least similar to 3-4 lower relative to their diamagnetic counterparts. To illustrate this, we demonstrate the rapid site-specific determination of backbone amide N-15 longitudinal paramagnetic relaxation enhancements using a pseudo-3D SSNMR experiment based on N-15-C-13 correlation spectroscopy, and we show that such measurements yield valuable long-range N-15-Cu2+ distance restraints which report on the three-dimensional protein fold.