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"In our experiments, we explore couplings between atoms in proteins," Rienstra said. "Our goal is to translate genomic information into high-resolution structural information, and thereby be able to better understand the function of the proteins." Solid-state NMR spectroscopy relaxes the need for solubility of the sample. In solution NMR spectroscopy, molecules are allowed to tumble randomly in the magnetic field. In solid-state NMR spectroscopy, molecules are immobilized within a small cylinder called a rotor. The rotor is then spun at high speed in the magnetic field. "With increased speed and sensitivity, we can obtain very high resolution spectra," Rienstra said. "And, because we can resolve thousands of signals at a time – one for each atom in the sample – we can determine the structure of the entire protein." To improve sensitivity and accelerate data collection, Rienstra's group is developing smaller rotors that can be spun at rates exceeding 25,000 rotations per second. The faster rotation rate and smaller sample size allows the researchers to obtain more data in less time, and solve structure with just a few milligrams of protein. The determination of protein structure benefits not only from improvements in technology, but also from the researchers' novel approach to refining geometrical parameters. Structure determination is normally based upon distances between atoms. Rienstra discovered a way of measuring both the distance between atoms and their relative orientations with very high precision. "Using this technique, we can more precisely define the fragments of the molecule, and how they are oriented," Rienstra said. "That allows us to define protein features and determine structure at the atomic scale." Rienstra described his group's latest findings and techniques at the national meeting of the American Chemical Society in August 2008. The work was funded by the National Science Foundation and the National Institutes of Health.
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