Development of new 17O NMR spectroscopic techniques for studying biological systems

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Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical technique for studying molecular structure, dynamics, and chemical bonding. The development of this technique over the past several decades has revolutionized chemical and biological sciences. However, most successful NMR studies of biological systems such as proteins and nucleic acids are primarily based on detection of atomic nuclei with a nuclear spin quantum number of 1/2 such as 1H, 13C, and 15N. On the other hand, the oxygen element, being one of the most abundant in organic and biological molecules, has not yet been accessible by NMR spectroscopy. This is principally because the only NMR-active oxygen isotope, 17O, has a nuclear spin quantum number of 5/2 (known as a quadrupolar nucleus). In addition, the natural abundance of 17O is extremely low, 0.037%. Quadrupolar nuclei are notoriously difficult to study by NMR because they often give rise to very broad NMR signals. As a result, 17O is very often considered to be "NMR invisible" in the context of biological macromolecules. Recently, we made two breakthroughs on the way of solving this challenging problem. First, we have developed new NMR methods that allow detection of high-resolution 17O NMR spectra for biological macromolecules both in the solid state and in aqueous solution. Second, we have demonstrated a general method of incorporating 17O into recombinant proteins with auxotrophic E. coli strains. In the next 5 years, we will apply these new methods to two types of biological systems: proteins and live cancer cells. 17O NMR spectroscopy of proteins is often considered to be the last frontier of biomolecular NMR. We will explore the unique information that 17O NMR can offer in the study of protein structure and dynamics. We will investigate the use of 17O NMR as a new tracer for monitoring glucose and glutamine metabolism in live cancer cells. This will help establish 17O NMR as a complementary tool potentially useful for cancer diagnosis and monitoring. The ultimate goal of our research program is to make all major elements (H, C, N, and O) found in biological molecules equally accessible by NMR spectroscopy. In this field, our research program has been an international leader. The outcomes from the proposed research will have impact in many disciplines in chemical and biological sciences. The proposed research program will also provide excellent opportunities for training of the next generation of highly qualified personnel to be competitive globally.