Conventional solid-state nuclear magnetic resonance (SSNMR) methods for the measurement of interatomic distances rely on the measurement of magnetic dipole-dipole couplings between nuclei, which become vanishingly small for distances exceeding 5 Å. The introduction of a paramagnetic center into the system of study generates electron-nuclear couplings which are several orders of magnitude larger than internuclear couplings given that the magnetic moment of an unpaired electron is roughly ~660 times larger than that of a proton. As a consequence, interesting spectral effects are observed, including paramagnetic shifts and enhanced transverse and longitudinal nuclear relaxation rates. Most importantly, long range distance restraints can be extracted from these paramagnetic effects and used in the structural analysis of biological macromolecules.
This thesis is organized as follows. In Chapter 2, 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 radiofrequency pulse schemes and covalently attached paramagnetic tags to enhance protein 1H spin-lattice relaxation.
In Chapter 3, we investigate the effects on such measurements of intermolecular electron-nucleus couplings and intrinsic metal binding sites, both of which may potentially complicate the interpretation of Paramagnetic Relaxation Enhancement (PRE) data in terms of the intramolecular protein fold. In Chapter 4, we present an approach that enables rapid determination of the global protein fold via measurements of nuclear paramagnetic relaxation enhancements (PREs) without the use of conventional internuclear distance restraints.
Finally, in Chapter 5, we present solid-state NMR studies of the K28C mutant of protein GB1 intentionally modified with 2-[1,4,7,10-tetraazacyclododecan-1-yl]-ethanethiol (TETAC) side chains with a high affinity for transition metal ions like Cu2+, ZnZn2+, Co2+ etc.