New Direction in Nuclear Magnetic Resonance of Copper and Zinc Ions in Biological Systems

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Metals and their ions are indispensable for life, and as such more than one third of all proteins in biological systems require the presence of metal ions to function. Several transition elements, including copper (Cu) and zinc (Zn), have been proven to be essential for humans, and occur in the body at trace amounts (mg to g). Cu and Zn are both necessary for life, but toxic in excess, and therefore their homeostasis has to be tightly controlled. In order to understand the role of Cu and Zn in the body, it is of profound importance to understand the binding chemistry and the coordination environment that these two metal ions adopt in their biological context. Unfortunately, the absence of convenient physical and spectroscopic properties to study the local structure and dynamics at the metal sites has so far held back a detailed understanding of Cu(I) and Zn(II) biochemistry. ***Nuclear magnetic resonance (NMR) spectroscopy is probably the most powerful single technique to explore the structure and dynamics of molecules in solution, and therefore, it contributes fundamentally to the advancement of biological sciences. In practice, however, NMR suffers from poor sensitivity for several elements across the periodic table, including both Cu(I) and Zn(II), mainly because of the low gyromagnetic ratio of their NMR-active stable isotopes and intrinsically small signal-to-noise ratio. Furthermore, both nuclei are quadrupolar (spin > 1/2), leading to resonance lines widths in the kHz range or beyond detectability, which makes it inadequate for many frontier scientific applications. As a result, only a very few solution-phase NMR studies on Cu(I) and Zn(II)-containing biological systems can be found in the literature. ***This proposal seeks funds to investigate the coordination chemistry of Cu(I) and Zn(II) metal-binding sites directly in several metal ion complexes and metalloproteins using the newly established liquid-phase beta-detected NMR (beta-NMR) spectroscopy. Beta-NMR employs radioisotopes rather than stable isotopes, and it allows for measuring NMR signals by detecting the beta particles emitted by polarized, radioactive ions. It offers 1010 enhancement in sensitivity as compared to conventional NMR spectroscopy, and it can be applied to many elements across the periodic table, including both Cu(I) and Zn(II). For the past 2-3 years, TRIUMF has been working on the design and implementation of the liquid-phase beta-NMR spectrometer at the ISAC-I facility at TRIUMF, Canada. Testing is now completed using Mg-31, unambiguously establishing that beta-NMR is capable of measuring high-quality NMR resonances with resolution better than conventional Mg-25 NMR, using as few as 107 Mg ions in 2-3 L of liquid solution, and within less than an hour. Given the recent accomplishments, we are now well poised to conduct pioneering beta-NMR measurements on different Cu(I) and Zn(II) binding biological systems.