Chemistry professor Chad Rienstra has revealed that a combination of custom-built spectrometers, novel probe designs and faster pulse sequences gave rise to unique capabilities for probing protein chemistry and structure through the use of solid-state nuclear magnetic resonance spectroscopy.
This work attains significance as it represents significant progress toward atomic-scale resolution of protein structure by solid-state NMR spectroscopy.
The researchers say that their technique can be applied to a large range of membrane proteins and fibrils, which, because they are not water-soluble, are often not amenable to more conventional solution NMR spectroscopy or X-ray crystallography.
"In our experiments, we explore couplings between atoms in proteins. Our goal is to translate genomic information into high-resolution structural information, and thereby be able to better understand the function of the proteins," Rienstra said.
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, which is then spun at high speed in the magnetic field.
"With increased speed and sensitivity, we can obtain very high resolution spectra. 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," Rienstra said.
With a view to improving sensitivity and accelerate data collection, the researchers are working on smaller rotors that can be spun at rates exceeding 25,000 rotations per second.
They say that faster rotation rate and smaller sample size will allow them 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 has 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. That allows us to define protein features and determine structure at the atomic scale," said the researcher.
Rienstra will describe the latest findings and techniques at the national meeting of the American Chemical Society, to be held in Philadelphia, August 17-21.